IG Chemsitry Papers

.I.G.C®S.E

h

i

Prof. Dr. Fathy Abdel Galil

-

:

·.

Chemistry IGCSE

(Dr.rathyADC\el uatuJ

Contents Ef'~

Topic L

Topic 2.

. To.pic 3.

Topic 4.

Topic 5.

Topic 6

The particulate nature of matter .........•.....................................•. States of matter·.......... : ............................................................. . . partie . 1e theory ................................................................ . K.metJc Diffusion ............................................... , ............................... . Experimental technique ..•......................................................... Laboratory apparatus ................................................................. . Safety in laboratory .................................................................. .. Methods of purification ............................................................. .. Separation of mixtures ............................................................... ·. Chromatography ~ .................................................................... .. Atoms, elements and compounds .............................................•.. Atomic structure ..................................................................... . .Radioactive isotopes ................................................................ .. . Electron distribution ............................................. :.. ................. . lons and ionic bonds ................................................................. . Molecules and covalent bonds ..................................................... . Macromolecular (giant) structure .................................................. . Stiochiometry ........................................................... .'.......... .. Chemical formula .................................................................. ·.. . Chemical equations· .................................................................. . Chemical calculations .............................................................. .. The mole .............................................................................. .. Empirical formula and molecular formula ........................................ .

1

1

2 6 8 8

10 12 12 14

16 17 19 20 22

25 28 30

30 33

35 37 ·44

46

The periodic table ................................................................. .. Trends in group I [The alkali metals] ............................................. . Transitions elements ................................................................. . Trends in group VII [The halogens] ................. ·.............................. . Nobel gases .......................................................................... .. Test and collection of gases ......................................................... . Oxidation and reduction ............................................................. .

48 51 52 55 56 58

Electricity and chemistry [Electrochemistry] ................................. . Electrolysis ............................................................................ . Applications of electrolysis ........................................................ ..

6D 62 67

Chemistry IGCSE

Topic 7.

Topic 8.

Topic9.

(Dr.FathyAbdel Galil)

Acids, bases and salts .-............................................................. . Acids ............................................................ , ...................... . Bases ................................................................................... . The pH scale .......................................................................... . 1vfaking salts ........................................................................... . Types of oxides ...................................................................... :. Identification of ions ................................................................. .

69

69 71 72 73 77 79

Metals and reactivity series ..................................................... ... Alloys .............. c •. : •.. ; •..••...•••..•.•..•••.•..•.•••.•••••••••..•..•..••.••••.••.•. R.eacfIVI"ty senes . ....................................................................... . Extraction of iron ................................................... ·.................. . Steel making .......................................................................... . Extraction of zinc ..................................................................... . Rusting ................................................................................. .

90 91

Chemical changes Production of energy ................................................................ . Electricity from chemical reactions .............................................. .

95 97

Topic 10. Chemical reactions ····································'····························· Speed of reactions ...................................................... . :........... . Reversible reactions ................................................................. . Chemical equilibrium ............................................................... .

81 81 83 88

89

99 99 106 106

Topic 11. Air and water •••........••..•..••.••.•.•..••..•••••..••••.•.•••..•••.•••••..•••..•••• Purification of water supply ...................................................... .. .. f. ·. ComposttiOn o atr ................................................................. .. Manufacture of ammonia .......................................................... . Fertilisers ................................................ : ............................ . Air pollution .......................................................................... .

108 108 109

Topic 12. Sulphur ............................................................................. . Making sulphuric acid ............................................................. .

116

Topic 13. Carbonates ........................................................ ,..................

118

Topic 14. Organic chemistry ................................ ••.•...•.•••••• .•••..••••. .• ..... ..

120

111 ll2 113

117

- -··

Topic 1:

[Dr. Fathy Abdel Galil]

- 1-

Chemistry IGCSE

. THEPARTICULATENATUREOFMATIER

All matter is made .up of tiny particles, These may be atoms, mole_cules or ions. Using the idea of parti?les, we can explain the way matter behaves.

States of-Matter All matter can exist in three ·states- solid, liquid or gas. Solids have a fixed shape. Liquids have no fixed shape, but their volume is fixed. Gases have no fixed shape or volume. They spread out (diffuse) to fill all the available space. Unlike solids ang liq~ids, gases are easy to compress into · smaller size. The state of a substance can be changed by heating or cooling. 6Jt.eez.i.ttg

c.onde.Jt6.Wg

me..Wng

so LID

f W.r

)-

f"i

y

w

bo-U-Wg

0 0

.JDI

0 0

0

LIQUID

u

0.. GAS

iodina cry
. on cool test~tube

Sublimation This is the change of state from solid to vapour and back from vapour to solid without passing through the liquid state. Iodine, for instance, behaves like this

purple Iodine vapour.

lodine cry•tal• ---.JS''fK.I

gentle

heat

heat

solid iodine [dark grey solid]

allow to cool iodine gas ------+solid iodine [purple vapour]

Solid carbon dioxide behaves similarly.

(Dr. Fathy Abdel Galil)

-2-

Chemistry IGCSE

:.':

Arrangement and Movement Particles

SOLIDS -

LIQUIDS

GASES

·')( )()J )(

T)ll 'l. X

!()"(

;-.... ..:=: >--(-' :>--< --'.r"[

( )[ " J: "'[_ J:

J[

0 0 0

0

0

0

0·

..

.'

Arrangement of Particles

close together in a regular arrangement

still close tog ether in an irregular arrangement

particles far apart

Movement of Particles

only vibrate in their places

can move around slowly

free moving rapidly

Kinetic Particle Theory 1. All matter is made up of very small invisible particles (atoms, ions or molecules). 2. The particles move all the time. The higher the temperature, the faster they move. 3. Lighter particles move faster than heavier ones .

.J

4. In a gas, there is relatively large distance between the particles. They are free to move anywhere [i.e. a gas can fill any v.olume].

Using the idea of particles and kinetic theory, we can explain the changes of states of matter and diffusion .

...

;·..

- 3 -

(Dr. Fa thy Abdel Cali!)

Chemistry IGCSE

Changes of State

Mel.:thtg When a sol~d ~s heated, ~ts part~cles ge~more ene,gy and v~brate more. Th~s makes the sol~d

expand.

At the melt~g po~nt

the part~cles v~brate so much that they oreak-aYay from the~r pos~t~ons. The sol~d becomes a liquid.

nrraan·a· o·' " ........ ".,

'offifi8§.

heat

heat at

O:ffil..DOG DQO: · "0'0' .

:a.: 'G ' .........

melting point

·-

........

~

!he partici!"S vibcate.~~T~

a liquid is formed

Mel.:thtg Po.zn.t ~s ~nto

a

the temperature at

wh~ch

the

sol~d

melts,

~.e.

changes

l~quid.

Bo.<.Ung When a

liqu~d

move faster.the

part~cles

Th~s

is heated, its particles get more energy and makes the

liqu~d

expand. At the boiling

get enough energy to overcome the forces

them together. They break away from the

liqu~d

po~nt,

hold~ng

and form a

heat

boilino point

slow-moving particles in liquid

the particles move faster

the particles get enough energy to escape

Bo.<.Ung Po.ln.t is the temperature at which

the

l~uids

bo~l,

i.e.· changes

into a gas.

Pure substances have fixed and definite melting points and boiling points, e.g. pure water boils at 100°C and freezes at 0°C.

- 4 -

Chemistry l GCSE

(Dr. Fathy Abdel Cali!)

Evaporation When left open to the atmosphere, even b~W

when a

~quid ~

Well

the boLt£ng poLnt, some particles of a liquid escape into

the gas state. -This is called evaporation. The rate of evaporation increases vith o c

increasing temperature increasing surface area.

A poht.t to Jr.emembVt ~ .tlw.t evapo~on oc.c.u.Jti. <.pon.:ta_neou&./'.q a_t anq i:.empeJr.a..:tuAe-, bu;t boiling oc.cJLM lli:. c.elr.i:.a-Ut tempeJr.a..:tuAe wfti__cJt .U. the boiling poht.t.

Compressing a Gas

plunoer pushed in

0 oas particles

0

0

0 0

0

lL_

0 0

0

o o

ThVte ~ a !_at a 6 .6 pa_c.e between the p/Vr..t{_cl.u bt a_ gil<.. You c.a_n 6oJr.c.e .the pa_ll..U_c..tu elM Vt •••

0 0 0 0

of-, gas compressed

0 0 0 0 0

0

0

0

inlo a smaller

I'Oiume

bq ptUhlng bt the p./'.ung Vt. The gM g ei:..6 <.queezed oJr. c.omplr.e<..6ed .into a_ <.maUVt vo./'.ume.

·If enough force is applied to the plunger, the particles get so close together that the gas turns into a liquid. But liquids and solids can not be compressed. because their particles ara already close together.

:.

....

- 5 -

Chemistry I GCSE

(Dr. Fa thy Abdel Gali!)

Temperature changes when a solid is heated I I I I

I

I

t 'Temperature boiling _ point

}i____________ }!

~ boiling

melting point

T I. "3• -- -

'------y----' melting

I I

'

Time~

Qu.e.ction Look at the table.

substance

state at room . temperature

carbon dioxide

gas

iron

solid

w.ater

liquid

From the table, choose: (i}

one substance which can be easily ccmpressed at room.temperature,

\

\\•

q('

•.•••1:"€\:. ~;?. :.: .Y.,;.?.6.lE.. :......................... ~---··············· .............................................. [1 J (ii)

one substance which consists of particles which are far apart at room temperature,

(iii)' one substance which has a fixed shape at room temperature .

... i!'(tJ .....................................................................................................................[1]

Chemistry IGCSE

- 6 -


Diffusion This is J,piteac:Ung oat and m.Lxhtg pMeeM, seen mainly in gases and liquids. The particles of one substance mix with and move through the particles of another. Diffusion goes until the mixture is· uniform.

In otheJt. WoJtciJ,, i.;t i.A .the movemen.t an pcvd-{.de;, nJLOm JtegioM o6 /U.gheJt. c.oncen:tJtatiort .(.n.to Jteg.<.oM On loWelL c.onc.e.n.t;luztion. Diffusion is fastest in gases. The particles in gases are moving faster than in liquids. The rate of diffusion· depends on the molecular mass. The smaller the molecular mass the faster the rate of diffusion.

I. The bromine diffusion experiment: Bromine is a red-brown liquid which vaporises easily at room· bromine temperature. Some of the liquid is liquid '\ placed at the bottom of a sealed gas ~ jar. The red-brown bromine vapour spreads out to fill the gas jar.

bromine vapour

. 2. Diffusion of ammonia and hydrogen chloride

a) Co.t.ton wool .60a.ked .<.n ammon.<.a.· 4olu.t!-on a .tong .tube. I.t g.{.ve;, o66 ammon.<.a. ga.;,.

.U, pu.t

.<.n.to one end o6

b) A.t exactly .the
aud .u, pu.t .{.n.to .the o.theJL end hydlt.ogen c.hlo!Ude ga.;,.

06

the .tube. I.t g.{.ve;,

c.) The g. · e6 d.{.6tju.;, e a..tong .the .tube. Whi.;te

0 66

solid o6 ammonium

chlo!Ude 6ai!Jn,l wheJLe they meet.

calion wool soaked In ·

glass tubing

eolian wool soaked In

ammonia

hydrochloric

solution

acid

+

Mr

white solid forms here

17

HCI(g)

->

NH CI (s) 4

36.5

Ammonia deffuses faster than hydrogen chloride. Why? . :~'.' ;': '..... ' ...

- 7 -

3UOI V1HJ3.T .JA T~~3Mi9.39X3

li

I!

3. Iffew dro~s of potassium manganat!:_.(Y.:q) solutio),! .(p,urple) are carefully ~ded to a beaker cdfit!Jifu'W~Ate~;ftli>~&pl.!fei:oloration will be eq#tlly distribute~ throughout the solution. ~~

U ~.

:;

H

i;,. . ~

H

lI

t\O/

1

It is difficult?p explain t4~ above aiasetvations with,ouf using the t'"'tes. r ;' z·dea o1,.{'par~ · i.. ,t >:"' ,1 \, ~he observa#:ns _give a~ r/;Nidence~or {he movem(:nt oj:farticles 1 m gases andHzquzds. !! k, !, / ,\ I t : r , 1 -ll !

·1-.

- 1-t u;

~

t

1 ! '··-~--.·-'

l'-------~--)

"-----'·

,f

::.:<·~t:.A

f 1 ••

The dia~ilaiiV':T'hows the diffusion of the exhau~ ..t gases from a car~ol!~•;/ ~

·

;\!Lt'JJ..~-!:l..B~!:>

.

when they meet the ~I;:~J:q

.L~D.tOO:)

)/a!LL1

·.,a.SaJiv,::

;.:.'.;· (l'lJJd

i . - -•. r~.-----./

.

t..~~.j\>J Q...~!;l';i .".1-~!--!!~~J.i.~>-':..Th

i·\) ~

,,:,:, up:0rr\8is'2or#s'ih 'air

/~. '

0

q:n:;!~:r

··.,,...~~,

.,,,

.....

··-~,;..,

··;·~~

(j

,.. -%:l[e __ some other_ examples of diffusion.

\=· / '' ;/.

"~t- ~~~"f""'t

.. , .OJfo~o ·.· G]/.(1,:, 1{:-, ct~s i:of f!"" r:>i
,_, •Jo

4

".'•

•

•

•

•

•

""oro o

''

bOtJhl

ll

/;'!I.f

'

. ;/

-

• • • • • • • . . • • //. ....•..•.•..

'.'/

,'If

'I

....Ji!•

0

'<--....._

;;;li 9

o o • •

"" o •

•

•

•

•

•

.,,_~ •

•.• •

1_,·-~- -~--.

;..•;:.:...:·••

0

•

•

•

o o •

'-,. ' ..

h), ;~.e;!,a~!ll "'-":"''·1 ;l •l . ""'lUI!!O?. . ......~ ~ iQ! 1\ 1'~ri:f;:<.i . '.!.--~.-:---.. ...,........................... .

-----·

-~

_)

= ··--"

1-<"

··-.:-----~

i!t

l

•·

o

-..l

\1

-----·

.

1liiW blc•pil--V!ii!neb. ·uhvc!

riJiw biup-:1 '-!iizn!}b ;srlairi .c-~r--

/-

4.

~

( \---Ll \ 1,___,__ _ _ _ _ _•.

o o •

Topic 2.


- 8 -

Chemistry fGCSE

EXPERIMENTAL TECHNIQUE

Laboratory apparatus

·:.·

u

tap

beaker

conicnl flask

measuring cylinder

pipet to ~rette

6oiL a.cClll
mo~Lta.~L

~ watch glass evaporating

baa in

~'"'""

funnei

6 6

crucibla and lid

.bunae.n

burner

thermometer --li
Iowa: density liquid with

. hlohor density

{Oi!QS

balance

Chemist•·y IGCSE

(Dr. Fathy Abdel Galill

Dissolving solids in water ~a. goo<(SO"lve!}Dror many solids. Im3.gine stirring spatulas full of copper sulphate crystals into water. At first it is easy to dissolve the solid in the water to make a solution. Eventually, as more crystals are stirred in to the solution, no more will dissolve, The solution·is saturated. A saturated solution is one in which no more solute can dissolve at that temperature. Making a solution saturated copper sulphate ro!ution

water Is a

more copper.

•ulphate cry :;tal, ~

copper

sulphate Is a solute

solvent

+

A solvent is the

solute

saturated solution

solution

liquid that docs

A solute IS the substance that

the dissolving.

is dissolved.

A saturated

A $Oiution is fonned when a rolute is dissolved by a solvent.

:rolution "is one that will dissolvt no more wlutc at that temperature.

Chemists often need to know exactly how much solu.te is dissolved in a saturated solution. This is called the solubility. The solubility of a solid in water is the number of grams of that solid that. will dissolve in 100 g of water. If the saturated copper sulphate solution were heated, much inore solid could be dissolved in it. Most cqmpounds dissolve inore in hot water than in cold. Their solubility increases wjth increasing temperature. A graph can be plotted to show how the solubility of a compound changes .. with increasing temperature. This is called a: solub!Iity curve. Solubility curves for various compounds

D1

~/- 1 -Jute

'.

,(

25 0

/

/

.g' 200

/

2m

;: 0>

8

/ .............

150

c

"

!)

ll

· ·trate ~\UI1'\~

100

r,;..

0

50

'-

)f:-'' '

0

4

-

..--e / / •<..(0'\J

v

f. \\\ ?'<$9\1}~.,.......,!'V~'

l:l m

::;:

---:;

y

~

-

...:

... 20

40

60

Temperature/"C

80

100

.

~~-p""!v:"

,h?::-4

I' /1

D~~<"t:>I~~.L

L.-

c.cf_

,'--'. ,._,), : ,,.,,-\

L)

-

Chemistry IGCSE

- 10 -


Dissolving is an example of a phy¢.i.c.rtl c.!:ange.. Other physical chan:;;es include boiling, melting, evaporation. If the ·solvent is water, the·solution is called aqueous solution (aq). A concentrated solution is one which contains a high proportion of solute. A dilute solution is one which contains only a small proportion of solute.

How would you make a sample of sea water more concentrated 7

. .16: d... ;·?!: ~· ... r.'?f: ... ~. ';'~\ ....................................... .. •

•

•

~

•

v

••••••••••••

0

••

0

•••••••••••••••••••••••••••

0

••

0

••••

0

.............

0

••

·safety in the Laboratory Some chemicals are

~articularly

hazardous. These are pointed out

by standard tiazard labels.

{a)

:tauc.

chlorine, bromine, carbon monoxide

{b)

C.OIVW¢.f.V e

concentrated solutions of acids ~nd alkalis such as concentrated sulphuric acid

{c)

oucU.o.i.ng agent

potassium dichromate~ potassium manganate.:

{d)

.£.i'.ammable

ethanol, petrol , .. hydrogen

Chemistry I GCSE

(Dr. Fa thy Abdel Galil)

- 11 -

Laboratory Rules for Working in a Laboratory

DON'T

DO

e run in the laboratory o eat or drink in the lzbt:re.::ory ill> piay with fire, electrical switches or chemicals look down a test tube that is being heated, or point it at anyone

e keep bags and coat safely out of the way e tie up long hair and tuck in ties and loose clothing e wear goggles or safety glasses when doing experiments o keep your place tidy and wipe up spills of chemicals o ask if you are unsure about anything

....

·, §~~~-~~i~El_EE~~~~E~~~~-~ 1- Carrying out the experiments which involve toxic gases and strong smelling gases in fume cupboard or' in we'fl-ve'rlfilated laboratory.

a

2-

Wear gloves when doing experiments with corrosive substances

3-

For heating a flammable liquid use a hot water bath.

This diagram shows a student working in a laboratory.

Identify two safety problems In this scene. I ....,V\_

,?~

1•

u·

~

!

I

!· - ,

~-,.

\.

I

S arety pro bl em 1 .................... ,............................................................................ ,;;·· .. •·•·................................. . .·'I!... I"~

l_

\_

··~

·urr>.

·'C'.'k\0

.................................................................................................................................................................... [1 1 '

Safety problem z .....

.'

0

I

-"

l

\

?.:::.::.......... ..l.R:?.!L"f..:..........::o:.......:................~..~'............ :::-~.:::::..............................

..................................................................................................................................................................... [ 1]

- lZ -

Chemistry IGCSE

(Dr. Fathy Abdel Galli)

Methods of Purification

17'--filter paper · fimnel residue.

a) To .5epaJta..te a. 6Mm a. Uqr.Ud

Mild (J.n.6 o.tub.te)

Filtration The solid is left on the filter paper as the residue while the liquid passes through.

Just by pouring the liquid insoluble

off from the solid,

b)

To

ob~

substance

a. .5o.Ud 6Aom a. .5o.f.utLon

t:===::J-..J-salt solution

A solution consists of a solut.e dissolved in a solvent, Sea water is a solution

solution~-_____ evop oratlng :- .. -~_.... ba.s: 1n

/ gauze·

---

of salt (sodium chloride) in

K~~r

water. By heating the solution, water evaporates and solid ·salt ·is left,

! -----

c ..... -

'%?~~~-

:C,c;eifc!c"(

I

I ~

I

__.- ~'~ I

·

tripou·

.f1__/ / ,

u

The solution is evaporated to the crystallization point; i.e, the point at which crystals of solute will form on cooling the solution to room temperature and can then be f"iltered out, and dried.

What method could be used to show the crystallising point had been reached •

'I'

'""' -'r ,) ~,- t I_ ' -::,•.::-,,_i \ - ) v •· · ••••••••'-r•:f·••••••••••·•••••••••••••••••••••••••••••••••••••••••••••••• v

•••••••••••••••••••••••••••••••••••••••••••••••••••••••• '

........... t

••••

- 13 -

Chemistry IGCSE

c)

To

a 6olvent

4epaAaXe

6~om

(Dr. Fathy Abdel Gal!!)

a 4otution

Distillation ------------

_

tharmometor

When the solution ia boiled, the solvent changes to vapour, the vapour passes down· a condenser where it is converted back to liquid and is collected as the distillate.

sea water

d}

To

6 epaAaXe

cold W;ttcr in pun distilled

HEAt

:iJJJo .Uqu).cL6

water

Fractional distillation ----------------------Miscible liquids (i.e. ones that mix together completely) may be separated by fractional

distil~

thermometer

lation provided that their boiling points are different, e.g.

Cr;Jolest paQ:·

of column·---

mixture of ethanol and water, The mixture in the flask is heated so that it boils. Both

cold water In fractionating ---W~

column filled with tilc:ss rods

go up the fractionating column. Ethanol has a lower boiling point

Frt~ctlons

collected at

(78°C) than water (i.e, is more

lower temperatures.

volatile), The liquid with the lOI
z

~8

ethanol vapour and water vapour

reaches the top of the column

1

broka_n Porcelain

HEAT

first.

Ant£-bump.i.ng gMnui.e6 [alL bMk.en polLc.eta.i.n} alLe. added .to .the. m!.xJwc.e. .to acfU..eve 6.teady bo-UJ..ng. Important appli<;:a·tions of fractional distillation : a)

The separation of liquid air into oxygen and nitrogen

b)

The separation of crude oil [petroleum] into useful fractions.

3

- 14 -

{Dr. Fathy .Abdel Galil)

Chemistry lGCSE

e.)

Clvr.omCLtogJutphq

Paper chromatozraphy is used to separate a

'

mixture of similar solids dissolved in a

0 :

solvent, e.g. it can be used to_separate

the dyes in ink. It can also be used to identify additives in foods such as flavouring and. colouring;;.

A

- Filter paper

0

r

0

small .spot

of the solution containing the mixture

The. 6po.t nuu.t be. ab.ove .the .tevel o 6 .the bofvent

-

is placed near the end of the filter

Solvcnl

paper. The end of the paper is dipped into a solvent (e.g. water, ethanol). As the solvent rises up, spots of various consti.tuents of the mixture will be collected at di{ferent distances above the original spot. The finished paper is called clvr.om~og~. A single p~e. substance will produce.only

one. .opa.t. Chromatography can also be used to separate calaunle46 substances, but .in this case the paper must be sprayed with another chemical

[tac.atilig ILge.nt) so that the position. of the s.pots. can be seen.

Example. a 6 LL!.l.Wg clvr.ama;togJutphy

3

A dye used in food colouring

f--- ---"----.--- ~- --------f

can be ide:ntified by chromategraphing it alongside some pure, known dyes. In this way,-a public

movement

of solvent

1---------------f

analyst can firid out whether a dy_e used iri .food is a permitted one

f

or an 'illegal' one. The figure shows that dye: 'A' is a mixture, and it contains dyes

1

C1 and

1

A

D'·.

8

c

0

ED

samples -of dye A. and pure chemicals B, C, 0, E. added along !his line as shown

I 6 a. ,o po.t Jt.e.ma...i.M on. .the. ,o.ta.Jt.,ti.ng -Une., .U me.ILM ~ .the .o ub.o.ta.nce.

;_;, .{.n.Miubie. .W .the. <> otve.n.t

Why mU!.l.t .the. .o;taJLt.{.n.g

U!.l e.d .

., •e. be. dlurWn. V<-"

.w

pe.n.cM:. iLn.d nat w.Uh ink ?

····~--~·-·······················································-····

........................................ ~ ................................... .

-

15 -


Chemistry IGCSE

The diagram shows a chromatogram used to find out which colourings are in a fruit drink.

.

f

I

'

I

9

'

1

fruit drink

f 2 3 4 colourings

5

Which two colourings are in the fruit drink?

A

1 and4

8

1 andS

2 and3

C

@

2and5

Testing the purity of a substance A

puJLe substance has nothing else mixed with it. A substance is not

pure when it has other things mixed with it; these are called irup~e6. Chemists often need to know if a substance is pure. For example, drugs must be tested for purity before they are sold. Impurities might harm the patient.

7. Chlr.omatog1taphy c.an be Ul>ed :to .6ee

8'--~>

\:;u_\::\::::"<>"

J.o \'__

~'y.,

az

~o\__

eo'"

-to

a. .6!Lb.>.ta.nc.e -L.6 puJte. How

\\c-.~

0"-·fl"'--'

• • • 'l. . . . . . ~ •• ~--u··························::.··t···I

<2Y'-

\\.:::

·, ",

~ v.'\"

?

',\. , < \_ o·~\;;, <:>'0. ............. \.j'""""'""

,

2. Ano.:the1t wa.y o 6 :te<>:ti.ng puJLUy i;, :to meMuJte :the .>ub.6:ta.nc.e' .6 me-tUng po-i.n:t otr_ ba.i..Ung po.i.11-t. PuJLe .6ub.6:ta.n,c.e<> have de6-Lnile me.Uhtg po~ a.nd bo.LU.ng po~. I o a. .>ub.6.ta.nc.e -i..6 no:t puJte, m me..U.Utg po.ill:t otr_ bo.LUng po-Ln:t w.U.t be d.i.o oe1len:t 6Jtam :the known. Impurities make melting points lower and boiling points higher.

The WCLte1t .ta.R.en 6Jtom ;the .6ea. 6Meze<> at a.bou:t -2'C a.nd boili at 70 1"C. I.6 U pWLe ? No 1

..................................................................

Why ?

Gu:."-'-'S':

-,~

s"""'"\.1\ : ~f'~::·ze

:C,L

c- ) ".

··································~··········--··~

.......... .

- 16 ..

Chemist1·y I GCSE

Topic 3.

(D1·. Fathy Abdel Cali!)

ATOMS, ELEMENTS AND COMPOUNDS

Elements, Compounds and Mixtures Element : is a substance which cannot be split up, e.g. aluminium or sulphur. It contains atoms of only one type. There are over 100 elements which are grouped into two main classes metals and n'on-me tals. Most of elemen t·s are metals. There are only 22 non-metals.

There are a few elements which are d.ifficult to classify Because they have some metallic and some non-metallic pro-

perties.

A comparison of the properties of metals and non-metals Property

Metal

Non-metal

state at room temperature

solid except mercury (liqu1.d)

solids, gases and one liquid (bromine)

melting point

high except alkali metals

low except carbon and silicon

appearance

shiny

dull .

Compound

effect of hamme ring

easily shaped

electrical and heat conductivity

good

brittle - break into pieces poor or none, except

graphite

is a substance made up· of two or more elements chemically combined together. A compound has properties different from those of its elements, e.g. water or carbon dioxide.

Mixture

consists of two or more elements or compounds which have not

been chemically combined, e.g. air or sea water. A mixture has the properties of the substances in it and can be separated by the methods described in Topic 2.

- 17 -

Chemistry IGCSE


Atomic Structure Atoms consist of a minute nucleus, where all·the positive charge and most of the mass of the atom is concentrated, surrounded by electrons. The nucleus is made up of two types of particles

p.li.o.tono and neubr.ono.

A pJto.ton is a positively charged particle. A.neut.li.on is a neutral.particle (uncharged), with mass equal to that of a proton. An elec.t.li.on is a negatively charged particle; the mass of the electron

is so small that it can often be ignored,

Atoms are electrically neutral because: number of +ve protons = number of -Ne electrons.

Ato~e (p.~to.ton) nu.mbeJt :

auiL-a:LomLc.

Rela.ti.v e. Ma.M

Pa.Jt.tic.te.

Cha.Jr.g e. +1

1 1

PILO.tort Neu.bwn

0

-1

1/1810

Etec.tJton

(Z)

is the number of protons in the nucleus.

Ma..6c, (IU.Lcteon)

nu.mbe.~t : (A)

is the total number of protons and neutrons in ari atom. Mas~

No. (p + n)

Atomic No. (p)

X

(symbol of

the element)

Ato~e nu.mbe.~t =

nu.mbeJt

on

pM.tono

MM
.=

nu.mbeJt

p!W.tono

+

nu.mbe.li.

o6 o6

neu..t.li.ono

No. of neutrons = Mass no. - Atomic no.

Question ;

Work out the numbers of sub-atomic particles [protons, neutrons and electron J of the atoms of the following element.i. · · 12c

6 ,

p

c

56 26Fe,

......................................... .

e =

.......... • .......................... .

n =

" ........... • •• • •• • ..... • ..... • • •••••••

- 18 -

Chemistry !GCSE


Isotopes

I<> o:to p eo aJt.e a.tom<> o6 the <1 am.e. el-ement, ULU:h the <. ame numb eM

pM:to IU bu.X. cU£ {, Vtent numb eM 0 6, neu:tJr.o IU , _ .in o.thvr. wo.tc.do i..oo:topu h.aue .the <.ame a.tom.Z.c. nwnbvr. bu.X. cU66vr.ent 0 {,

nutM

numb Vt6 •

I<>o:topeo o6 hydJwgen Hydrogen has 3 isotopes

() Most hydrogen atoms are like this, l H. It is an orcl.inarj hydrogen atom with no neutron.

0

But a few' are like this. It has one neutron. It is called deuterium, 1 H. [2D] 1

,.

0

And some are like this, with two neutrons. It is-called tritium, ~H. [fT]

Isotopes of an element have the same chemical properties.

IM:topu o6 c.a.Jtbon Carbon has 3 isotopes

f.!a..66 nwnbvr.

=

Nwnbvr. o6 plto.toJU

=

Nwnbvr. o6 dec.bta JU = Nwnbvr. o6 neu:tJr.o JU [AJ

is called

=

[A]

( B]

....... ... ..... ... ... ... . ... . . .. . . . . . . . . . . ..... .. . .... . .

.............. ................ ..... . .. ..... .. . .... . . . ... ...

"

[C]

.............. . . ........... . ..

"

..................

...............

carbon~l2.

What do you think

[BJ· and

[CJ

are called ?

.......... ................................................................................ . .,

.. . . .·...................................................... " ............................. . ,:. ..·

- 19 -

Chemistry !GCSE

(Dr. Fa thy Abde! Galli)

Relative atomic masses

Host elements contain a mixture of isot<>pes •. This explains why their relative atomic masses are·noz whole numbers.

The relativ.e.atomic mass. of the etement[f.u] is theaverage:ma&oEits,iS@toges takiug· into ace0unt their proporticms. · For example, chlorine consists.-of i:wo isotol'es with mass ·numbers of 35 and 37. Their proportions a~e--75% of: ~fCJ: an.
The relative atomic mass of chlorine· will be: 35-~- 75/1@0

Radioactive Isotopes

.·

+

37 X 25/100'= '--· •

· . ·· ..

·. ·Sem.e is0tepes (such a5.tri~um ami car!D0n-14].haye tmstable nuclei; they emit certain types of radiatl&n ·[alJ!lha a, "fueta ~, anti! gamma r] in @faer · to Ille mere .staDle.

Some us.es ~of r:[email protected] ;iso.t€!;p,e_s : Me.cU..c.aL

1M e.A : --------------. 1-

e.. g.

Cance-r treatment :

Tumors can be. destroyed- using controlled

doses of gamma radiation from cobalt-60.

2-

Sterilising medical equipments

I!1~~~-~~ ' e..g. 1- Detecting leaks in water pipes.

2- · Checking the thickness of paper during manufacture.

Nuc Iear Power

.. ) ( 235u as a source of_ ener!iJ)'·

Nuclear fission

Some radioactive isotepes are used as nuclear fuels e.g. Uranium-235. When they are bombarded by neutrons, they s-f)llt ·=!Jtto sutaller at·oms. The splitting of an at
fw{Je. am
· energy) wich can be used f
done in a rw.dea.Jt lr.eitc.:toJr..

;.·

(Dr, Fathy Abdel Galil)

- 20 -

Chemistry IGCSE

a. ;;e}()_eo o6 ;;he.U¢ aAOW1d .the nucte.u..b. 2) Ea.c.h llheU c.a.n only c.onto:i.n. a. Li.mUed 1tW11bVT- ofJ e.t.ec.t1Wn.6. 3J The .6heU ne.aJr.e.ll.t :t6 ..the nu.cl.eu.ll 6.il.L5 6JM:t• . When U .W t]u.U, .the e.t.ec..tMn.6 go J..n:to .the nex:t llheU, a.nd .flo on. 4 J · The fJ.iJr.b:t .6 heU c.a.n onty hold :two e.t.ec»to n.6 , .the uc.o nd 8 and .the :t/Wui 8 04 7. 8. 7J

Uec..tMn.6 Me IVUl.anged i.n.

The first twenty eLements in the Periodic Table and their electronic structures

~~e

H I

Li

Be

B:

c

N

0

F

Ne ·

2,1

2,2

2,3

2,4

2,5

2,6

2,7

2,8

Na

Mg

Al

Si

p

s

Cl

Ar

2,8,1

2,8,2

2,8,3.

2,8,5

2,8,6

2,8,7

2·,8,8

K

Ca

2,8,8,1

2,8,8,2

.. ,:2,.8,4

• The outer shell is called the valency shell and the electrons of the outer shel! are the valency electrons. • Elements of the same group in the periodic table contZin the same number ofelectrons iii their outer shelL For example; Jithiunl; sodium and potassium-(group I) have one electron in their outer shell. Fluorine, chlorine and bromine (group VII) have 7 electrons in their outer shell.

_. What is special about· the- nobel gases 7

The nobel gMeo Me; ve:Jty (Uillea.c.tl.ve. They w.i.U not joht up wi..tft ea.clt o.theJr. ;to 6oJUn mo.tec.ul.eo • NoJt wLU .they Jtea.d ea..ll.U.y w.U:h . o.theJr. e.temen..to to {,oJUn c.ompound.o. The nobel gM eo Me .6.ta.b.te (ullltea.c.tl.ve) bec.auJ, e .they ha.v e ·n uU ou.:teJr. .6 heW. We c.oul.cl' c.onctude .tha..t o.theJr. e.t.eme.n.U Me Jtea.c:Uve bec.a.u.!Je .they do not ha.ve {,u.tt llheUb. 'Lt <1 eemb .tha.::t e.f.!'llleJJb, Jtea.d :to f:.Jty a.nd get onf.y 6uU <>hellll. .

:.: ~ .: :

The arrangement of electrons in the first twenty elements . Hydrogen atomic no. 1

"'

l)

H

Helium

He

atomic no. 2

<11

1J

.0

-<

>-

0

0

1

2

.c ....

"' u.

'0

Lithium a10mic no. 3

Li

I

2,1

N

Sodium atomic no. 11

\.U

N'

Nitrogen atomic no. 7

atomic no. 6

N · Oxygen · atomic no. 8

0

Fluorine atomic no. 9

F

atomic no. 10

@ @ @ @ @ @ I Mg

I

2,3 Aluminium atomic no. 13

AI

2,4

Silicon atomic no; 14

j Si

Phosphorus atomic no, 15

. 2, 7

2,6

2,5

P

Sulphur

atomiC no. 16

S

Chlorine atomic no. 17

2,8

Cl

....'-V\

Ar

Argon

atomic no, 18

2,B,2

2, 8, 1

2,8,3

2, B, 4

2,8,5

2,8,6

2, 8, 7

l)

>-

Ne

Neon

(@ ~ (@). (@) (@)(@)@J@»

(/)

u

c

Carbon

atomic no. 5

2,2 Magnesium atomic no. 12

8

Boron

@

@ .....

Be

BeryJlium

atomic no. 4

Potassium atomic no. 19

K

Calcium .1tomic no, 20

Ca

The numbers under each atom show the way the electrons are orranged for that element. This is called its electronic connguratlon.

E Q)

.c

The electronic coftfigura!ion of aluminium is 2, 8, 3. This means it has two electrons in the first shell, eight electrons In the second shell and lhree electrons In the th'~rd shell.

u

2,

o. n. 1

2, 0, 0, 2

2, 8, 8

22

Chemistry IGCSE


Chemical Bonding Ions and Ionic Bonds An ionic bond is formed when one or more electrons is transferred from

an atom of a metal to an atom of a non-metal. Ionic compounds are made up of ions.

Sodium chloride .·(NaCl) Na

.+

(atom)

Cl

(a tom)

2' 8' 7

2' 8' 1

sodium atom

1

chlorine atom

{Na)

{q)

+ Cl- (ion) 2' 8' 8

11 protons

• 11 + electrons u 1 aOverall charge = + 1 10

17 protons 18 electrons

- 17+

• 180verall charge • -1 chloride ion {CI-)

sodium ion {Na•)

Be.c.a!Ue :the· ;,odJ..wn a:tom lw..o LoU:. one. ne.ga..t<.ve. de.c.:t!ton, U be.c.ome.;, a. ·

po<..<.tive. .<.on. Be.c.aLU e. .the c.h'-o!Une. a:tom lw..o ga.J..ne.d one de.c..tJwn. J...t ga.J..n;, a. ne.ga.Uve. c.hM.ge a.nd be.c.ome.;, a. ne.ga..Uve. .Lon •. SodJ..wn c.h'-oJt.l.de. .(.;, ma.de. ofJ IJodJ..wn .<.on;, a.nd c.hloJt.l.de. .Lon;, held .toge:theJL b!f a.n e.!_e.c.Vto.;.ta..t<.c. a.:t.:Ow.c..t.Lon be..tvJe.e.n oppa.;Ue.'-!f chM.ge.d .Lon;,. Ion :

is an electrically charged particle formed from an atom by the loss or gain of one or more electrons.

The. a.Ma.nge.men.t o6 .the. va.J..e.nc.q e.!_e.c..tJt.on;, [.L. e. e!_ecVwn;, o 6 :the ou.teJL.;he.U) i.n :the. .<.o!Uc. compound .;od.f.wn ch'-oJt.l.de. ca.n be Jr.e.pl(.e.;,e.n.te.d a..; 6oUow.;

X X. (2.8.1)

Sodium atom

(2,8, 7)

(2,8)

Chlorine atom

Sodium ion

(2,8, 8)

Chloride ion

- 23 -


Chemistry IGCSE

Magn.el>-Wm oxide (Mg 0)

XX

Mg·:~o~ ~ -xx (2,8,2)

(2,6)

. (2,8)

(2,8)

x)( K

FX

~(·'

Mg:

+

~

(2, 7)

[Mg] 2+

<:x

~ ~F~

(2,8,2)

~

Magnesium atom

(2, 7)

(2, 8)

2 Fluorine

Ma·gnesium

atoms ·.

ion

(2, 8) 2 Fluoride ions

Giant Ionic Structure: [Giant Ionic lattice] This is a regular arrangement of alternating +ve and -ve ions .in ionic crystals, giving strong interionic forces, in other words, ions held together by an electrostatic attraction between oppositely charged ions

This explains the high melting points of ionic compounds. e.g. sodium chloride lattice:

0

Cl

~~~ - ++- +

Properties Of Ionic Compounds:

0

1. They are s.olids and have high m~Iting poi~ts ~nd b~gng points, e.g. the melting point of pure sodium chlonde rs 8 0 . 2 . Solid compounds do not conduct electricity. They[' conducfrt t electricity when melted or dissolved in water, wns are ee o move and carry the electric current]. 3. They are usually soluble in water.

- 24 -

Chemistry IGCSE


Molecules and Covalent Bonds A single covalent bond is formed when a pair of electrons is shared between two atoms (non-metals). Covalent compounds are made up of molecules.

H- H

Hydrogen (Hzl

a hydrogen molecule, H2

two hydrogen atoms

a· shared pair of electrons

Cl

two chlorine atoms

- Cl

a chlorine molecule, Cl 2

88

Similarly,

. Br2'

12,

Fz Hydrogen chloride (HCI) XX

H-0-H

0

H- Cl

xx

H \

Similarly,

PC1

3

/

N

I H

H

- 25 -

Chemistry IGCSE

(Dr. Fathy Abdel Galil) ·

H I

H-C-H -

I

H

)> Draw a d.iagram which shows the arrangement of valency electrons

iJ;I tetrachloromethane [CC4J •

H I

H-C-0-H

Methanol ( CH 0H) 3

I

H

A double covalent bond is formed when two pairs of electrons are shared between two·atoms.

0=0

Oxygen (0 2 )

Carbon dioxide ( C0 ) 2

O=C=O

H Ethene (C H ) 2 ~

\

/

c=c

I

\

H

Chemistry lGCSE

- 26 -


A triple covalent bond is formed when three pairs of electrons are

sha:red~

N

Ethyne [Acetylene}

N

H-C==C-H

c2 Hz

PMpeJ!.tieb a6 Caval.en.t CampoWJ.cU [simple molecular] 1.

Made up of molecules and contains no ions

2.

Do not conduct electricity

3.

Most covalent compounds are gasesandliquids,fewareso[ids.

4.

Covalent compounds are less soluble in water than ionic compo.unds ·•

5.

Usually have lower melting points and boiling points than ionic compounds.

Diatomic Molecules The molecule consists of 2 atoms such as H , 2

o2 ,

N21 Cl , Br , 2 2

rz, Fz.

Allotropes of Carbon Carbon occuts in tw0 solid forms, diamond and graphite. These are very different, even though they both contain carbon atoms. Pure diamond is a l1ard, colourless solid, that sparkles in the light, while graphite is a dark grey greasy solid with a dull shine, When an element has more ·than one form, it shows allotropy. The different forms are called allotropes of carbon.

Allotropes: Different structures of the same element

Chemistr:y IGCSE

- 27 -


Macromolecular (Giant) Structure Diamond

... the centre atom forms lour bonds

.

c

V-UJ.mond .U, a. giant structure o[ caJtbon a.to111<1. Ea.ch caJtbon a.tom ).], joi.ned :to 6oUJt o.theJt. a.tom~ .£.1i a. :t~hedJw.l. aNtangemen.t. Diamond has these properties : 1.

It is yery hard, the hardest substance known. This because each atom is held·in place by four strong bonds. This is vhy diamond is used in drilling and cutting.

2.

It cannot conduct electricity because there are no ions or free electrons in it to carry charge.

Graphite I

1-weak forces

CaJtbon a.to111<1 aJte aiWl:nge.d J.n hex.a.gonb J.n· pa.JrJul..(_el. .lay eM. The .layeM ctl!-e hel.d :toge;thur. by wea.k 6oJtc.u.

- 28 -

Chemistry IGCSE

(Dr~

Fathy Abdel Ga!il)

Graphite has these properties : 1.

It is soft: and slippery vhich feels greasy. This is because the layers can easily-slid over each other. This is why graphite is used as a lubricant.

2.

It is good conductor of electricity. This is because each atom has four electrons, but forms only three bonds. The fourth electron is free to move through the graphite, carrying charge,

·.

Bo-th d.i.amond a.nd gJta.ph.Ue. have. veJr.y IU.gh meLUng po.w..t¢. ThM be.c.a.u.6e. bo-th eoitOJJ,.:t o6 g.la.n.t <>bw.e.twr.e. o6 a..:tom4. Silicon (IV) Oxide

}J,

(Silicon Dioxide}

Silicon dioxide (Si0 ) has a giant 2 structure in which each silicon atom is bonded to four oxygen atoms and each oxygen atom to two silicon atoms.

This structure is similar to the giant .covalent structure of diamond.

u.ke d.i.amond, <>ilieon d..i.ox.i.de .U, luvuf., Ita<> a. IU.gh me..tti..ng po.I.n.:t a.nd dau no-t c.ond!Le.:t e..te.c..tJr.lc.Uy.

properties ofMacromolecules: 1. High m.p. and b.p. 2. Hard [graphite is exception which is soft 1 3. Do not conduct electricity [graphite is exception 1 4. Insoluble in wat~r

Chemistry IGCSE·

(Prof. Dr. Fa thy Abdel Galil)

-29-

Metallic Bond Giant metallic lattice - (In metals)

+ nucleus

0

electron

Giant metallic lattice consisting of the positive ions surrounded by. a "sea" of free (mobile) electrons (i.e. the etectrons ofthe outer shells). >·Metals are good ·conductors for electricity, the current is· carried by the free t;lectrons. > Metallic bonding is very strong in some metals like iron and copper (transition elements) and is much, w~aker as in sodium and potassium (group I).

Summary of Bonding Ionic (be-tween metals and no~-metals)

Bonding

1'------

1

Structures

Giant ionic

I

I

Melting point Conduct electricity ?

Examples

Covalent (between non-metals)

;

High Not when solid, but they do when m:o!ten ! or dissolved in water I I (when i'ons are free I I to move) :'

7

/

\. ·

.,

.

..

T~

Simple molecular I · Giant-covalent · '(macromolecular) Low· 'No

'

Very high

Usually high

No

Yes (has free .electrons)

®8CB8®

~~®~ ®8+8+

I

Ch, h, NH3, C}L, C02, H20

~-J:

>~ Water

I f

Giant metallic

1

. NaCI; MgO, CaC1 2

Metallic (in metals)

diamond, graphite, Si0 2 I

~I !.C ~

~~~ "v~ v'l, Diamond

Fe, Cu, Mg

~

( i·rr ·XX

- 30 -

Chemistry. IGCSE

Topic 4.


STIOCHIOMETRY [Formulae, Equations and Calculations]

.Valency or Combining Power The valency of an element is the .numper which shows its ability to combine with other elements. In molecules (covalent compounds) it gives the number. of covalent bonds which the atoms can form. In ionic compounds the valency gives the charge on the ions of the element.

Valency can be used to predict the formulae of' compounds.

1)

The. Fol!mula.e. o 6 Cova1.en.t Mo.le.c.LLte!> Electron diagram~ ( 1 do·t and cross 1 type diagrams) or just a knowledge of the number of shared electrons in the outer shell can be used to work our formulae.

Complete 'the follow·ing table

Symbol

Va1.enc'y

Carbon

c

4

Nitrogen

N

Oxygen

0

Sulphur.

s

Hydrogen

'H

Chlorine

Cl

Bromine

Br

Ee.emen.t

What are the formulae· of the follwing molecules ·: Ammonia Methane

Hydrogen chlorid.e

........ ......... . ~

Bromine

...................

Chemistry IGCSE


- 31 -

._;_;·

2)

The. FolUnu.C.a.e. o o 1on.i.c Compound& We cannot talk about molecule!! of·ionic compounds. In ionic crystals we have an alternating arrangement of p_ositive and . negative ·ions.

More about ions :

----------------Some elements can lose or gain electrons and change into atoms with positive. or negative charges. These atoms are ··called ions·. Some examples are : Na+ Ca

2+

Cl.,..

..

sodium ion

)(+

potassium ion

calcium ion

A13+

aluminium ion

02-

oxide ion·

. cnlorid~. ion

Spmetimes, groups of atoms can have charges too~ and beh,ave

as ions. The sulphate ion, SO

2-

is made of one sulphur atom 4 and four oxygen atoms, bonded· t.oge'ther; The whole group-of atoms has two nega.tive charges. The nitrate ion,

No 3 - ,

the carbonate ion,

co 3 2- ,

and the

ammonium ion, NH +, are other examples • 4 .Here is a lis't of· most of the ions that you are likely to meet and will need to know :

Valency

I

2

3

Positive ions

Negative ions

H+. u+ Na+ K+ Ag+ NH 4.+ Ca 2+ " .. 2+ Mg. Bal+ Pb2+ Cu-7~. Zn2+ Fea·

hydrogen ion lithium ion sodium ion potassium ion silver lqn ammonium ion •

hydroxide ion • chlo'ride ior, bromide ion iodide ion F- fluoride ion Nol- nitrate ion •

calcium ion magnesium ion ·barium ion iead,,ion copper(II) ion zinc ion irori(II) ion

S2~

FeH Al 3+

iron(III) ion aluminium ion

oHcrBrI-

o2-

so/-

sulphide ion oxide ion· ·sulphate ion

..

col2- carbonate ion •

PO/- phosphate ion

•

(Dr. Fa thy Abdel Ga!il}

- 32 -

Chemlstr)' IGCSE

Predicting the formula of ionic corr Jounds In an ionic cempound, ·th

ions are attracted to each other

-

by their opposite charges. The number of

+ charg.es

is alYays

equal to the number of -charges. Knowing this, the formulae of ionic compounds can be written down. Look at these examples in which the.numbers of positive ions· and negative ions are balanced to make the charges· the same.

·ammonium sulphate

aluminium oxide

magnesium oxide·

this is then written &l .12-l_ Mg ~ Mg~0 2 - - - - - MgO

Remember i) Compounds ending in 1 ide 1 are made of just 2 elements only. ii) Compounds ending in 'ate' have a third element, 'oxygen'.

Question: Write down the formula for each ofthese ionic compounds: 1. sodium chloride 2. aluminium nitrate 3. zinc chloride 4. sodium sulphate 5: copper (II) sulphate 6. zirlc carbonate 7. alllrniniurn carbonate 8. pctassium iodide

9 Cll!ciurn oxide

... ... .. .. ..

10. amrnonium.carbOnate

............

............. ... ... ... ...

11. calcium hydroxide 12. ammonium phosphate

............. ...............

.. .......... ............ ... ... ... ...

1Liron (JII)..oxide.

...............

............ ... -......... .............

16. iron (JII) chloride

............. .:. ...........

17. aluminium hydroxide

.... ·- ··- .....

18.. silver nitrate

.............

~

14~ potassiUI\1 carbonate

15. zinc sulphide

............

(Dr. Fathy Abde! Galli)

Chemistry IGCSE - 33 -

When a che'mical reaction occurs, substances react together. These reacting substances are called tne reactants. They form new chemicals called the products. How to write the equation for a reaction

These are the steps to follow when writing an equation l-

Write the equation in words (word equation).

z~

Now write the equation using symbols. Make sure the· all correct~

formulae are·

3-

th~

Check that the equation is balanced, for each atom in turn;

Make

b~e

you do

no~

change any 6okmulae.

Example l. When hydrogen burns in oxygen or air, it forms water

+

oxygen

H2

+

02

2 H

+

02

hydrogen

2

water

> 2

H H

2

2

o

o

~V!!g111~0 :tha.:t .the c.ommon ga.<>eb (n.Ultogen, oxygen, hydMgenJ and ~lie MlogeM Me dULtom.i.c. Th.U, mean.b .:tlra.t .they .ex..U..:t a.<> motec.ul.eb c.ol1.:ta-i.JU.ng wo
2

Example 2.

IVfaoonesium burns brightly in oxygen or air, it forms magnesium oxide [white powder}: magnesium

+

Mg

+

2Mg

+

Ol)'gen ---7 magnesium oxide

2Mg0

- 34.-

Chemistry IGCSE

(Dr. Fathy Abde! Galil)

Some chemical equations include extra symbols after the formula. They show if the surrstance is a solid (s), liquid (1), a gas (g), or dissolved in water (aq), [aqueous]

sodium

+

water

sodium hydroxide

+

hydrogen

2Na(~

+

2H 2 0(1)

2NaOH(aq).

+

Hz(g)

1. Balance the fo!lowing equations :

+

Na

C[z

-----'?- ••• Na C!

+

c

+

COz

-----'?- ••• CO

A1

+

Clz

-----'?- •.. A!CI,

NO

+

Oz

-----'?- ••• N.Oz

AI

+

Oz

-----'?- .. • Alz O, -----'?-. ... KC!

Mg

+

SOz

+

C!!t

+

2.

COz

+

Ca(OH)

+ ... 0z

+ ... HzO

+

2

Complete the word equation for the above reaction :

. .. . . . . .. .. .. .. . .. . .. . . . ... . .. .. . .. . . . .

+

---'.;>-

+ ........... +

• • • • .. .. • • • • • • • • • • • • ..

..................... -........................ . water

[Dr. Fathy 'Abdel Cali!)

- 35 -

Chemistry IGCSE

Chemical Calculations

Relative Molecular Mass [Mrl Each element has its own relative atomic mass [Ar ]. This is the average mass of its isotopes compared with the mass of- a standard atom of carbon, l~c. Compounds have a relative molecular mass (sometimes called formula

mass). The relative molecular mass (formula mass) of a compound is founq by adding up the relative atomic masses of the elements in the compound according to the number of each element's atoms.

Look at these examples: 1 Sodium chloride, NaC! 1 X 23 1 atom of Na 1 atom of Cl 1 X 35.5 relative molecular mass

2 Calcium chloride, CaC1 2 I X 40 I atom ofCa 2 X 35.5 2 atoms of Cl relative molecular mass 3 Zinc nitrate, Zn(N0 3)z 1 atom of Zn 1 X 65 2 atoms of N 2 X 14 2 X 3 X 16 6 atoms of 0 relative molecular mass

-

-

-

-

23 35.5 58.5

40 7I 111

+

.65 28 96 189

+

+

Calculate the relative molecular masses of the following compounds : l.

3.

Carbon dio:cide,

co 2

Sodium carbonate, Na C0 2 3

Chemistry IGCSE

(Dr. Fathy Abdel Gali!)

- 36 -

Percentage Composition by Mass

Sometimes it is important to know the exact composition of a compound. For example, all bags of fertilizer must show the percentage of the clements nitrogen, phosphorus and potassium they contain on the outside.

The % of an element by

Ar of the element x no. of its atoms

mass a compound in

Mr of the compound

Look at these examples:

1 The % mass of calcium in calcium carbonate, CaC0 3" Ca 40 100 = 40 + 12 + 48. X IOO = C~ + C + 3XO X

=

40 %

40% of the mass of calcium carbonate is calcium.

2 The % mass of nitrogen in ammonium nitrate, NH.N0 3 2X N 28 = X 100 = ZXN + 4XH + 3XO 28 + 4 + 48 X 100

---==---

35 % of the mass of ammonium niuate is nitrogen.

=

35%

X 100

........ .... ,, .. ~

.

.


- 37-

Chemistry !GCSE

THE MOLE

A mo.e.e. (mo.tM. ma.o.6

r o6

any .6Ub.6.ta.nc.e. )_;,

w

Jr.e-

.f.a.:Uve a.tom.Lc. ma.o.6 [Air.) OJt Jtel.a.tive. mo.tec.u..ta.lr. ma.6.6 [MltJ {.<.6 i l .i..6 a. compound) mea.oUJte.d .<.n glUJJn!>.

For Elements :

1.

1 mole of· sulphur • the relative atomic mass in grams • 32 g

.2.

1 mole of calcium = the relative atomic mass in grams = 40 g

For Compounds 1.

1 mole of water = the relative molecular mass of water in grams =2XH+O

- 2 + 16 2.

1 mole of Caco

3

- 18 g

• Ca + C + 3 X 0 = 40 + 12 +'48

= 100

g

mass

No. of

Ar

moles

Mr

or

Questions:

1. What is the mass of one mole of each of the following: a) magnesium

Mg

.................... .

b) copper(II) oxide

CuO·

.............. · · ·

c) sodium chloride

NaCl

............... .

.·-·-·. ·.---.· . ·-·-·.

- 38 -

Chemistry !GCSE


2. What is the mass of

a)

0.1 mole of carbon dioxide (C02)? .......... · - · · · ·

b)

4 moles of oxygen (02 ) ? ................ - · · · · · ·

c)

2 moles of water (H20)? ....... · ... · · · · · · · · · · · · · · · · · · · ·

3. How many moles are there

in:

a)

9 g of water (HzO)? ........ · .. · · · · · · · · · · · · · · · ·

b)

1.6 g of copper (II) oxide (CuO) ? ............ - - · .

c)

117 g.qf sodium chloride (NaCI)? .. : ............ .

d)

9.8 g of sulphuric aci-d (HzS04 ) ? .... - .. · · · · · · · · · ·

e)

20 g of sodium hydroxide (NaOH) ? ............. - .

Avogadro constant [ LJ

.•• is the number of

part~cles

(atoms, molEcules) per mole of any

subs tan.ce • The v:alue of the constant is

A mole of iron (56 g) contains 6 X 10 A mole of A mole of A mole of A mole of A mole of A mole of

23

iron atoms. 23 carbon (12 g) contains 6 X 10 carbon atoms. ~ 23 sulphur (32 g) tontains 6 X 10 sulphur atoms. 23 oxygen atoms (16 g) contains 6 X 10 oxygen atoms. . 23 oxygen mole~ules (32 g) contains 6 X 10 oxygen molecules. 23 carbon dioxide (44 g) contains 6 X 10 carbon dioxide molecules. 23 .. water (18 g) contains 6 X 10 water molecules.

' " ' .'

..... ·•·. --.··.·


- 39 -

Chemistry IGCSE

Moles and chemical equations Not only do equations tell you what substances are reacting and being formed in a chemical reaction, but they tell you the amounts of the substances reacting. The equation·shows how many moles of each substance are reactipg.

Example I

.

magnesiUm

+ hydrochloric

.·magnesium _...,.. chloride

acid

+h

d y regen

Mg(s)

+

2HCI(aq)

MgCiz(aq).

+

H2(g)

this means 1 mole

+

2 moles

1 mole

+

1 mole

and in grams 24g

+

73 g

95 g

+

2g

-

the total mass on the left-hand side of the equation is equal to the total mass on the right-hand side of the equation.

Equations can be used to predict the amount of a substanc,e that will be used up or made in a ch~mical reaction. Look at the examples:

Example2, Consider the reaction between magnesium and oxygen. magnesmm 2Mg (s)

+ oxygen +

02 (g)

-7

magnesium oxide .

2Mg0 (s)

This shows that 2 moles of magnesium react with l mole of oxygen to give 2 moles of magnesium oxide. Using the ideas of moles and masses we can use this information to calculate the quantities of the different chemicals involved. 2Mg (s) 2 moles

2x24 =48g

+

+

2Mg0 (s) 1 mole

lx (16x2) =32g

2 moles

2x (24+16) =80crh

:

...

Chemistry IGCSE


40

Example 3 Lime (calcium oxide) is formed by strongly heating limestone (calcium carbonate) until it is completely decomposed. The equation for the process is:

CaC03 (s)

CaO (s)

1 mole

I mole

=IOOg

•

1 mole

40 + 16 =56g

[40 + 12 + (3x16)]

)>

+

12 + (2x16) =44g

Calculate the mass of calcium oxide formed when 5 g of calcium carbonate are strongly heated.

Pick out the substances involved in the question CaC03 (s) 7 CaO (s) molar ratio:

1 mole

1 mole

mass •

The number of moles of CaC0 3 reacted

5

= -

=

•

The number of moles ofCaO formed= 0.05

•

Mass of CaO formed

=

0.05

100

Mr

why?

= number of moles x Mr

0 o.,:05 =2.8 g =

X

56

.· .. ·..

. ·.· ·:· .

41

Chemistry IGCSE


Percentage Yield Some reactions do not go to completion, i.e. not all of the reactants are converted to products. The amount of product formed in a non-complete reaction is known as the actual yield of the reaction. The amount of product that would be formed if the reaction goes to completion is known as the theoretical yield.

actual yield (given) percentage yield .. -

X

100

theoretical yield (calculated)

Example: On heating 5 g of calcium carbonate, 2.1 g of calcium oxide are formed. Using the information in example 3; what is the percentage yield of the reaction?

>- Sodium reacts with sulphur to form sodium sulphide. 2Na + S -7 NazS An 11.5 g sample of sodium is reacted with 10 g of sulphur. All of the sodium reacted but there was an excess of sulphur. Calculate the mass of sulphur left unreacted. (i)

Number of moles of sodium atoms reacted = .................... . [2 moles of Na react with 1 mole of SJ

(ii)

Number of moles of sulphur atoms that reacted = ..................

= ................... g

(iii)

Mass of sulphur reacted

(iv)

Mass of sulphur left unreacted == ................. g

[4]

, ..

. ·.·- '/

Chemistry IGCSE

42


Molar Gas Volume The volume of one mole of any gas is 24 dm 3 (litres) at room temperature and pressure (r.t.p.). This is known as the molar gas volume. This rule applies to all gases. This makes it easy to convert moles of gas to volumes, and volumes to moles. • Calculate the number of moles a[ ammonia gas, NH3, in a volume of7.2 dm of the gas _.measured at r.t.p.

Volume of gas (dml)

No. of

moles (of gas)

24 dm 3

If the reaction involves only gases,_ then:

The ratio of volumes =the ratio of moles

•

The equaiion for the complete combustion of propane is given below. Insert the two · · missing volumes.

volume of gas/cm 3

1o·

.l> · An excess of hydrochloric ·acid was added to 1.23 g of impure barium carbonate. The volume of carbon dioxide collected at r.t.p. was 0.120dm 3 . The impurities did not reactwith the acid. Calculate the percentage purity of the barium carbonate. BaC0 3 + 2HCl

---i-

Baetz + C0 2 + H2 0

Molar gas volume at r.t.p. is 24 dm 3 • (i)

The number of moles of C0 2 collected

...................

[1)

(ii)

The number of moles of BaC0 3 reacted

...................

[1)

(iii)

Mass of one mole of BaC0 3

................... g

[ 1)

(iv)

Mass of barium carbonate

................... g

[1]

(v)

Percentage purity of the barium carbonate

...................

[ 1)

percentage purity

=

mass of pure substance mass of Impure substance

X

1oo

..·.

- ....

--·----~---

......

Chemistry IGCSE


43

Concentration of solutions The term concentration means the mass of solute dissolved in a certain volume of the solvent. The concentration of solutions is expressed in g I dm 3 or mol I dm 3• For example, the concentration of a solution prepared by dissolving 58.5 g ofNaCl (1 mole) in 3 water to give a total volume of 1 dm3 is 1 mol I dm • On dissolving 2 x 58.5 g (i.e. 2 moles), the concentration is 2 mol I dm3• On dissolving 5.85 g (i.e. 0.1 mole), the concentration is 0.1 mol I dm3 • Remember that 1 dm3 = I litre = 1000 cm3 . )>

No. of moles

Knowing the concentration , The· number of moles solute in any volume ofsolution can be calculated:

Cone. (mol I dml)

Volume · tdm 3 J

Questions: 3

1. How many moles are present in 25 cm3 of 0.1 mol I dm sulphuric acid (H2S04)? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . [0.0025 moles I 2. What is the concentrations of a solutio~ which contains 0.1 mole of solute in 102 cm of solution? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ·· [1 mol I dm I 3

)>.

25.0 emS of a solution of lithium hydroxide, concentration 1. 00 mo!ldrrf3 was placed in a beaker. A few drops of the indicator; methyl orange, were added and the mixture turned yellow. Hydrochloric acid was added from a burette until the mixture just turned red. 20.0 crrf3 of the acid. was needed to neutralise the alkali. Calculate the concentration of the h)'drochloric acid. UOH + HCt ---+ UC[ + H2 0 Number of moles of UOH in 25 cm 3 of a i .00 mol/dm3 solution

- ........................... Therefore number of moles of HCt in 20 cm 3 = ........................... Concentration of HCL = .......................... .

= ........................... mol/dm 3

[4]

[Dr. Fathy Abdel Galil)

-44-

Chemistry IGCSE

Empirical Formula and Molecular Formula

The empirical (ormula of a compound shows the simplest ratio of the number of atoms of the different elements in it, while its molecular formula shows the actual number of atoms of the different elements in it. compound ethane Ethanoic acid

!fiOlecularformula empirical formula .

C2H,; C2H402

..

CH3 CH20

_ICH3C02Hl methane

CH4

CH4

Finding the empirical and molecular formula: Example: A hydrocarbon was found to contain 80% carbon and 20% hydrogen by mass. Its relative molecular mass was 30. Find the empirical formula and the molecular formula. Symbols:

c

H

%

80

20 .

80

20

1. 0.-i.v.<.de.

biJ .the.

a.to mJ..c. mew.; u.

2. Divide by the sma!ler

number

12

6.67

·2o

6.67 6.67

20

to get the ratio:

empirical formula (simplest ratio): Find mass of empirical formula: ·Compare with M,: Molecular formula must be twice ·empirical formula;

molecular formula ts:

6.67

:

3

CH3

12 + 3

15 } M, is twice mass of 30 empirical formula

""

;._;__

.· ..· ... ·.. : .

.

Chemistry IGCSE


- .4-5-

Questions __: c:::•--...:c;_..,...,

1, The M, of oxalic acid is 90 and ifs composition by mass is: carbon= 26.7% (i)

hydrogen =2.2%

oxygen= 71.1%

Calculate the empirical formula of oxalic acid.

'••

................. ·-·····. ·······-. -· .............................. -··· ....... ······-····· ··········· .............................

·············· .......................................... ······························································· ........ [3]

(ii) What is the molecular formula of the acid?

·················································································-~·:········································-[1]

2.

The hydrocarbon benzene has an empirical formula CH and Its relative molecular. mass Is 78. What Is its molecular formula?

..................................................................................................................................... .........................................................................:....................................................[2]

-46-

Chemistry IGCSE

(Dr. Fa thy Abde! Gal if) ·.·.

Topic 5.

THE PERIODIC TABLE

The periodic table is obtained by arraneing the elements in order o£ increasing atomic number and piacing them in rnws so that similar elements fall into vertical columns. The horizontal raws are called periods and the vertical columns are called groups.

GrCKlp1

·L

11;

Ill

1

en

""' ""' ''

VI!

0 ,----,

c

N

0

f'

Ne

AI

Sl

p

s

C!

Ar

Zn

Gt

Ge

As

Se

Br

Kr

Ag

Cd

In

Sn

Sb

Te

I

Xc

""

Hg

T!

Pb

Bl

Po

"'

Rn.

Be

3

N•

Mg

4

K

G.

Sc

Ti

v

Cr

Mn

Fe

Co

Nl

Cu

5

Rb

Sr

y

Zr

Nh

Mo

,.

Ru

Rh

Pd

6

c.

n.

u.

Hf

T,

w

Re

Os

lr

Pt

7

f'r

R2

Ac

,,

VI

n

Ll

0

V

l!e

2

tundtlon ttit.tlh

"d

_.,;

IV

H

Metals take up tlte part of the periodic table to the left of the hefiVJ' line. 1.

The periodic table showing the division into ·metals and non-metals. The clnsa of eiernents whi"ch lies on the borderline batween me!=als and non-metals is often classified as .o_em.(.-me;ta.t6 or me;tallo.{.dh 1 e.g. silicon, arsenic, germanium.

Fait examp.te,

aJr..~>e!U.c. {M l

.too/u, .Uk.e a. me.ta..t, .{..e . .oiU.ny bu;t

doe.o no.t belutve a..o a. me.ta..t. He

H

"_:It,._,_ · .,.<.'1 o.z

Non - > -

~~ o-'0::: melols o· r 'a;q.. q.~• ~

~------c--Melols---------1>-

.t~

?J,..:

'>j.·. ".>0 \ ~01.

~oy.. :.r

2.

Elements of the same group have similar properties (the same no. of electrons in the o.utershell).

-47-

Chemistry IGCSE

3.


The valency (combining power) increases with_the group till eroup -4, then decreases.

4.

Group number

1

2

3

4

5

6

7

0

Valency

1

2

3

4

3

2

1

0

The reactivity of metals increases down a group Rb

5.

> K > Na

The reactivity.of non-metals decreases down a group

-

'·

> Br > I

F > Cl 6.

> Li

Metals react with non-metals to form ionic compounds. Non-metals either join with other non-metals. to make

:C{)I!.!I.te:n;t.

C:am)'JoWttll. or with metals to make .0J11ic. c.ompaund6.

Relation between group number and number of valency electrons.

I

II

u•

Be

0 ,.---

0

N•• M~·

K•

c.'•

Fe1+

He

III

IV

v

VI

VII

B

c

N

o'-

p-

Ne

!Jl+

Si

p

s'- a-

Ar

Br-

Kr

.Cu2+ Znl+

I-

Ag•

Ba 2 +

Pbl+

r

-~

Group I elc:mcnt5. all h:ave l electron to lo$e from their outer shells. They form + ions.

I

Group '\_'II elements h1ve 1 electrons in their outer 'hells.· They need to gain one electron to.fill their outer Shell and form 1 ne&:uive ion.

Group II dement' lll h:rve 2 electrons; in the: outer .dlell. They form 2'*' iOJ'lt..

Group VI dements hne 6 elcciron11 in their outer s:hcl!s..They need' to gi.in 2 dcctron~> to

Group lll dementt have 3 dectroos to lose. They (arm 3 ~ ions:.

fUI their

shell~. They

form 2- ions:.

'

-48-

Chemistry IGCSE


Group I elements: the 'alkali metals' Density

Melting point

Name

Symbol

Lithium Sodium Potassium Rubidium Caesium

Li Na

1.

K

Rb Cs

rc

fgcm-J

180

0.53

98

Group lions Lithium ion

u+

0.97

Sodium ion

Na+

64

0.86

Potassium ion

K+

39

!.53

29

1.90

Rubidium ion

Rb+

Caesium ion

cs+

They are called th!'. alkali metals because they react with water to form alkaline solutions.

2.

The outermost shell contains one electron.

Where are Group I metals found? The. me..ta.to .thi!Jil!>e..tvu do na.t ac.c.wr. .<.n na..twr.e.. The.£{ Me. .tao Jr.e.a.c.tive.. The.Jr.e. Me. Ve.lt.IJ many c.ompouncU a6 GJr.aup I me..ta.to Sodillm c.htoJr..{.de., NaC.t, ~ .the. mo~.t c.ommon GJr.aup I compound. The. MWLc.U o 6 NaC.t Me. : a) S e.a wa.te.Jr. · 6) GJr.aund '.Jr.Oc.k: ~aLt·· de.po.oill.

Properties of Group I elements

PhysiCal Properties

The metals .are easily cut with a knife.· Metals further down the group are softer.

Soft and shiny when cut

Conduct electricity

rodium.

Low density

The metals are ail very good ciectrical conductors.

'

I

r The metals all have low densities. Lithium is the lightest metal known. Lithium,. sodium and potassium. all float on water. This is because tliey are less - dense than water.

(Dr. Fa thy Abdel Gall!)

-49-

Chemistry l GCSE

Chemical properties : very reactive metals Reaction with air:

The metals are stored under oil. This is because they react with air. ·

The metals are only shiny when freshly cut. They quickly tf!rnish as they react with air.

Metals all burn easily in air e.g:

ssdium

+

4Na(s)

+ 0 2 (g)

potassium

Reaction \vith water

+

OJeygen

sodium oxide

oxygen

--->-potassium oxide

Metals all react easily with cold water to form alkaline solutions.

The heat from the reaction melts the metal as it reacts:

sodium

+

water

-+

sodium hydroxide

+

hydrogen

2Na(s)

+

2H 2 0(!)

-+

2Na®H(aq)

+

Hz(g)

potassium

+

water

-+

potassium hyclraxide

+

hydrogen

2K(s)

+

2H 2 8(!)

--+

2K@H(a<'J)

+

H2(g)

The ob<. vr.va.:t.i.ort.O .tha/: c.a.n be ma.de when a. <>mill )!li.ec.e o 6 .the a.tka..U. meta.t i.<> a.dded .to a. :t:Jta U!J h 0 n wa:;{:eJt : 1. UthWm fi.tow a.nd a. ga.<> 6/-zze<> Mound d. Z. SocLWm 6.tow, meW 1J..!> d ;,hoot<> a.c.Jr.OM .the wa;tvr. a.nd a. ga.<> (i.zzu 6a.<>.t. 3. Po.tM<.i.um Jtea.W v.<.o.ten:Uy .tha/: d me.t.t<> .<.mmedi.a..te.ty a.nd c.a..tc.hu 6.0te.

-50-

Chemistry !GCSE

(Dr. ·FathY Abde! Cal ill

Reaction with chlorine: metal

·~ chlorlne---->-gas

\

·

~

1"'~~'--~_,\.:>.~-CQ-";...n_..,..IL._ __...,l$j~ ~

_,_tofume cupboard

..

Reactivity of Group. I metals

heat

Lithium

The metals react easily to form chlorid"'>:

Sodium Potassium

lithium 2Li(s)

+ +

chlorine Cl 2 (g)

-+ -+

· lithium chloride 2LiCI(s)

sodium 2Na(s)

+ +

chlorine

-+

Cl 2 (g)

-+

sodiuni chloride 2NaCI(s)

potassium 2K(s)

+ +

chlorine Cl 2 (g)

-+

Rubidium

n

Caesium

potassium chloride -+ 2KCI(s)

So you can see these Group· I metals have similar properties. Lithium is said to be the, least reactive of them, because it reacts the most slowly".· Potassium is the most reactive of the three.

Why they. ha.ve. ·~.i.mliaJI. pltopeJt.;U~ ? In the elements of Group I, all the atoms have.! electron in the outer shell. That is why· the elements hehave"in a similar way.

Elements behave in a similar way if" their atoms have the same number of outer-shell electrons.

Group I compounds Metal

Chloride

Bromide

Nitrate

Sulphate

Carbonate

Lithium

LiCI

LiBr

LiN0 3

Li 2 S0 4

Li2 C03

Sodium

NaO

NaBr

NaN0 3

Na 2 S0 4

Na 2 C0 3

Potassium

KC)

KBr

KN0 3

K2 S0 4

K2 C03

GJtoup r ~a.Lt6 {c.he.o:Ud~ I n..UJr.n.;t~ I c.aJtbona.te..o 1 e..tc.. J ivte. w!U.te., .<.o n..Lc ~ o.Udo, M.f.u.b.C.e. .i.n wate.Jt. [giving a colourless solution]

metals get more reactive

Chemistry IGCSE

- 51 -

Transition Elements

e.g.


Cu, Fe, Cr, 1'-!i., V., Co.·

Typical characteristics of transitipn metals ; 1.

They

.~re

metals of high melting points (exceP.t Hg) and densities

(hard, strong).

2.

They.form colou_red compounds, e.g. copper (II) ions,Cu iron (II) ions, FP.

:;,

4.

2+

2+

(aq) are blue,

(aq), are green.

Host of them have more than one valency, 2 3 different charges, e.B. Fe +, Fe +.

i.e. forming ions with

The metals and their compounds can act as .catalysts a)

Iron ·.is used in the m
b)

V~nadium

(V) oxide is used in the manufacture of sulphuric acid.

Compa:tr.e. .the. .phy¢-i.c.a.l a.nd c.he.mi.c.a.l p!topeJU;{.eo bU:ween. pa.tM.t,.{.um (gJtOap I

me.tall a.nd va.na.d.wm

(bw.tt.~>.uion

Potassium

me.ta.e.l.

Vanadium

(Dr. Fathy Abdel Ga!H)

- 52-

Chemistry IGCSE

Group VII Non-Metals the Halogens

D c.o.e.oUJr. bec.ome..t. daltkvc.

·Halogen Molecule State at

Colour

room temperature · Pale yellow

Symbol of Halide ion

F

-

CI

Fluorine Fz

Gas

Chlorine Cl 2

Gas

Green

Cl

Bromine .Br2

Liquid

Red-brown

Br

Iodine

12

Solid

Dark gr.ey

I

Astatine

At

2

...

...

F

-

-

Br I

. ..

+ '=fry mcreaszng

>-Bromine is very volatile [has low b;p. 59°C}. This means ihat it easily turns into a gas. >-

Iodine is a dark grey solid, when warmed, it turns into a purple vapour [it sublimes]-

>-

Aqueous solution of iodine is brown. The halogens all exist as diatomic molecules. The tWo atoms in the molecule are joined by a covalent bond. Cl

- Cl

. a chlorine molecule, Cf2

Uses of Chlorine: • Making bleach .. In water purification [kills bacteria] "' Maldn;; PVC (insulation for electric wires)

..

-53-

Chemistry !GCSE

(Dr. Fa thy Abdel Galil) ·:·:

Chemical Properties .

Reaction with .metals:

Halogens react wi~h. most metals to make salts:

+ +

sodium 2Na(s)

Reaction with.indicators:

-+ -+

sodium chloride 2NaCJ(s)

Chlorine gas dissolves in wa\er to make a powerful bleach. Damp indicator paper is quicldy bleached with chloiine., . -Test for Cl

Displacement reactions:

chlorine Cl 2 (g)

2

gas :

Chlorine bleaches damp litmus paper.

Chlorine can displace bromine and iodine from a solution of their salts: chlorine gas-·===\\

v ~I>Otassium Iodide solution ·1oame belng forroed

chlorine

+

Clz(g)

+

potassium -+ iodide 2KI(aq) __,.

[colourless]

Ionic equation:

+

Clz

. chlorine

+

Cl 2 (g)

+

zr

In o:thvr.

WOJtd.l,,

Clz

7

potassium -+ bromide 2KBr(aq). -+

[colourless]·

ionic equation:

->

+

2 Br·

-> 7

iodine

+

I,(aq)

+

potassium chloride 2KCI(aq)

[.brown]

Iz

zcr

+

bromine

+

Br,(aq)

+

potassium chloride 2KCl(aq)

[red]

Brz

+

zcr

a. mOJte Jtea.c:Uve hai.ogen w.Ut dUp.f.a.c.e a. leo<> Jtea.c:Uve ha..e.ogen

t)Jtom ffi compound;,.

Halogens have similar properties because their· atoms all have 7 electrons in. the outer shell.

-54-

Chemistry I GCSE

(Dr. Fathy Abdel Gs!il)

Nobel Gases :

Helium, Neon, Argon, Krypton, Xenon 1.

The nobel gases in group 0 are very unreactive (inert), they have complete outershell of electrons.

2.

They do not usually form compounds and exist as isolated single atoms (i.e. monoatomic).

neon etomi"::\\\

~((G

N•

hollum atocn• ·-<--__. He

Uses of Nobel Gases 1. Helium is very light and. does not burn, so it is used in ballons and air ships.

HqdJtogen hqdJtogen

WCL6

601t

£L6ed .Ut .the pa..o.t in ba.Uo/1..6, now hel..Wm Mpl.ac.ed 6-UUng ba.Uo/1..6. Whq ?

••••••••••••••••••••••••v••••••••••••••••••••••••••••••••• .. •••

2.

Argon

i~

for

fil1~ng_electric

light bulbs as an.inert atmosphere

It is very unreactive and-helps protect the filamenc,

tung5ten

filament

3.

argon

Neon : When an electric current is passed through neon gas, it gives out a bright light and is used in lamps and advertisement signs.

-55-

Chel)listry I GCSE


Test for Gases

Test

Result

Hydrogen

Lighted splint

Burns with a pop

Oxygen

Glowing splint

Relight:s

Carbon dioxide

Limewater

Turns milky

Chlorine

Colour

Yellow-g'reen

Damp litmus paper

Bleached

Ammonia

Smell

Pungent

[ttlkq.Une gcw l

Damp red litmus

Turns blue

Formula

Gas

paper

Collection of Gases gas l.

-l-i>'

Upward delivery over water : For gases which are insoluble !n water such as H , 2

2.

o2 and N2 •

Downward delivery : For gases which are soluble in water and denser than air

3.

Upward delivery For gases which are soluble in water and less dense than air such as NH .

3

H [Ughte;c than Wr.) Mn be 2 a-Uo c.oUec.ted bif up.wJtd deUveJty.

gas __,.._

gcw-jM

-56-

Chemistry IGCSE


Drying of Gases 1.

Gases that do not react with acids such as·

co 2 , so 2

by pasa_ing it through concentrated sulphuric acid

may be dried

[dAy.i.ng agent].

11uestion :

~-""""'""'""'""'-=--

W/Uch o6 .the. 6o.UoW-Wg cuur.angeme.n.tl> 6oiL dJty,~ng a. gaJ, w.Uh concen:tJur;te.d a.cJ.d )!, co!LILe.c.t f 2

1

~===:;, r;=='d=r=y==~

concentrated sulphuric acid

concentrated sulphuric acid

2. Ammonia gas is dried by passing it over solid calcium oxide [drying agent]

>- [Conce./Lt!ta.te.d .sul.phU)()_c a.c<.d

ca.nno.t be.

tt<1 rid

be.ca.W, e. U 1r.e.aw

wUh a.mmoiUa. gaJ, .] ammonia

+ sulphuric add

-----+-

nmmonlum sulphate


-57-

Chemistry IGCSE

Oxidation and Reduction copper(II) oxide

excess hydrogen burning in air

[black]

·ice water When hydrogen is passed over black copper(II) oxide in the apparatus above, the blnck powder turns pink~brown (copper) •

,.._ . What is the purpose of the ice?

reduced.

1

oxidised.

I

copper( II) oxide· + hydrogen

+

CuO(s)

-7-

copper + water Cu(s) ·

H (g) 2

+

H .0(g) 2

Re.due-Utg ,a.ge.n.t

The copper(II) oxide is losing oxygen. It is being reduced. The hydrogen is gaining oxygen. It is being oxidised. In other words:

> Oxidation is defined as the addition of oxygen. )>

Reduction is defined as the removal of oxygen. Reduction and oxidation always take place together in a reacticn. So the reaction is called redox reaction.

Question: Which substance is oxidised and which is reduced in the following . reactions, mention the reducing and oxidising agents.

----7 2Fe

Common reducing agents

hydrogen, carbon,

+ 3CC)z

:

carbon monoxide,

reactive metals

-58-

Chemistry IGCSE

(Dr. Fa thy Abdel Ga!i!)

)> Since hydrogen is a common reducing agent, the addition of hydrogen is a reduction reaction, and the opposite, i.e; removal of hydrogen is oxidation. In which change shown has nitrogen been reduced?

B nitrogen, N2

c

~----------~

N02

D

)> Redox in terms of electron transfer [01 L]

[RIG]

Oxidation

Red·uction

Is

Is

Leiss of electrons

Gain of electrons

From the definitions above, it follows that:

Reducing agents give electrons. Oxidising agents accept electrons.

Consider the reaction of magnesium with oxygen : magnesium

+

oxygen·

--+

magnesium oxide

2 Mg

+

02

~

2 MgO

The ma.gne;,.I.wn ).), oudA.ud a.nd .the axyge.n ).), Jte.du.cvi. Vwring .tw Jt.e.a.Ul.ott, .two el.ecbw 111> a.Jt.e. .til.aiU 6e.Med filtom ma.g lteJ>.i.wn .to oxyg e.n. Ma.gne;,.f.wn I.on a.nd oude ion aM 6oJtmed.

0 +

Mg

2+ Mg.

2 e

oz-

+ 2 e

Ma.gne;,.f.wn, w/U.c.h ).), oufued, .to~>e;, el.ectJto111>; oxygen, w/U.ch ).), Jte.duc.ed, ga.i..1u el.ectltoJ1-6.

-59-

Chemistry IGCSE


Oxidation States [Oxidation Numbers] The oxidation state of iron in iron(II) oxide is 2 and in iron(III) oxide is 3. The oxidation state of manganese in manganese(IV) oxide is 4 and in · ·potassium manganate(Vll) is -7. The oxidation state of chromium in chromium(III) oxide is 3 and in potassium dichromate(VI) is 6.

Change in oxidation state )>

Oxidation involves an increase in oxidation state, e.g.

)>

Reduction involves a decrease in oxidation state, e.g.

Oxidation and Reduction [summary] with respect to: O!fgen hydrogen electrons oxidation state

oxidation addition of oxygen removal of hydrogen I loss of electrons [OILJ . increase in oxidation state·

reduction removal of oXygen addition of hydrogen gain of electrons [RIG] . decrease in oxidation state -

Tests for oxidising and reducing agents a) Oxidising agent (oxidant) + potassium iodide solution The colour changes from colourless to brown [h]. b) i. Reducing agent (reductant) +.·acidified potassium magnate (yii) solution : The colour changes from purple to colourless. ii. Reducing agent (reductant) + acidified potassium dichromate (VI) solution : The colour changes from orange to green.

- 60-

Chemistry IGCSE

Topic 6.


ELECTRICITY AND CHEMISTRY [ELECTROCHEMISTRY]

Conductors and Non-Conductor:; Solid substances that allow electricity to flow through them nre

called conductors, All metalo are good conductors of electricity. why., Substances that do not allow electricity to flow thr·ough them are called non-conductors or insulators. All non-metal aubatancea such as glass, plastic, wood, and-rubber

ar~

insulators. There is, how-

ever, one very important exception, Carbon, in the form of graphHe, is non-metal, but a very good conductor of ele.ctricity. why ? Semi-Conductors,

They are substances which contain no "free electrons" and no "ions" bu·t allow very small cunerit ~O··'pass through them, i.e. they conduct weakly e.g.

c,Wc.on. ·

. Electrolytes and Non-Electrolytes :

. Liquids that conduct an ele.ctric cun:ent are called electrolytes. Those that do not conduct are called non-electrolytes. Electrolytes are substances that contain ions which are fi:ee to move about, so they are ionic compounds that are molten or are dissolved in water, Covalent compounds such as ethanol, pure water.or sugar solution are non-electrolytes. The following figure shows the apparatus that could be used to see if a liquid is an electrolyte .

.-----1

F

a battery A lamp. If it glows, electricity must be flowing through the liquid.

electrode called cathode 8

electrodes. Generally made of graphite or :::::::H-+--1 unreactive metal like platinum

<±) electrode called anode

.:.

liquid under test ::'

-61-

Chemistry IGCSE

Typ~:

free moving wns

)>

of su~srtmce _

(Dr. Fa thy Ab<.lel Galil)

Electrolyte

solutions of acids and alkalis in water

,J

solutions of salts· in water

,J

molten salts

,J

Non-electrolyte

ethanol petrol sugar solution pure water

,J ,J ,J

oil

,J

,J

Electrolysis :

Electrolysis is the decomposition [breakdown] of a substance by electricity. ':·

During electrolysis, ions migrate towards the opposite electrodes. )>-

Can you suggest why -ve ions are called anions and +ve ions are called cations? ........................................... .

.. ! .

. ••••••••••••

0

0

0

••••••

0

••

0

•••••••

0

0

•

0

••••

0

•••• ' •••••

0

•

0

0

....

Chemical changes take place at the electrodes. At the cathode, +ve ions gain electrons and become -atoms or molecules. At the anode,. -ve :!:ons lose electrons and become atoms or molecules.

The electrons flow in the external circuit from the anode into the cathode. a battery

r-~--t'I t------, electron flow

electron flow

e

cathode ·.

:_·anode

(£)

·negative ions lose electrons at tho"· anode

electrolyte

.

.,

/

-62-

Chemistry IGCSE

(Dr.FathyAbdel Gali!)

Electrolysis of Molten Substances using Carbon Electrodes The compounds are decomposed into their elements. The rules for the . electrolysis of molten compounds are : Molten Compound •::

At the anode + Non-metal

At the cathode Metal

> Electrolysis of molten lead bromide [PbBr2] +

-

a battery ;.·

carbon anode +

carbon cathode -

bubbles ~F brown gas {bromine)

dlr.ap.5 a 6 moLten lead ·(gJte.y} .

~··.

-

molten lead bromide

t

heat

>:Explain. why the lead bromide needs to be melted for electrolysis to .

:take place ........................... ·.................... .

> The. electrode reactions are summarized as follows : Electrolyte Lead bromide, PbBr2

At the cathode Pbt+ + 2e- ~ Pb

At the anode + 2Br- ~ Brz + 2e·

> Complete the following table: molten electrolyte. lead bromide sodium chloride . magnesium fluoride aluminium oXIde

Product at cathode lead .. . . . . . . . . . . . . . . . . . . . . . . . .... . . . . . . . . . . . . . . . . . . . . . . ..

· Product at anode bromine

t-

................... ..................

...................

-63-

Chemistry IGCSE

[Dr. Fathy Abdel Galil] ..-._

Electrolysis of Concentrated Uydrochloric Acid: · At the anode +

At the cathode -

Electrolyte

.

2W (aq) +

Hydrochloric acid, HCI (aq)

2 e- -7 H2 (g) 2Cr (aq) -7 Ch(g) + 2e··.·.

Electrolysis of Aqueous Solutions: · The products of electrolysis of aqueous solutions are difficult to predict than molten compounds. This is because as well as there is a cation and a anion from the salt, there is a cation (H") and a anion (OH) from the water.

Electrolysis of Concentrated Aqueous Sodim Chloride :[Brine} : At cathode. ~

Atanode +

,___

__.---,

LNa+ - - - - - _ --- \ __ d-;

FromNaCL

-- oH_., /

-~

1r '

~-,--

·..-.+ ' , ~

-- --

---

I

,

--" Only F takes part in electrolysis [H being lower in the reactivity ·series than Naj

I2 F

(aq) + 2 e· -7 H 2 (g)

.

f

-- --J Only Cr takes part in electrolysis because it is present in much greater concentration than OH

jz Cr{aq) -7 Cl2 (g)'+ 2 e·

/

This leaves a solution containing sodium and hydroxide ions (a solution of sodiwn hydroxide, NaOH). The solution is alkaline (i.e. turns red .litmus paper blue). Compare the products of e./ectrolysis of: (i) Molten sodium chloride (ii) Concentrated aqueous sodi!fm chloride )>

-64-

Chemistry IGCSE


Manufacture of Chlorine and Sodium Hydroxide : The method is based on the electrolysis of concentrated aqueous sodium chloride (brine)•. brine

chlorine

lui~_____;

...

..... ...

.·.·. ·•· ~

pos!Uve eleclrodo

aqueous sodium hydroxide

neg alive

elec[rode

Predicting the Products o[Electrolysis o[Aqueous Solutions :

)>

)>

At the cathode If the metal is higher than hydrogen in the reactivity series, then hydrogen gas is produced If the metal is lower than hydrogen in the reactivity series, then the metal is deposited (formeq}.

The reactivity series

Na Ca Mg AI Zn

above hydrogen, so hydrogen gas is evolved at the cathode

Fe Pb Cu

Ag least reactive

Au

below hydrogen so metal deposited at the cathode

)>

)>

At the anode + For concentrated solutions of chlorides,· chlorine gas is produced For sulphates and nitrates, oxygen gas is produced

-65-

Chemistry IGCSE


Electrolysis of Aqueous Copper(ll)sulphate : Using carbon electrodes (i.e. inert)

-{ Cu +) ....

--so - -- ----'

• - ..:- 1

....

--· -· -· ·

2

FromCuS04

Atanode +

~

Atcathode

... -

2- I

4

\.-- /

1-

....

,rr\-·-·

FromHzO

I

/ 10Ir' 'r

-----

Onlythe copper ions take part in the electrolysis.

Only the OH ions take part in the electrolysis.

Cu 2+ (aq) + 2e· -7 Cu (s) Copper deposited on the cathode (as brown deposit)

Oxygen gas is given off

The solution left is dilute sulphuric acid (H2SO_J. )>

The solution changes from blue to colourless I I

2) -

cathode

anode

+

I

0

.. b~r.own 0

de.po.oU

6 c.o ppe.IC.

'

0

c

'

bubbles of oxygen

6Oc_ c.oppe.IC. (II) .;ul..pha..te. M.fu:ti..o n

Summary: Electrolysis of :;:tqueous copper-(II) sulphate:

atcathode copper

The solution left is dilute sulphur~ acid (H2 S04).

atanode + oxygen


-66-

Chemistry IGCSE

'•;

Types of electrodes : . Inert electrodes: Carbon (graphite) or platinum,. They do not take part in the electrolysis.. Active electrodes: e.g. copper, silver, zinc, nickel. They take part in the electrolysis and the active metal anode dissolves, (i.e. passes into solution as ions. In other words, the mass of the active· metal anode decreases).

Electrolysis of Aqueous Copper(II)sulphate : . Using copper electrodes (i.e. active) .

I,

ll

~ copp er caih ode -

copper an·ode +

1...

-7 Cu2+

-7

-7 Cu 2;-

vaqueo us copper(II)sulpltate """~........ (blue)

Atanode +

Atcathode -

Copper passes into solution as ions (i.e. the anode dissolves) [anode: decreases in mass] [ Cu (s)

~

2

Cu + (aq) + k

J

Copper deposited [cathode: increases in mass]

I Cu2+ (aq) + 2e-

~

The aqueous copper(ii) sulphate remains unchanged.

Cu (s)

I


-67-

Chemistry IGCSE

Application of Electrolysis: 1} Refining of Copper: Copper can be refined by electrolysis using a block of impure copper as the anode and thin sheet of the pure copper as the cathode. The electrolyte is aqueous copper(II)sulphate. Impurities sink to the bottom of the container as anode sludge. The overall result is the transfer of copper atoms from the impure copper to the cathode. );>

·EB

e

an. ode.

cathode. pU/tl!. CO(I(Il!./t

cop.fll!./t( I I ).out.phai.e. .oot.uil.on.

Zinc can be refined by electrolysis. The method is similar to that used to refine copper. Complete the following statements. about refining of zinc. The cathode is made from ................................. . The anode is made from .................................. . The electrolyte is aqueous ................................. .

2) Electroplating: Many metal objects are electroplated for: a) Protecting them from corrosion and rust b) Making them look attractive

anode: _ _:::,-

cathode: (object to be plated)

(metal used to plate the• ::>bject)

·='='""='!-·electrolyte:-

aqueous solr.{tion contairzing.ions of the plating metal

if the object is to

be plated with copper silver .nickel

· the anode will be made fro in copper silver nickel

the electrolyte will be aqueous copper(II)sulphate aqueous silver_nitrate aqueous nickel sulphate .

I

Chemistry IGCSE

-68-

[I?r. Fathy Abdel Galil]

3) Extraction of metals Reactive metals above Zn in the reactivity series such as Na, Mg, Ca, AI can be. extracted only by electrolysis.

Extraction of Aluminium Ore: Bauxite. The purified bauxite (aluminium oxide, Al 20 3) is electrolysed in molten cryolite (Na3A1F6). Aluminium oxide has too high melting point to be used on its own, so it dissolves in molten cryolite at 900°C (i.e. cryolite is used to lower the m.p. ofAl1 0J)

....

Carbon anodes (";), --~,;,.,o."'l"""___ 1±/

Molten electrolyte -HI-(aluminium oxide

fil!.-l~·carbon

lining .ofccll(cathodc)

dissolved in cryolite) ·

At cathode-

The aluminium sinks to the bottom.

8.

..

AI

At anode +

Oxygen gas is produced.

.> As the hot oxygen escc·.pes, it burns away the graphite anode· ( C + 0 2 7 C0 2), ard so they have to be replaced from time to time. .> Making aluminium is an expensive process because large amounts of electricity are needed.


-69-

Chemistry IGCSE

Topic 7.

. ACIDS, BASES AND SALTS

Acids: An acid is a substance giving hydrogen ions, II'" (aq), in aqueous solutions. Aqueous solutions of acids tUrn the colour of litmus red. It is the hydrogen ions that cause the change of colour. Remember that the hydrogen ion is simply a proton. . In other w.ords, an acid is a proton donor. .. ·common acids:

strong

Acid

Formula

Hydrochloric acid

HCl

Nitric acid

HN0

Sul.phur:Lc acid

{ weak <-- Ethanoic acid (Ace tic acid)

Ions present in the acid

--

[ehto.!UdeJ

H+

Cl

H+

NO;

[ JU.:tJut.te l

H so 2 4

2H+

so 2 -

[.o ul.p fta.te J

CH COOH 3

H+

CH COO 3

3

4

-

[ e..t!ta.noa.te J-

Basicity of acids: · Monobasic such as HCI, HN03 , CH3COOH such as H2S04 Dibasic.

Reaction of acids l.

f:cids reac_t. .with reactive metals to give a sa·lt and hydrogen

acid

+

metal

salt

'+

hydrogen

dilute sulphUiic acid

magne>lum ribbon

magnesium Mg (s)

+ ,sulphuric acid +

H2SO.~

(aq)

--r.

magnesium sulphate

___,. · MgSO.~ (aq) + Hz (g)

ionic equation:

Mg (s)

+ 2H+ (aq)

------'Jr

Mg+Z (aq) · + Hz (g)

+ -hydrogen

- ro-

Chemistry IGCSE

2.

(Dr. Fathy Abde! Galil)

Acids react with bases (metal oxides and hydroxides) to give a salt and water [neutralization]

Acid

+

Salt

Base·

+

Water

dilute rulphuric acid

·:.

heat

sulphuric acid H 2 SO,(aq)

+

ccpper(ll)

--+-

oxide

+

CuO(s)

--+-

b.t.a.ck

b.fue

Sulphuric acid + sodium hydroxide H

3.

2

so 4 (aq)

copper(ll) sulphate CuSO,(aq)

+ 2 NaOH(aq)

~

Na

2

+

water

+

H2 0 (I)

sodium sulphate + water

so 4 (aq)

+ 2 H 0 (.f) 2

Acids react with metal carbonates to form a salt, carbon dioxide and water ·acid

+

carbonate

--+

salt

+

water

+

carbon dioxide

+

calcium carbonate CaCO,(s)

--+

calcium chloride CaCl 2 (aq)

+

water

+

+

H 2 0(!)

+

carbon dioxide C0 2 (g)

dilute

hydrochloric acid 2HC!(aq)

>-

'

T

--+

Thing to remember about hydrochloric acid: Hydrochloric acid is a solution of hydrogen chloride gas in water. water HCl (aq) HCl (g) [covalent] [ionic]

•:':·

-71-

Chem_istry JGCSE


Bases A base is a substance that can accept hydrogen ions, i.e·. a proton acceptor.

Ox..i..du, and hydJr.ox..i..deh of metals are bases. Properties of bases :

1.

·Bases react ,;ith acids to form a salt and ,;ater only (see properties of acids), This reaction is called neutralization reaction.

2.

If a base is soluble in ,;ater, the solution is called an alkatl.

An aiH;ali is a base that is soluble in water

-

'

Common alkalis : ·Alka-li

,crong { weak

Formula

Ions present in the alkali

Sodium hydroxide

NaOH

Na+

'"'"'''= "''""""'

KOH

K+

Calcium hydroxide

Ca(OH)

NH (aq) or 3 NH 0H

f-- Aqueous ammonia

(often called ammonium hydroxide)

3.

2

OH

-

20H OH

Ca 2 + NH+

OH

4

4

Solutions of alkali turn the colour of lit"mus £~~~It is the hydJr.ox..i..de. ~OM that cause the chang.e of colour.

Weak and strong acids and bases Acids strong Completely ionized in solution, !.e. the solution wi!! contain a high ·concentration of hydrogen ions, e.g. hydrochloric acid sulphuric acid nitric acid

we k

Partially ionized In solution,

l ...e. some of the .. molecules .remain un-Ionized In the solution e.g. ethanoic acid citric acid [in citrus fruits]

Similar-ly;_ if an alkali completely ionizes on dissolving in water, a ..;.tJwng

alkatl

is produced;

e.g. sodium hydroxide, potassium .. hydroxide, calcium hydroxide. If an alkali does not. complet.ely ionize in· water, a is formed;

e.g·.

·ammonium hydroxide (aqueous ammonia).

we.a.k.

~

(Dr. Falhy Abdel Galil)

-72~

Chemlstiy IGCSE

nre pH scale The strength of an acid or an alkali Is shown using a scale of numbers called the pH scale. On this scale :

an acidic solution has a pH number less than 7 an alkalic solution has a pH number greater than 7 a neutral solution has a pH number of exactly 7

a

The pH can be measured by using universal indicator. Unlversallnd!cator Is a mixture of dyes. Uke litmus, it can be used as a solution or as universal Indicator paper; it goes a different colour at different pH value as shown In this diagram: yellow violet blue orange red ...__ / / / /

~r~;n

'

'

-

'

unlversal!ndlcator colours

1

pH numbers

2...___

2

.....

3

5

4

...___

/

e.g. hydro-

o.g. otha-

chlol1c acid

nolc acid

6

7

8

11\

g 10 11 12 13 14

-"""'
MUiral,

'-... weak alkali.

a.g.water

e.g.aq.l.!TliTlOllla

The pH can be measured more accurately using

pH meter.

/

o.g.&Od!um

hydro>:ida

Salts A salt is a compound made from ari acid when a metal takes the place of the hydrogen in the acid

The salt made depends on the acid : • Hydrochloric acid gives a chloride • Nitric acid gives a nitrate • Sulphuric acid gives a sulphate " Ethanoic acid gives ethanoate.

Soluble and insoluble salts Some salts dtssolve·ln water easily. They are said to be soluble. Other salts do not dtssolve at all. They are said to be Insoluble.

Soluhle

Insoluble

All sodium, potassium, and ammonium salts

All nitrates

except

Sliver and lead chloride

Chlorides •••

except

Calcium, barium and

Sulphates ...

lead sulphate

Sodluin, potassium, and ammonium carbonates •••

But all other carbonates are Insoluble

Chemistry I GCSE


- 73-

Making Soluble Salts 1. A metal, a base or a carbonate can be added to a dilute acid. The

solution formed is then evaporated.

1. . 2.

Excess zinc is added to dilute sulphuric acid in a beaker until the reaction stops fizzing and some zinc is left • The mixture is filtered, What

wil~

be left in the filter paper 7

....................~.····~······································'"···· 3.

The filtrate, zinc sulphate solution, is evaporated in an evaporating basin to crystallizing point.

4.

Allow the solution to cool, crystals of zinc sulphate are formed.

5.

Separate the crystals by filtration and dry them between filter papers (or in a warm oven).

dilute sulphuric- -111/ acid "-=Cd=_,

'

.

~zinc sulphate solution

/·,zinc sulphate /

crystals of

, solution

~~2~;;;----e:Vaporating

'i

basin

zi:!:·

Zinc sulphate-. could also have been made using· zinc carbonate instead . of zinc. The ·sam>;! method and apparatus would. be use<;!, but the gas given off would be carbon dioxide and not hydrogen.

Similarly, zinc oxide could have been used instead of zinc. No gas .would be given off and warming is necessary,

- 74 -

Chemistry IGCSE

2.

(Dr. Fathy Abde! Cali!)

.Making sal!s from acids and alkalis [the titration method] Making sodium nitrate NaN0 HN0 (aq) 3

+

N.a OH (aq)

3

-->

+

d.Uu:te. n.U!Uc. Cl.c).d - - - p.{.pe.tie.

<.ocU.wn /--'---\/ hyd.JW x.J..de. &oWtion

bwr.e.tie.

'-----"Z.

phena.tph:dut.te..&!

<.odW.m rU..i::Jr.JLt e.

<.olu.:Uan

Cl.ci.d.

~

l

ph. ph. j w,;t

c.hCI.ng e.6 p{.nk :to c.o.tou.!rl.e.o<>

l.

A burette is filled to the zero mark with dilute nitric acid.

2.

25 cm 3 of dilute sodium hydroxide is put into a conical flask with a pipette.

3.

3 drops of suitable indicator such as phenolphthalein (ph.ph.) are put into the alkali. What. colour will it turn Z..•.•••••••..•••••••.•.•..•••••••.•••

4.

Acid is run from the burette into the alkali. When the indicator just changes colour (from pink to colourless), the solution is' neutral.

When me:thyi. 01r.a.ng e. (M. 0. ) .U 6Jtam yellow to red •

u.¢ eel C1.6

i.ncU.c.CI.:taJt, :the. c.a.towr. c.hCI.ng e.c,

5. The experiment is now repeated, using the same volume of alkali and the same volume of acid, that has been added, but without indicator. 6. Finally, the salt solution is evaporated to the crystallising point, allowed to cool

- 75 -

Chemistry IGCSE


Making insoluble salts

Salts which do not dissolve in water have to be made by the process ofprecipitation. Precipitation is the formation of it solid when two solutions )>

are mixed together.

Making the insoluble salt lead sulphate [pb SO.] 1 soluble lead salt+soluble sulphate sodiurTI sulphate

scilution Je3d nitrate solution

The two solutions are mixed together. An insoluble precipitate of lead sulphate is formed.

sodium

nitrate solution - - - I t precipitate of lead sulphate···-----.;:;_,_:_"'-'-~'-'

General reaction:

soluble salt

Word

lead· ••.. + .. .-"sodium . ••• , ul h rntrate •·•· ····s p ate

equation:

+

soluble salt

-+

-+

insoluble . + salt

soluble salt

lead sulphate

sodium nitrate

+

Symbol equation: Pb(N0 3 ),(aq) + Na 2 S0 4 (aq)-+ PbSO,(s)

+ 2NaN0 3 (aq)

i (aq) means in aqueous solution (aq)

(aq)

+

(s) means an insoluble solid -+

(s)

+

(aq)

These state symbols show that a precipitation reaction has happened. 2

lead sulphate is filtered off arid washed with distilled water and then allowed to dry.

}>

Making the insoluble salt silver chloride [AgClj AgN03 (aq)

ionic equation:

Ag+

+

NaCI (aq)

-7

AgCI (s)

+

cr

-7

AgCI

. .· . ~

+

NaN03 (aq)

Chemistry !GCSE


- 76 -

Water of cryst:z!lisation Some salts contain water molecules in their crystal lattice. These salts which contain water of crystallization are called hydrated salt. Here are some exampl~s of hydrated salts :

Name

EalUE~

Magnesium sulphate

HgS0 4 ·7 H2o CoClz • 6 H20

-

c~so~:s-H;o

carr~~
Cobalt chloride

_____ _

If the water is removed by heatipg, the crystals often change in appearance and the anhydrous salt is. fo-rmed;·' Heating copper( 11) sulphate crystals (hydrated)

1 /~' I r: ,..

--

.1/1' - - - 7.----

3.

S~eam ~ g~ven

2. Canden.;atian a.t

a6 copper(II)sulphate crystals (hydrated},_~~::_-

a66 ~he ~ap

~e ~ube

I. Ca.tawr. c.ha.ng wiU:te

de.hydnttion CuS0 • 5 H 0(s) 4

+

2

hydrated copper( II) sulphate (blue]

hydnttion

anhydrous copper( II) sulphate [white]

Wh_-n

these. blue- crystals are heated, steam is given off and the· crystals change to a white powder called anhydrous copper(II)sulphate. If water is added to the anhydrous powder, it gets very hot and changes back into blue copper(II)sulphate (hydrated}. This is a reversible. reaction. Anhydrous copper(II)sulphate can be used in this way to test for water. Test for Water [chemical testJ

Add anhydrous .copper(II)sulphate, the colour changes from white into blue.

Physical test for water Pure water boils at 1oooc and freezes at

ooc

Heating cobalt( I I) chloride crystals (hydrated) CoC! • 6 H 0(s) 2 ~k.

2

.-···

Chemistry lGCSE

{Dr. Fathy Abdel Galli)

- 77

TYPES OF OXIDES 1.

~he

Acidic oxides are usually

oxides of non-metals·

Ac.l.d.ic. oxide.

. co 2 so 2

(arbon ·dioxide Sulphur .d__ioxide

-

Sulphur ·trioxide

S0

Phosphorus(III) oxide

P203 NQ 2 Si0 2

Nitrogen

qxide.

I~:>

dioxid~

Silicon dioxide

3

~e4-l:>otuble

yes

pH 6

yes

p~ l

yes

pH l

yes

pH l

?

-··..PH l .

yes no

1.)

Acidic oxides dissolve in water to form acidic solutions.

2.)

Acidic oxides react with bases to form salts and water.

(vu~rbon -y co

1

dioxide + Calcium hydroxide

-7

.· . ·.·.··.

Calcium carbonate

+ Ca(OH) 2 (aq)

(g)

(lime water)

Explain why carbon dioxide turns lime water milky 7

o.§.

... .b. ~s-AJ..t$..~.. t~ .LJ'n.S. ..+~ . ~~.Ql~te. ~r't~.p.p. h,.c.a£ 2.

Basic oxides· are the oxides of metals

I..s a~~ ~~ Joluble f Potassium oxide

K 0 2

Sodium oxide

Na

o

yes

pH 14

yes

pH 14 pH. 12

Calcium oxide

2 CaO

Magnesium oxid e

MgO

no

Copper(II) oxide

CuO

no

Iron(III) oxide

Fe

1.)

o

nci

2 3

They react with acids to form salt and water

CuO + .H2S04 2.)

yes

-) C)lS0 4

+ H20

If they dissolve in wat er they form Na 20(s)

+

H20(l)

)

alkalin~·

2 NaOH (aq)

solutions •

Chemistry IGCSE


- 78 -

;.· ·

3.

Amphoteric oxides are the oxides of certain me tals .

e.e.

aluminium, zinc

7

\e.c:J

They have the properties o f both acidic and basic oxides, i.e. they react vith both_alkalis and acids to form salts and .'Wa ter,·

Ampho.tvr.J..c. oudu

'a.Jte.

.<.n.oo.tub.f.e .<.n. u.u.t.Vt.

Aluminium oxide + hydrochloric acid

+

Aluminium chloride + water

6HCI

2 AJCh

Aluminium oxide + Sodium hydroxide 4.

Sodium aluminate

+ water

Neutral oxid e s are the oxides. which do not dissolve in acids or

:.:·:

alkalis. e.g. NO_, CO ,

basic. oxides (oxides of metals)

acidic oxides (oxides of-non-metals)

alka~~--r-~ salt+ water 'r"-

acid

or alkali

amphoteric oxides (Ah0 3 and ZnO)

Question: Complete the table that shows the reaction, if any, of the oxides with acid and alkali. Indicate a reaction with "R" and no reaction with "NR".

oxide

type of oxide·

magne·sium oxide

basic

aluminium oxide

amphoteric

silicon(IV) oxide

acidic

reaction with acid

reaction with alkali

··.·

-(3)

Chemistry IGCSE


- 79 -

·:-·

Identification of Ions Test for Anions Anion

Test·

Carbonate

Add dilute acid

ceo;

2

Result -

Effervescence, co

produced 2 (turns limewater milky).

(e • g. dil. hydro-

J

chloric acid)

Chloride (CI-) [In sol.ut!on]

Acidify, then ·-add . aq. silver nitrate

White ppt.·.. of .1\gCl

Acidify, then add

White ppt. of PbCl

Ag+ + Cl- -+

AgCl 2

aq. lead nitrate

Iodide ( I )

Acidify, then add

Yellow ppt, of Agi

[In solution]

aq. silver nitrate

(or Pbi ) 2

(or lead nitrate) .

Sulphate (S0

2-

4

)

[In solution]

Acidify, then add

White ppt. of Baso

aq. barium chloride

Ba 2+ + S0 2"4

(or barium nitrate)

-+

4

naso4

..

Nitrate (NO;) Tin solution]

Add
Ammonia produced

aluminium powder),

paper blue).

(t;urns damp i:ed litmus

warm· carefully

)> Complete the following table to differentiate between hydrochloric acid, sulphuric acid

and nitric acid Test Add aq. silver hitrate . Add aq. barium chloride

HCI (aq)

H 2S04 (aq)

HN03 (aq)

Chemistry IGCSE


- 80 -

~:.

Test for Cations

{

r

Result ofadding aqueous ammonia

Result of adding aq: sodium hydroxide

'

Cation

. Copper (II) [ Cu

Blue ppt. of Cu(OH) 2 , insoluble in excess

]

'

[Fe 2 +J

'

Fe(OH)

2

excess

insoluble in

{tuAno

--

. - - .. ------ - . -

in excess

-~ed-b~own

on the .OWt.6a.c.e due ;to axJ..da.tio n) Iron (Ill)

[Fe 3+]

Red-brown ppt. insoluble

Red-brown ppt. of Fe(OH) 3 insoluble in excess Fe3+ + 3 OH ---+ Fe(OHh

in excess

~

2 Zinc [ Zn +J

•

. ----- - -- -

3 Alumlnlum [A! +]

'

White ppt. of Zn(OH) 2 ' I' ' I soluble in excess {g.iv.Wg

\ a. c.o.towU'.e.o.o .o o.e.u.ti.o n J ... - - - -----_....

--

-

/

---- of

White ppt.

, t I

-Al(OH) 3

I I

1

/

•

'

\

a. c.o.towU'.e.o.o 6otut£on)

1

'

- ---

-

- -

-

- - -- -White ppt.

- -

-

soluble ' \

I

in excess {g-iving I I ( a. c.a.to u4e.e.o.o .o o.e.u..ti.o n) , ' ... / - - - - -

-

-

White ppt. insoluble in

soluble in excess {g-iv-ing,'

I

excess

-- /

[A.t{OHJ 3 and Zn{OHJ 2 ~e

0111photeM.c. hyd.Ao xJ..de.o l

Calcium [ ca2+]

White ppt. of Ca(OH)

2

No ppt.

insoluble in excess

Ammonium [NH:]

Ammonia is produced on warming with uq. sodiu1u hydroxide

-'

excess~

Dirty-green. ppt ,__ inso.luble ·

Dirty-ereen ppt. of

'

~

' giving dark blue solution ' .

Cu2+ + 20H- -7 Cu(OH)z

Iron ( II l

-

--- ---. . :Blue ppt. soluble in ~

2+

...

~

•..

~

.

- 81 -

Chemistry I GCSE

Topic 8.


Metals and Reactivity Series

Physical Properties of Metals _ 1,

Metals are shiny (lustrous) Yhen freshly cut and polished.

2.

Hetals conduct electricity because the electrons can move about inside the structure, They have usually high densities

3,

because the atoms are packed closely together in a giant structure,

They usually have high melt'ing

4.

points and boiling points.

5.

They are

malt~bte

(can be ham-

mered and rolled into shape) and du.ctU.e (can be stretched into wira). This is because when force is applied to metals, the

la~Jars

of a toms can slide.

over each other. 6.

Hetals are good conductor.s of heat •

............................... . . . . . . . . . .. . . .. . ..... .. ... ... . . . .." ......................................... . ~--y~·············~·························

Alloys 1.

An alloy is usually a mixture of two or more metals or of metal and a non-metal.

2.

Alloys are formed by mixing molten metals together and allowing them to cool.

Ex.ampleo on rllo y~o . : B4aoo ~ an aLLoy on eopp~ and ~e. &.onze ~ an aLLoy on c.opp~ and .tin. S.teeL ~ an aLLoy o6 .UC.on and c.oJr.bon;

Chemistry I GCSE

(Dr. Fathy M. Abdel Galil

- 8 2-

Alloying often results in metal which is

stronger. than any one

of its eomponents. For example, b~L>, which is an alloy of copper and zinc is stronger and harder than the pure metals. The following is a diagram showing the structure of an a.lloy ·.·

0

•

me,.ta.£ a.to m6 o;thvr. metal dom6

Uses of Metals related to their Properties

Aluminium high electrieal

conducllimy

yens;cy (ov/

overhead C
aircraft (aeroplanes) carengihes

Ov e.Jthea.d a1.wrU.iU.wn el.ec..tlr)_c.al. c.a.b.te6 ha.ve a. L>.tee1. co11.e.

window frames

cans Food containers

aluminium

The L>.teel. c.o11.e L>.t11.eng.then6 ;the c.a.b.f..e.

g£EE0_.: I.t L6 u.oed e.g. : 1. In· el.ec:tiUc w.Ute6 bec.a.u.oe c.oppeJr. L6 du.c.t.Ue, a: good .c.andu.c.tolt o6 el.ec;tJUcA.:ty, on .tow Jtea.di..vU!f a:nd haL> a. IU.gh m.p. 2. In c.oo!U.ng u;tert.6ili beCJJ.LL6e c.oppvr. L6 a. good c.ondu.c.tolt o6 hea-t. 3.

Making brass which is an alloy of copper and zinc

- 83 -

Chemistry I GCSE


Reactivity series

K

.l

::;

extracted by electrolysis

a..tta.c.k Lll:lteJL --r hy d!to :Ude. +

Hz Jtea.c.t.

Mg

C-+

A.t

Zn

.....-.._,. ->a..U + Hz

a.tta.ck ;,.te.a.m ---'7 o:Ude +

..

Hz

Fe

o:Udu a.Jte. Jte.duc ed w.Uh c.Mbo rt

w.Uh

d.Uu..te. a.cJ.do

Pb (H)

Cu

Ag Au Action of· Water on Metals

a)

Potassium, Sodium, Calcium

--------------------------

Reactive Metal + Water ----7 Metal Hydroxide + Hydrogen

Potassium and sodium react violently

+----+-Hydrogen

· with cold water, ( see page-49 J Calc·ium reacts raadily but not violently

Water

with cold water to form hydrogen and calcium hydroxide solution, the alkali -U.me wct.te.Jt.

Calcium reacts steadily wi!h walet.

calcium + water ----7 calcium hydroxide + hydrogen

Ca (s) +2H20 Q) --'-+

Ca(O~

(aq)

+ H2 (g)

St~te two observations you could make when a small piece_ ofcalciu~ Is added to cold' water. Observation 1 ·-···-····-·····--··················--···--.--........... - ................- ................................................ .. Observation 2 ·-·-·-·--------................................................................................................................... [2]

- 84-

Chemistry IGCSE


Magnesium

Reacts very slowly with cold water to form hydrogen and magnesium hydroxide.·

rI

When heated in steam, magnesium turns to a white powder (magnesium. oxide)

Heal

Magnesium

+ _Steam

Magnesium oxide

+

Hydrogen

Mg(s)

+

• • • • • • • • • • . . • ( s)

+

• • • • • • (g)

--> H O(g) ·-> 2

Hydrogen burn1ng

React only with steam to form hydrogen and the oxide.

Reaction with Dilute Acids Metals above hydrogen in the series react with dilute acids and hydrogen is produced. This is a displacement reaction in which the metal displaced the hydrogen of_ the acid.

ri nc

+

Zn(s) + zinc

+

+ hydrogen

hydrochloric add ....-...;:. rinc chlor-ide

+

- - 7 .......... ..

sulphuric acid

--->- rlnc sulphate

+

hydrogen

Zn(s) +

)>

)>

)>

It is too dangerous to react the very reactive metals potassium and sodium with acids and would caitse aplosion. Aluminium seems to be unreactive due to the protective layer of Al203 . Remember that Cu, Ag and Au do not react with ·,vater, steam and dilute acids.

-(Dr. Fathy-Abdel ·calif)

- 85-

Cherr:lstry IGCSE

Making hydrogen in laboratory:

Hydrogen is _prepared in laboratory by reacting zinc or magnesium with -dilute hydrochloric acid or sulphuric acid. acid

hydrogen

water

zinc

Reaction of Metal Oxides with Carbon Carbon, on heating, will reduce the oxides of zinc and of metals below it in the reactivity series.

iron (Ill) oxide _+ ··Fe 0 2 3

+

carbon

.; c

---~

iron

~··Fe_

+ carbon dioxide + .. co

2

Competition for Oxygen : [Reduction of metal oxides by a more reactive_ metal]

A metal oxide can be reduced tr:_ ·.:he metal by heating it ·with another metal which is above it ir, <.:i)e reactivity series, i.e. more reactive.

iron( Ill) oxide

+ aluminium-+ Iron +2 AI

i.-e. Aluminium is more

r~active

-------7 2 Fe

+ aluminium oxide + A! 2 0 3

metal than iron.

It combines with oxygen more strongly, so it can reduce iron oxide.

:;.·:

:

.

- 86 -

Chemistry !GCSE

(Dr. Fathy Abdel Gali!)

:.··

Displacement Reactions

Any metal will displace one lower in che reactivity series from aqueous solutions containing its ions. If a piece of iron is placed in copper(II) sulphate solution (blue), a reddish-brown deposit of copper forms on the"iron and the blue colour of ·che solution fades. This is a Jr.edox reaction in which iron atoms are oxidised by loosing 2+ 2+ two electrons and going into solution as Fe ions; Cu ions are reduced by gaining tWO electrons and forming a solid deposit of Cu atoms.

Fe(s)

+

CuS0 (aq) ----7 FeS0 (aq) 4 4

ionic equation: Fe ( s)

+

Cu

2+

(aq)

----7 Fe

2+

(aq)

+

Cu(s)

+

Cu(s)

A metal cannot displace another above it in the reactivity series. Thus, if a piece of Cu was placed in iron(II) sulphate solution, no reaction occurs.

Similarly, copper does not displace magnesium. from magnesium sulphate solution, but copper displaces silver from silver nitrate solution (silver is below copper in the series).

Finding the order of reactivity of metals : Ey placing a metal in an aqueous salt solution of the other metal and observing if displacement takes place or not.

aqueous solution

Iron·

zinc

copper

sliver

zinc sulphate Iron (II) sulphate

__,_______

-p~~~~ry/.07/,ry~--------4

copper( II) sulphate silver nitrate

V

=

=

r.eaction occurred

no reaction

Arrange the above elements in order of their reactivity (the most reactive metal first) l.

.. .

...... ..

2.

3.

. ......... .

4.


- 87 -

Chemistry IGCSE

.·.:

Things to remember about the reactivity series : 1. The tnore reactive the metal, the more it 'likes' to form compounds.

S~ only copper, silver and gold. are ever found as elements, i.e.

uncombined in the-earth's crust The other metals are always found as compounds : oxides, carbonates, sulphides and chlorides. 2. The more reactive the metal, the more stable its cr.'mpounds. A stable compound is difficult to break down or decompose. Compare what happens when these hydroxides and nitrates are heated. Action of Heat on Metal Hydroxides and Metal Nitrates /Metal

II

Hydroxide

Nitrate

II

do not decompose K

KOH

Na

NaOH

Ca Mg AI Zn Fe

heat

heat heat

)

Ca(OHh

heat .

I no reactwn

ZKN03(s)

I

1 metal nitrite+ oxygen

heat I ZKN02(s) + 02(g)

i no reaction

metal oxide + water heat ) CaO+H20

decomposition gets easier down the series

heat

metal oxide,' nitrogen dioxide (brown gas),+ oxygen heat 2Ca(N03)2 I 2Ca0 + 4N0 2 + 0 2 decomposition ·gets easier down the seri ~s )

Pb

Cu

Cu(OH)2 blue

heat

CuO+ H2 0 black

)

2Cu(N03)2 blue

heat ' 2Cu0+4N0 2 + 02 black

The breakdown of the compound by action of heat is called thermal decomposition.

Extraction of Metals: Metal

Ore

Compound

Formula

Method of Extraction

A!

Bauxite

Aluminium oxide

Al203

Electrolysis of molten Al203

Fe

Haematite

Iron(III)oxide

Fe203

Reduction of the metal oxide by coke (carbon) in a blast furnace

.

Zn

Zinc blende

Zinc sulphide

ZnS

Ore: minenil found in the earth's crust from which metal is extracted

Chemistry I GCSE

(Dr. Fathy Abdel Ga!ll)

- 88·-

Extraction of Iron iron(III)oxide; fe 2 o ; in 3 large quantities, by reduction in a blast furnace. Iron is extracted from iron ore, haematite;

1.

Iron ore, coke and limestone are added at the top of the blast furnace. A blnst of hot air causes the coke to burn.

2.

carbon

+

oxygen

carb.on dioxide

C(s)

+

o 2 (g)

C0 (g) 2

The carbon dioxide rising up the·furnace reacts with more coke· to form carbon monoxide which reduces the iron oxide to iron.

carbon dioxide

+ +

irori oxide

.;.

carbon C(s)

carbon monoxide 2 CO(g)

----;>->-

carbon monoxide

Iron 2 Fe

+ carbon dioxide

+ 3 Co

2

As iron reaches the lower part of the furnace it melts and runs

to the bottom of the furnace.

3.

The purpmse of limestone is Co remove the

s~ndy

impurities,

mainly silicon(IV) oxide [Si0 ). 2

a)

Limestone is decomposed by heat

calcium carbonate

____,..

calcium oxide CaO

b)

Th~· !1

+ carbon dioxide

+

co . 2

basic oxide, CaO reacts with Si0 , an acidic oxide to form 2

liquid slag which runs down to the· bottom and floats on top

of iron. .. ·

•

calcium oxide·+ silicon dioxide

--,.~)

+

----;>

Ca')

SI0

2

calcium silicate (slag)

CaSJo

3

- 89 Chemistry IGCSE


Cast Iron The iron produced in a blast furnace is .called cast iron. It is brittle and impure [contains about 3 -

4~

carbon]. l1ost cast iron is converted

into steel. Making Steel Oxyg~n

is passed tl:ir.ough the molten .rron [ containing . 3.:4% carbon], where carbon is oxidised into carbon dioxide and pure iron remains. The required amounts of carbon are added.

molten iron containing . imr:>urities

/,

~~-~~~~-1~~-~2£~-~~~~lL-l~~q-~~2~1 contains about 0.25;1; carbon, u·sed for car bodies and machinery.

As the carbon content is increased, the steel becomes stronger and harder. In o.ther words, steel has a range of hardness depending on the

car body

percentage of carbon.

z.

!i~a!!-_£!¥.E2£!!_~~g.!?:f contains about 1% carbon, used for railwey lines and _bridges and building construction

3. e.g.

stainless steel [doe.> no.t IU(h.t}, contains nickel and chromium,

~·.

and is used for cutlery and surgical instruments.

and chemical plants

cutlery

- 90-

Chemistry lGCSE


···.,. Extraction of Zinc Zinc occurs as the sulphide, ·zinc blende; ZnS. l.

The blende is roasted in air to the oxide ':.

zinc sulphide + oxygen (air) ---7 zinc oxide + sulphur dioxide 2 ZnS(s)

2;

----') 2 ZnO(s)

Zinc oxide· is then reduced with carbon (coke) 'in a blast furnace. zinc oxide + carbon - - - 7 zinc 2 ZnO(s)

+ C(s)

+ carbon dio;x:ide

2 Zn(s) +

co 2 (g)

Uses of Zinc l.

~~!~~~!~!~g-~

The metal is used to protect steel objects from rusting; the zinc. coating (galvanising)· corrodes instead of steel.

.2.

..

~~!~~-~E~~~-~ Brass is an alloy of copper (60%) and zinc (40%). ·~

RecyCling Metals All metal'S can be recycled, that is, to melt down used metals and use them again rather thac throw them nway.

R~cycling

makes sense

because :

l.

It saves money and energy for extraction.

2.,

It saves mineral resources since resources of or.es are limited and cannot last forever.

3.

<.:.

It solves the problem of waste disposal. Re.cycling metals stops them causing pollution and spoiling the environment.

Re.cye.U.ng o:the.Jt ma.teJUaLs : G!a..6.6, pa.pe.Jt, cl.o.th a.nd p!.a.olie.6 ca.n a.U be. Jr.e.cyc.f.e.d. Foli. e.xa.mp.C..e.,

o.e.d g!.a.o.6 bo.tte.u can be. meLted dawn :to ma.k.e. neW bo:t:Uu. T!Uo -"a.ve.-0 Jr.e.haUJi_ce.-6 a.nd .oo.tvu paUu.tion pltob.te.m-6.

.,:


- 91 -

Chemistry IGCSE

Rusting The. corrosion of iron and steel is· .called ·IULbWrg ,·

l. ·-2..

Rust is the red-brown flaky nolid which forms ons iron and steel.

3.

Rusting is the. slow oxidation of' iron to for.rt hydrated iron(III) oxide. This is the. chemical name. for rust.

4.

Both

~

nnd

waXe4

are needed for. rusting to occur.

Iron + oxygen + water --;.-hydrated iron(lll) oxide 5.

(rust)

Rusting occurs .rnrticularly quickly in water containing dissolved ionic impurities - such as sea water.

;

);> Suggest what elements rust contains. •oooooo••••~••••.••••••••••~•••.•••
What happens when rust is heated 7

......................................... ······~· . ···········~·· . ,. ........ ·.

Z. _conde.Ma..Uon

Name the solid-left :

Air and water TUBE A

TUBES

Boiled water

Dry air

TUBEC .

TUBED

oil to slop · air dissolving In the water

distilled water

sea water

boiled

nails

heavily rusted

naUs rusted

no

no

rusting

rusting

An e.xperimenc co investigate the conditions needed for roscing.

'

Chemistry IGCSE

-92-

[Dr .. Fathy Abdel · Galil)

Methods of Rust Preven-tion 1.

Iron and.ateel can be protected from rusting_ by preventing air and water from reaching the surface. This can be done by painting, oiling, galvanising or electroplating the iron surface.

2,

s~~6icial p4ote~on

: Block of

magnes~um ~r zinc are attached

to the iron, e.g. ships' hull or underground pipes. The magnesium or zinc (being !!lOre reactive than iron) ar~ oxidised in preference to the iron.

,..

zinc blocks fixed to hull

)> Zinc blocks are attached to the steel legs of oil platforms (oil rigs)

!•

.· -·

sea

(i.) Explain why the zinc blocks prote.ct the steel legs from rusting. [2] (ii) From the reactivity series name ariother metal that could be used for the blocks in place of zinc: [1]


-93-

Chemistry IGCSE Topic 9. CHEMICAL CHANGES ENERGETICS OF A REACTION

All chemical reactions involve an energy change (ll. H). This energy is in the form of heat. An exothermic reaction is a reaction, which releases energy to the surrounding, i.e. heat is given out (the reaction mixture becomes hot). An endothermic reaction is a reaction, which absorbs energy from the surrounding, i.e. heat is taken in (the reaction mixture becomes cold ). exothermic reaction:

endothermic reaction:

HEAT

/ t

HEAT

HEAT

· w·here does the energy change (ll. H) come ..from ? :· In chemical reactions bonds are broken and new bonds are formed.

Breaking bonds requires energy. It is endothermic. Making new bonds gives out energy. It is exothermic. If the energy given out is greater than the energy taken in, the reaction will be exothermic.

>- the following is equation for the combustion of methane (natural gas) CH 4 H

I I

+

2 02

o=o

H-C-H H

.->-

and 2 x 0=0

o=c=o

o=o

We need to break these bonds:

4xC-H

+

We need to make these bonds: 2 X C=O . . . .

and 4 x H-0

- - -

Explain using the idea of bonds forming and breaking, why the above reaction is exothermic .........................·......................................... ·.· ...... -··.--·-........................................................................................................

[Dr. Fathy Abdel Galil)

-94-

Chemistry IGCSE

Examples (or exothermic reactions: '

1. All neutralisation reactions are exothermic. When dilute hydrochloric acid reacts with sodium hydroxide solution, a neutalisation reaction happens. hydrochloric acid HCl(aq)

+ sodium hydroxide-+ sodium chloride +

water

+

HiO(l)

NaOH(aqj

--+

NaCl(aq)

+

fmal temperature= 34°C

initial temperature = 21 °C

temperature rises by (34.,.. 21) = 13°C

> Why a polystyrene (plastic cup) is used instead of a beaker? .................................................... )>

Predict what the temperature of the reaction mixture in the experiment would be after 1 hour. Explain your answer. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . .

2. All displacement reactions are exothermic:

7

MgS04 (aq) + H 2 (g)

7

ZnS04 (aq)

+ H 2 (g)

By measuring the rise in temperature we can find mit the order of reactivity of metals.

Chemistry IGCSE


- 95-

Examples (or endothermic reactions: 2 NO(g]

1.

This means that energy is

2.

needed for the reaction to take place

Thermal decomposition.. Melting of ice and evaporation of water.

3.

PRODUCTION OF ENERGY ,·,>1

Burning Fuels Fuels release heat energy when they burn in air or oxygen.

~

burning reactions are exothermic. Natural gas

i~

largely methane,. When it burns,

methane + oxygen CH

4

+

z 02.

~carbon

------1-

diox1de + water

J ) )

co 2

he.a..t .{;, given 'ocU

Ethanol (used in cars in Brazil). When i t burns,

ethanol

+ oxygen --7 carbon dioxide + water +30

2

--72C0 . 2

+3H 0 2

) he.a..t .{;, J given aU-t )

What is needed for a fire ?

Hydrogen as a Fuel Hydrogen is a possible energy source of the future. Hydrogen can be used as a fuel for cars. It causes no pollution because the only product of combustion is water.

Nuclear Energy Uranium- 235 as a source of energy [see page !9].

-.----~----

~-

,_

···- ..

..

Chemistry IGCSE

-96-


Comparing the amount of energy produced by the burning of different liquid fuels: The apparatus below could be used. The same mass of each fuel is burnt in turn. The initial and final temperature of the same v-;iume of water is recorded

metal

container

f--

thermometer

clam p :.·

water

i) wick

draught shield

j

0:,

t

:~:~· ......"r.

r----

-----

spi rit bu mer

l iquid

.:.-

fuel

Questions: Suggest how you could work out which fuel produced more energy .

. ..

. . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

What are the sources of errors in the above experiment?

............................................ ; ................ _- ............ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - ... ' .

I.

-97-

Chemistry IGCSE


-.-.·

Electricity from Chemical Reactions : Cell :

a device to produce electrical energy from a chemical reaction

This is the reverse of what happens during electrolysis, where chemical reactions are brought about by the use of electrical energy. Electrolysis (endothermic)

Electrical energy

----------__:~

t

Cell (exothermic)

Chemical reaction

Simple cells Two metals

that are far apart from one another in the reactivity

series are placed in an electrolyte. The more reactive metal becomes the negative pole from which electrons flow.

The amount of electricity produced (voltage) depends on the position of the metals in the reactivity series, The rule is : The further apart the metals are in the reactivity series the more electricity is produced.

voltmeter

Mg AI

copper - - - l l l

Zn Fe Pb H Cu Ag

Au dilute acid

:>

The voltage of an -ironicoppercell is about 0.8 volis. Predict whether the voltage of a zinc/copper cell would be less; the s·ame ar bigger. Explain your an?Wer. ·

.,-.,-.-.-- "''"'"~'··-.-.··.----,-----:-..-.-;-

··--·

-- -- ....

Chemistry !GCSE

(Or. Fathy Abdel Cali!)

- 98-

The simple cell can be used to compare the reactivity of two metals l.

The more reactive metal is the one which loses electrons and i~e.

passes as ions in the solution,

2.

becomes thinner;

The direction of flow of e- is from the more reactive metal to the less reactive one.

Question : :::::========= How could the simple cell shown below be used to find out if zinc is more reactive than cadmium ?

·-

voltmeter

zinc

cadmium electrode

electrod.:;

-=1--- dilute sulphuric acid

............................................................................... •

•

•

..

•

0

•

0

.......................................

0

0

•

0

....................

0

..............

.

The Zinc Carbon Dry Cells: [Batteries] Batteries are convenient source of energy because they are portable and small, and are used in toys, radios, torches and many other things.

-99-

Chemistry IGCSE

(Dr. Fathy Abdel Cali!) ·.·.·

Topic 10.

CHEMICAL REACTIONS

-Rate of Reaction The rate l.

of a chemical reaction can be increased by :

l/,_a_king the size of reacting par·ticles smaller, i.e. increasing the surface area of the reactants.

2.

Increasing the. concentration.

j·:

Iricreaaing the temperature..

4.

Adding a suitable catalyst.

5.

Light (applied to a few re.actions).

Plotting Graphs of Reaction Rates FoUow.i.ng

IUJ.;te

o6 1r.eac.tion by mea..&UJU.ng ga..& vo.twne :

Take for example the reaction between magnesium and excess dilute hydrochloric acid :

magnesium + hydrochloric acid--+ magnesium chloride + Mg(s)

+

2 HCI(aq)

Measurements made are

---+

MgCI (aq) 2

+

gas volume and time.

__,.. the plunger can move out

gas s.yringe

stop clock

The volume of gas in the ayrin•;e is noted at intervals, for exal'lple at the end of each half-minute, How would you know when the reaction is complete ?

...........................................................................

- 100-

Chemistry I GCSE


Here are some typical results: Time/minutes

0

l

1

ll

2

2!

3

3!

4

4!

5

5!

6

6!

Volume of hydrogen/em'

0

8

14

20

25

29

33

36

38

39

40

40

4D

40

These results can be plotted on a graph, as shown

'.

Shape a 6 .the GJtir.ph I.

The 6a..o.tvr. .the II.e.ac..Uon,

curve llal, raacllon over

.the. <>.teepvr. .the. cWLve.

curve· loss sleep, reaction slower

, 2.

When .the II.e.a.mon ;_;, ovvr., .the cwr.ve goe.<> u.f.a..t.

curve steepesl, teacllon fastest

The reaction is which a gas given off, e.g. an acid and Ciirbonate, the rate of reaction can be followed up by measuring the decrease in mass of reactants .with time. i.e. the balance reading decrease as the reaction takes place.

/

fast

.

add

, ..

ca.f.uwn

cMbona..te. slow

time (s)

Chemistry IGCSE

Investigating the Rate


- !Ol -

of a Reaction

Effect of particle size This effect can be examined by reacting equal masses of calcium carbonate with different particle sizes (e.g. chalk powder and marble chips) with equal volumes of the same hydrochloric acid.

The volume

~f.

th; _produced

co 2

can be measured using

a_~as

syringe

and is plotted against time.

A

=

U
B

powde;t

~

U
chip~

gas syringe

2 3 Time/minutes

Curve A is steeper than curve B; this shows immediately that the reaction is faster for the powder calcium carbonate. The result shows :

The rate of a reaction increases when the surface area of a solid reactant is Increased.

The danger of explosive combustion with fine powders and gases [e.g. flour mills and mines] :

F.toW!. ht a. ba.g -L6 di£ 6-{.c.uU :to bW!.l1.. A m.ix.twr.e. o6 {toW!.-duo:t a.rid a.Lt ma.y e.xp.tode. i6 ~paJtk.e.d. Why 1A th-U ? '

..•.••.••••.. • ..... • • • • • • • • • • • • • • • • · • • • • • • • • · • · • • • • •

................................................................... .

4

5

Chemistry I GCSE


- 102-

,.'. Effect of concentration A reaction can be made to go faster by increasing the concentration of a reactant.

T/U.6 if, 6ec.aJ.L6e -<.ncJtl211ll-<.ng .the c.onc.en.tM.:t<.on on .the Jtea.cta.n:U -<-ncJteJUV> the numbeJT. on c.oUJ.l..(.otW between pCl.ll.ti.c.tec, and, .theJT.enoJte, .(.ncJteMe6 .the tu:Lte 0 n JU!.ac.tio n. T/U.6 a.tbo exp.taJ.iU Whlj .the gJtea.;tec,t Jta.te on Jtea.c.tion if, u.Wa.U.lj CU. Man cu. the uacta.n:U Me nU.xed,- i.e. thelj Me both at thUJT._ JU-g hut c.one:ert.Vc.a.tio r«>. M the Jtea.c.tio n pJr.oc.eed6 the c.o nc.en.tM.:t<.o IU an the h.ea.c.t-<.ng .o u.b.ota.nc.u decJtea..o e and the tu:Lte o6 Jtea.c.tio n decJteJU e6 . ( i)

(ii)

The effect of "concentration can be shown by doing several experiments using equal masses of magnesium ribbon and hydrochloric acid of different concentrations. The effect of concentration can be also shown by investigating the rate of the reaction between sodium thiosulphate and hydrochloric acid :

add dilute acid and start timing

·view from above the flask

sodium thiosulphate solution

·....

cross drawn --f._;~_.--, . on paper '·-··-·· ·············-· .:

·...........

'

~

........'··.

At first the cross could be seen clearly. When the solution became cloudy and the cross was no longer visible, the clock was stopped and the time recorded.

The c.tou.fuec,.o

if, due

to the

pJr.eup~on

on .wlphu.Jr., (yellow) •

A series of experiments can be carried out using a solution of sodium thiosulphate and hydrochloric acid of different concentration. The results show that the more concentrated the solution, the faster the rate of reaction.

\'

t=.

Chemistry IGCSE

- 103-

(D.r. Fathy Abdel Galli)

Effect of catalyst A catalyst is a substance vhich speeds up the reaction but remaitls .chemically unchanged at the end of the reaction. Enzymes are biological catalysts. [protein innnturc

I

At room temperature, hydrogen peroxide decomposes very slowly·.

If a cacalyst called manganese(IV) oxide is added, decomposition takes place very rapidly. If the manganese (IV) oxid-e J.s ;filtered off at the end of the reaction,

washed, dried, and reweighed, it will be found that its miss· has not changed. ifuy 1

9tw••••••••••••••••;•••••••••~'••••OOOOOOOPO•••••••'••••oooo••••t

gas syringe with catalyst

without catalyst hydrogen peroxide

lr---solution manganese (b.Utck )

time

(IV) oxide

nuestion :

daa=•-=•"a.::

The speed of decomposition of hydrogen peroxide is investigated using different catalysts. State the precautions which should be taken to make this a fair test :

........ ........................................................................ . ... ... .. .. ..... .......... . ... .... . ... ..... " ........... ' .. ' ............... . ...-

" "

........................................................................ , ................. . .. " ................................................................................... .

Chemistry I GCSE

Dr. Fathy Al:""'el Cali!)

- 104-

Effect of temperature : A reaction goes faster when the temperature is raised. When the temperature increases by

1o•c,-

the rate approximately doubles.

Explaining the factors affecting reaction rates: The collision theory The reason for an increase in the rate of a chemical reaction can be explained by the collision theory. In order for particles to react,.they must collide, and they must have sufficient energy to react. 92;~S!£~.,:.

··-

,

Uu. .the .Ldea. o6 .the c.o.U.U.Lon :theoJty :to ex.p.&Un .the e06 ec.t; o6 <>uJL6a.c.e Mea.,· c.onc.ell-tlt.a.-Uon, a.nd :tempeJta.:tu!te on .the ;w;te o6 !tea.c.tion .•••.•. .• 0

0

0

I

0

o 0

o 0

o o 0 0

o o o o o o •

~ 0

o 0

o o o o o 0 o o o o o o o 0 o 0 o o o

o o o o

o •

0

o o o o o o o 0

0

o 0 o o o o

.. o 0

o

. Effect of pressure : (for gaseous reactions only) Increasing the pressure makes the ··mo-lecules of the gases close to each other and the

fre~uency

of.

collis~Qn

increases and the· reaction

_goes faster.

Investigating the effect of light ~-

The <.peed<. of, <.ome !tea.c.tion<> lnc.!tea.<. ed by expo<. uJLe :to .Ugh:t. When a silver salt is exposed containing white

to light, silver is formed. The

;Uver chlorid~.t

.suspension.

figure shows an _experiment with silver chloride. Light has the

Exposed to light REMOVE

FOil

V

effect of decomposition of silver chloride. 2 AgCI

>2

Ag + CI

2

Such reactions which are affected by light are called photochemical reactions.

TUBE A: still while when foil removed

TUBES: darkens

Tne effecc of light" on che decomposicion of Silver chloride.

Chemistry IGCSE

-105-


Photography The deco"mposition of silver bromide· (AgBr) to silver is the basis of photography. The film is covered with silver bromide. When light shines on the film, silver is formea. This is the black part of the negative. The unexposed silver bromide stays white.

>

2 AgBr

+

2 Ag

white

Br

2

black

unexposed

Jt

photographic film

grey

black

remains white

Photosynthesis: Photo.synthesis is one of the most important reactions involving light. Chlorophyll is the catalyst. The; ,green chlorophyll in the leaves absorbs light energy from the. sun and uses it to make(synthesise) sugars from. carbon.dioxide and water..

sunlight carbon dioxide + water

glucose + oxygen chlorophyll

i.e. the process of photosynthesis is endothermic and the energy required comes from the sun Respiration: Respiration is the reverse of photosynthesis and is an exothermic process. The process of respiration can be represented as: ..

glucose + oxygen --7

carbon dioxide

+ water +

energy

(Dr. Fa thy Abdel Gal ill

- 106-

Chemistry l GCSE

Reversible Reactions A Jtevvu.i.b.t~ Jtea.c:Uon, is one which can proc~ed in either direction depending on the conditions under which it is carried out. A

B

+

reactants

£o/W!a)td Jte.a.c:Uon ,

c

ba.dwxvr.d Jtea.c:Uo n

+

D

products

For example

ammonium chlaride

:;;::::=:::: ammonia

+ hydrogen chloride

NH3 (g) _+

NH4Cl (s) ( w:tiite solid)

HCl (g)

·.. {cptilourless gases).

·.

Energy change in reversible reactions: If a reversible reaction is exothc1·mic in one dit•ection it will he endothermic in the other. For example, hydrated copper (II) sulphate (CuS.04> SH:iO) needs energy supplied · in the forni of heat to give i!nhydrqus copper(II). sulphate. and water~ When -viater is ad
Hydrated copper(.(!) sUlphate

(+ heat energy ]

-7 f-

anhydrous copper(m sulphate

+water

··chemical Equilibrium __ _ When the rate offorward reaction = rate of backward reaction, the· reaction is said be at equilibrium.· · ·· . At equilibrium, the concentration of reactants and products does not change, - tn fact, both the forward and backward reactions are stilhaking place.

Factors affecting the position of equilibrium

Effect 'on "equilibrium &fthe.reailon:

Change In concentration

.A +

ofsubstano/ ·

B

-

'

c

+ D

'·'Proportion o(b!uid Dincreased,

1ncrease in concentration of AorB

I.e. equilibrium shifts to right

Increase In concentration

Proportion of A and B Increased,

of

Cor 0

·-

Le. equilibrium shifts

to left ,, i

Chemistry !GCSE

-107-

(Dr. Fathy Abde! Galli)

Increasing the temperature makes the reaction !!lOVe in the direction that takes in heat (.the err.do.theJun.i..c cUJr:e.c.tion). In other woras, a) For exothermic reactions, an increase in temperature favours the· reactants,. i.-e. ma:kes the reaction move to the ];eft. b) For ~ndothermic reactions, an increase in temperature favours the products, i.e. makes the reaction move to the right.

N2 2 502

+

3 H

+

02

<-T 2

2

so 3

T-=:==j">

2 NO

+

3,

.. 2 N.H 3

The effect of chanee in gres·sure r for <>'aseous reactions l

:

a:::z:::z:::=m:a=:a::JZJ;:;::.:u::;::::c=a:~at••====c.-:Sit.c-=e=-==•=*'!'.*"':::.:;:a:::;J:..t;:ia;::c;;r:xi2~=~~::t=ti=:Q::=az::.;=x:=o:::.:a:J::=c:

Increasing the pressure shifts the equilibrium in the direction in which there is decJI.e.4Ue in vohwre, i.e. th.e direction which produces fewer gas moles.

;;:==·z

+

NH (g)

3

2mol )> .Predict how the position of equilibrimii might ·change i f there were

an increase·in·the pressure on the f61lowin:g e-quilibria

+

CO (g) )>

__ 02

+ 2 H2 (g)

Why an increase in pressure does not affeCt the position of fhe following

equilibrium : 2NO(g) ·~-~~·-··············································· .. ························································~········

;::'.

·.-··.

Ch~mistry

(Dr. Fathy Abdel Galil) ·

-108-

IGCSE

Topic

11.

AIR AND WATER

PuM..QJ_c.atio n a 6 wa.:teJL Mppty : The water from rivers is. first. stored in reservoirs where the process of purification starts.

The water is still, so the larger

particles of dirt can settle out.

At the su:toface, oxygen· and sun- ·

light break down other impurities and kill some bacteria. The water from the storage rese:z::.voirs. is treated in two stages 1-

Filtration : ===:;::======== It is filtered through heds o·f fine sands to remove suspended (insoluble)

·-

solids. 2-

Chlorination : :ell:====-=-====== Then it is treated with chlorine to kill bacteria.

PUJte wa.:te.Jt c.a.n be ab.t.abted Mom .U, cut

U.6eo

.6e1t

wa.:teJL by liU.:tUJ..a:tWn, bu:t .:tJW,

expe.JU.<.ve p!toc.eo.6.

o6 wa.:teJL

Household tap water is free from

har~ful

bacteria and insoluble dirt,

but it is not pure ·in the chemist's sense because it contains gases and salts' in

solu~ion,,

In the. home . :

===.==========

1- Drinking 2- Washing 3- Cooking

Industry uses water in many ways, e.g. 1-

Much water is used for cooling. Power stations are built near i:ivers or coasts so that they cart. have continuous· supplies ·of. water for the cooling. towers;

2-

As a solvent: in many industries, e.g. paper industry;

3~

Manufacture of hydrogen and oxygen by ~lectroiysis of water.

Electrolysis of water Pure. water is a very poor conductor ofelectricity. To enqble water to conduct eiectricity better, some dilute sulphuric acid is added Hydrogen gas is fonned at the cathode and oxygen gas is collected at the anode. l :. i·":

(Dr. Fa thy Abdel Galil}

-109-

Chemistry 'IGCSE

Composition ·of air

-

Air is a mixture of gases :

nitrogen 78% (nearly 'A)

oxygen 21% Gust over \1;)

-·

----=====:;;;:tt----the remainidg ·1%

I_s~n.e~.riY:.?iu:ugon (a,.8~ble gc

+ a tittle carbon'diqxid.$and.Water vapour + sma!l~r amounts ofh~Jium;·neon, krypton and xe~on (the oth~r-6~blel'gases). : i

..

Sepalr'a..t.{_on a 6 oxygen a.nd /UX!wgen f/wm Uq!Ud lwr. Fractional distillation is used to separate the pure gases from one another ..

1-

Air is liquefied by compression._

2-

The liquid air is allowed to boil.

3-

The different components have. different boiling 'points, so ·they can be collected in turn as they boil aff,

(1) nitrogen . . (b.p. -: 196"C) (2). argon (b.p. -186"C) (3)

oxygen . (b.p. -183"C)

.·•·

U<> e.6 l-


- 110-

Chemistry IGCSE

o 6 o x_ygen : Pure, 'medical grade' oxygen is used in oxygen tents in hospitals for persons having difficu+ty in breathing normally because· of illness or unconsciousness.

2- In welding : . . . Acetylene (which is an unsaturated hydrocarbon) burns m oxygen to give a very hot flame "oxyacetylene flame" welding torch

c: Q) .i•

--'

UJ

z w __J

Ol

>-

X·

r::w

0

--'

3-

() <{

In making steel

FoJr.ma..:Uon o6 c.aJtbon d.{.oxJ..de : 1-

As a product of complete combustion of carbon-containing substances

CH

4

+ 2

o2 ,

~ C0

+2 H 20

2

methane (natural gas) C H 0H 2 5

+ 3 0 . 2

- 7 2 C0

2

+ 3 H2 0

(ethanol) .

Some 6uw, e.g. c.a.ndte w.:L:.:, aL6o pll:oduc.e a. depo.6.U o6 c.aJtbon (<>oo.t). TIUA p!tove.6 ..tha-t :the a»t l>!Lpply wa.o J.nllu66.f.cl.ent .to oxJ..d.{.ze aU. .the c.a.Jtbon .tn. :the· hydJr.oc.aJtbon 6ue.t ;td c.aJtbon d;_oxJ..de. rco 2 1. TheJLe .iJ, a.no.theJL p!toduc.;t a6 -i.nc.omplde c.ombUl>tion w!U.c.h you c.a.nno.t ue olt .~>me.tl. Th.iJ, .iJ, :the po.LbonoU1> :9a..6 c.a.Jtbon monoude [CO]. When pebt.ol .{..6 b!Litnt bi :the c.aJt wgine, ;the exllO.ll..il.t ga.<>e-6 c.on:tain .~>orne c.aJcbon ·monoude, <>orne !Litbwr.n:t hydltoc.a.Jtbonll· a.nd .iome .6oo.t -i.n a.drUtion ;to .:the ha.Jtmle-6.6 pJtod!.tU!> c.a.Jtbon d.toude and Wll.teJL.

2-

As a product of respiration : During breathing, some of the oxygen in the air is used up, and

C0 2 , water and heat energy ·are produced.

-111-

Chemistry I GCSE


Manufacture of ammonia by the Haber process : . Ammonia is made by

~yn.theo.U,

i.e. nitrogen and hydrogen·are

combined together.

1.

Nitrogen is obtained from the air.

2.

Hydrogen in now obta·ined from methane (natural gas). Hethane is heated with steam over a nickel catalysc

CO(g)

+

3 H (g) 2

> The following is the equation of formation of ammonia from Its elements, nitrogen and hydrogen:

+ i.

1NH3 (g)

The reaction is exothermic.

ii. The reaction is reversible.

)>

Conditions: temperature: 450°C pressure: 200 atmosphere catalyst: .iron

Ammonia is liquified by cooling. The unreacted gases are recycled.

:> 1. 11.

Uses of ammonia Making fertilizers Making nitric aCid

. Chemistry IGCSE

- 112-

(Dr. Fa thy Abdel Galil) =:

Ammonia in the Laboratory l.

Ammonia is a colourless; choking gas, which is. formed whenever· an ammonium salt is warmed with an alkali. For example• :

NH,Cl(s) . + NaOH(aq) ____,.. NH 3(g) ammonium sodium ammonia chloride hydro:x:ide

+ NaCl(aq) + H 20(1)

~p

sodium chloride

water

red litmus paper

:unmonium _ _____:~,.y chloride

t

warm

2.

Ammonia is very soluble in water and· aque·ous ammonia is .formed,. which is a weak alkali.

NH (g)· + 3 >-

+

~---these

H 0(!) ---+NH 08(aq) 2 4

ions make the solutionalkaline

Since ammonia is an alkali, it will neutralise adds to make ammonium salts. Ammonia +

nitric acid

---+

ammonium nitrate

Fertilisers

1. Fertilisers are substances, which added to soil to promote plant growth. 2. .The major plant nutrients include nitrogen (N), phosphorus (P) and potassium (K). 3. Nitrogen is the most important of the three elements because plants use it to make oroteins. Nitrogenous fertilizers: Ammonium nitrate Ammonium sulphate Ammonium phosphate Urea

NB4N03 (NB4)2S04 (NB4)3P04 CO(NH2)2

4. Many fertilisers contain phosphorous and potassium compounds as well as nitrogen compounds. These mixed fertilizers are called 'NPK' fertilisers.

16.8.24

NPK FERTILIZER

- 113-

Chemistry .!GCSE


AIR. POLLUTION

Apart from the gases normally _found in air, other gases such as sulphur dioxide, oxides of nitrogen, and carbon monoxide can be present. These gases can cause air pollution and are called po~.

Common pollutants in the air 1.

Carbon monoxide, CO : Carbon monoxide is produced by the .·incomplete combustion of carbon con~aining

fuels. Much of carbon monoxide comes from the in-

complete combustion of petrol in car engines.

CaJLbon monoxide .U po.UonolLb ga.;, :thtLt pll.even;U ha.emogtobbt .<.n _.the btood t)Jtom c.b.oo:r.bbtg oxygen. A:t a. tevet ot) H, c.aJtbon monoxide w.Ut k..U..e.- qc:U.c.kl.y; a..t toweJt levw J.;t c.a.Mu hen.da.c.hu a.nd d.<.zz.<.nu.o. Bebtg c.oloi11!1.U.6 a.nd odoUJLteM, c.Mbon monoxide g.<.vu no wa.Jr.nhtg

2.

on

-U:.-6 pJtUenc.e~

Sulphur- dioxide,

so 2

:

Fossil fuels (coal and oil) always contain sulphur. When burned, sulphur dioxide is formed. Factories and power stations burn coal, which contains sulphur. They send sulphur dioxide int-o the air.

Sutphwt d.<.o xide. c.a.Ub u bJr.a nc.hd.u a.nd .tung d.<.<> ea.<> u • In .the. uppeJt a..tmo.opheJte., i l -Jtea.W wd.h. wa.teJt :to 6oJun a.dd JuU.n.

3.

Oxides of nitrogen : When fuels are burned in the oxygen of the air, nitrogen is also present. At high temper-ature, the result_, some nitrogen with oxygen.

Nitrogen · + oxygen

--l>-

nitrogen· monoxide

~

2 NO(g)

Nitrogen monoxide + oxygen -nitrogen dioxide 2 NO(g)

combines

(Dr. Fathy Abde[ Galil)

- I 14-

Chemistry IGCSE

l·

About 30 - 407. of the oxides of nitrogen in the air come from car exhausts. Other sources of nitrogen oxide pollution are factories and fires.

NO .i..6 hJ.g hty c.aM.o~>.i.v e and ;to x.J..c.. 2 Ox.J..dv, a6 n..{.;t!togen. fuM.tve .i.n. wa:te.Jt ;to 6oJUn n.J..t;Uc. ac..i.d lead.i.n.g :to ac..i.d /W.{_n..

Catalytic removal· of oxides of nitrogen from car exhausts : Catalytic convertors are now ·being fitted in the exhaust of cars·,

where the toxic gases are converted in the presencR of a catalySt

into carbon dioxide and nitrogen.

exhaust from

of car

eng ina ' ·..

~\

catalytic converter Nitrogen monoxide

+

2 NO(g)

+

carbo~ ~·nitrogen · + monoxide

carbO:n dioxide

Ca:ta.e.y:Ue eon.ve.Jt:toM !Le.qt.Wte.d :the. Me o6 l11'11.eade.d pe;t:Jtol.

4.

Lead compounds A lead compound called tetraethyl lead·is added in small quantities to petrol to increase the octane number·of petrol. When the-petrol

burns in the engine, lead compounds are released from car exhaust.

Lead c.ompou.nd!.. Me. n.Vtve. po.Won.~>. In. pa!L:Uc.ulM., ·:the.y c.an. eaMe. b/W.{_n. damage .i.n. young c.hild!r.e.n.. The main way of preventing pollution from compounds of lead is the use of lead-free petrol (unleaded petrol).

Chemistry I GCSE

- 115-

(Dr:. Fathy Abdel Galil)

Acid Rain

Acid roln 1 I

Harmful effects of acid rain l.

Acid rain (pll

2.

It removes minerals from the soil and increases the acidity of

=

4) makes lakes too ncidic £or fish to live in.

the soil. 3.

Acid rain attacks construction materials such f!S limestone and

4.

Acid rain can speed ujJ corrosion-of metals.

It is important to control the acidity in soil. Lime [CaOJ or slaked lime [Ca(OH) J are used for neutralizirt(l acidic soils. 2

Finding the acidity of the soli :

I. 2. 3. 4.

A !te.p!Le..;e.n.ta.Uve. .6a111pte. o6 :the. .bOil ll. e., 6Jtont cU66e.Jte.I'Lt hl:tu o 6 .tfte 6le..tdl l.6 :tah.w. Wa.te.Jt .U a.dc(e.d :to .tlte
- ll6-

Chemistry IGCSE


!;

[:

Topic 12.

SULPHUR

A non-metallic element, yellol" solid, .. with low m.p., ll9°C. Large

amoun~s

are produced each year by mining as it is used to

produce sulphur dioxide.

Sources :

a-

Large amounts found in certain volcanic regions of the world.

b-

From sulphide ores [e.g. zinc blende] •

c-

Under ground deposits in the United States extracted as. liquid by pumping heated water into the sulphur depos.it.

Sulphur·dioxide, S0

:

2 =======a============== Acidic :gas. produced by burning sulphur in air S(s)

+

1-

As a. food presecvative

2-

B'leaching wood pulp

3-

Making sulphuric acid, H so 2 4

Food passed through an atmosphere of sulphur dioxide. The gas kills bacteria that could spoil the food or be a danger to human health.

When wood has been broken down to a· pulp ·it has a brown colour. In order to make. white. paper from the pulp it has to be bleached by passing sulphur dioxide through it. •

'

-117-

Chemistry IGCSE

(Dr. Fa thy Abdel Galli)

Sulphuric . acid ·is mad'e by the Con.ta.c.-t PMce6.6. This has 3 stages a)

Sulphur is burnt in air_ to ·make sulphur dioxide

I· b)

S(s)

+

Sulphur dioxide and.more air are reacted together. );>

Conditions : temperature: 450°C ,, catalyst: vanadium(V) oxide ; pressure: 2 atm. (for circulation ofgases),. (no need for high pressure] 2 S0 .(g) 2

+

i>ul.phwr. cU..ox.J..de . c)

o2 (g)

2

01(g)

so

3

(g).

;,Ul.phliJr. .

.oxygen 6iWm tWt.

ruo x.J..de

1/t :tfieblly, 46 i>ul.phwr. :tJ;;;l_ux.J..de £6 rUbi>ol.ved .:l.ll. Wod:eJL, L>u1.plu.vc.tc. a.c:id .U pJwduced•. Ba:t .thU .U. no.t dime in p}(O.c.tic.e .

:toa ex.o.the)!Jn)_e a.nd ·

on a. .ta.Jtge .6.c.al.e beaa.u.6e .:the Jt:e.a:c.tioir M boili :the <.ul.phwrJ.c. a.cU pMdU;c.ed.

. •....

.{.- · The <.iLtplit.vr. ruo:dde -M rUb.ool.v-e:d fi.i.Mt. in c.anc.e.n..tJUl:ted ;,Ul.phwUc. a.dd :to 6ollm ol.e.um. S0 (gJ 3

+

.6 u.tphwr.

..tliJ..o x.J..d.e ..U-

H:zSb4 (IJ - ·· -.> H2SzLl 7 (1) .6 u.tphwrJ.e

a.eld

-.- .->

d ··

0-<.-eunl

1he ol.eum .U then d.U.t.cted wUh the eoJUr.:ic:t·. amoiut:t o6· wa.teJL :to pJwduc.e ecmc.e:J1:tlu;(;te.d.L>u1.phwr..i,e a.ci.d. H s o (1) . + 2 2 7

ol.eum

H 0(0 2

wa.teJL.

-~>

2 H so (!} 2 4 .6 ul.phwr..Le a.c.f..d

Since ·all three of these ·r·eaC:tiona are. exothermic, the whole process

prod~ces heat en.e.rgy, The fact that enetgy is ·produced rather than . ' ;

'

needed means· that sulphuric acid can be produced· cheaply.

i- in-making :t~rtilisers (!'.g. ammonium sulphate) ii- ·iri making detergents iii- in making_paint;s i.:iii- ·iii. car batteries. Conc~e.d .6u1.p/w.JUe a.Ud .U paJ~y da.ngelloll.
Chem!.~try

IGCSE

(Dr. Fa thy Abde! Galli)

-11&-

Topic 13

CARBONATES

All carbonates a~e. insoluble in water exce~t-aodium, potassium and

l.

ammonium

carbon~te.

All cubonates .react wfth dilute aciqs, they all fizz and dissolve,

2.

giving off carbon dioxide and leaving a solut'ion of a .salt.·

Carbonate

+ acid

salt·;+- .water

+ 2 HCI(aq)

CaC0 3(s)

+ Cl!rbon.dioxide

. CaCI,;(-ilq). + ·HzO(lY.+ COi(g) . ·.. - ., ...

3 •. They decompose upon heating to f_orm_-llieta'J:._.oxide .. i:md:.-;:,ar)>,on dioxide.

--......,-.;:.

+ ·cbtfg}'

C\iO(s}

bia.c.li. Sodium and potassiurrt carbonate, however,~aretoo st<>bf~ to decompose ..

i.e. they.haye.high thermal stability. Suggest what is meant by th~ tenn thermal stability. . . .

·

............................ +···...... ·.. _.. ;; ....... ~---··

Limestone'.lime and- slaked lime : · .. ..

....

Name

Fonn!Jl?

•.

'.

caco · 3

Limes. tone Lime [Quick· Lime.]

. Ca{CF!l . ,. . 2·

Slaked Lime·

A solution of

CaO

~

..

'•

Chemical .. . .

Colour

Nam_e.~

Ca.rbOh~te .(alcium ... . .. Calc(um OXid~

Wh!~e

··--

..

.ca:icium

•.

..

Hy'droiddet .. · ··. .· ..·

calcit~m hyd'r
Co 2 gas it; bubbled

..

White

i:hrou~h 1i1!),i::.<'w~~~;~~-:ti\:~_-~@i'iihi~J.b;,;.~(;&um

carbo~S:te_ appears as a.-l{hi.c~ sifs{;-e~Ji~o~;:·:~~ 'i#i(!, ~$i~\l'i;':~(les 1 mi11W',

..-. ·.-

WJ:tlte ..

'.

Chemistry I GCSE

Calcium carbonate (Limestone) Formt.!la :

Usee :

~1


- 119-

An. important car:-bonate.

CaC0 3 M~nu6Q~~

o6

cement.

Cement ·is made by heating together limestone and clay.

b) - Ma.nu.6a.c..tWL~ o 6 .
c). neutralises acidity in the -soil

d)

Ma!1u.6a:~~ o{Um~ (C!CLtcWm ox.U!c).

Limestone is heated to a high temperature. It decomposes to calcium ol
.......... . Calciuin oxide has important

to calcium hydrol
u~ea.

2

water

+

.. ...... . •,

It can be re·adily convert·ed

(slaked lime],. by adding vater

---+ "---'-'r . .

calcium hydroXide (slaked· lime) Ca ( 0 H) 2

As both [lime and slaked lime.] form in water alkaline solutions,

they are used to : -

- Neutralize acidity in the soil · - Neutralize aciqic gases and industrial acidic wastes. Question· -:;:::====== The diagram shows a lime kiln.

· What are X and Y? y

X A

.lime

B

lime

slaked lime

c

limestone

lime

D

slaked lime

lime

.

limestone

heat

r

heat

t

heat

i:.

Chemistry IGCSE

(Dr. Fa thy Abdel Gal ill

- 120-

Topic 14.

ORGANIC CHEMISTRY

Org;mic chemistry includes the study of all carbon compoim.ds except the very simple ones such as

co 2 ,co

and carbonates.

The term 'organic' means.'living'. At first; organic chemistry was

the study of carbon chemicals from_planta and animals. Now it is "known that complex carbon compounds can be made artificially. Organic compounds are grouped into classes [families) such as hydrocarbons, alcohols, organic acids, ....

HYDROCARBONS Hydrocarbons are compounds containing hydrogen and carbon and no other elements. They are classified into alkanes

[saturated] and

alkenes [unsaturated). ALKANES They have single bonds between their carbon atoms, i.e. 6~ed

Name

N!-imberof Mol
methane

H I

CH,

1

.s.cw.o.tuJuiL !P;ynul.a.

H-C-H

I

H H ethane

C,H,

2

H

propane

butane

4

pentane hexane heptane octane ...

5

Gen eJ!a1.

6oJUnul.a

6 7

8

H H H H

I

c,H,

3

H

.I I H-C-C-H I I I

I

B-c-c~c-H

I I I

H H H H H H H I. I . I I H-c~c-c-c-H I I I I H H H H

C,HIO

. .. [n

= no,

of carbon atoms]

(Dr. Fa thy Abdel Gallll ·

- l2l-

Chemistry IGCSE

::·.

ALKENES

Alkenes are IJY!4a.:tulrLLted· ·_hydrocarbons, Le. they have a double bond between two carbon atoms. The simplest alkene. has only two carbon atoms. It is called ethene.

No. o6 c.Mban. Malec.ulM a.to/Jk\ 6aJUnula

Name

2

e,thene

. C2H4

StJw.ctWLa£.

H

H

I

I

H-C=C-H

H

I

3

propene

C3H6

6Ollmula

H

.I

H

I

H- C- C=C-H

I ·H

but-1-ene

4

but-2-ene

4

C4H8

C4H8

I!

H

I

I

I H

~

H

H

I

I

H

!I

I

I

H

H

H- C-C-C=C.,- H

t

l

H-C-C=C-C-H

I

I!

I

H

[ n = no. of carbon atoms]

Alkenes are characterized by. the presence of the double bond, which is called the 6un.c.:ti.pna£. g/f.oup.

ISOMERISM The alkene

c4a 8

.has two structures, but-1-ene and but-2-ene.

The different structures are called .i..bomeM.

· Isomers are compounds having the same molecular formula but. different structures

Chemistry IGCSE


-122-

ALKANOLS

[ALCOHOLS}

Alkanols can be.regarded·as. alkanes, in which one hydrogen atom is replaced by a hy~oxyi g~up

[OHJ,

This is called the

6unctidnal

g4oup. They are named after the alkane (with the same number of carbon atoms) [AN¥. -> 0 L].

No. o6 caJrbon a;tonu,

Name.

FoJrmul.a.

Sbw.e:tu!r.e. H

methanol

1

CH 0H 3

I

H-C-0-H I

H

ethanol

2

C H 0H 2 5

H H I I H-y-y-Cl--H H H H

propan-1-ol

3

c3H70H

I

H

I

H-C-C-"-C-0-H I f I !l H H H .0-H

propan-2-ol

3

c3H70H

I

I

H I

H-C-C-C-H f H

f . I H R

[n = no. of carbon· atoms}

0

Propan-1-ol and propan-2-ol are

H

·I

ihom~.

Th·e alcohols butall-1-ol and butan-2-ol .whi"h have the mol1>cular formula c H 0H are isomers. Write down their structural formulae. 4 9

...................................

. .................................... .

butan-1-ol

butan-2-ol

- 123-

Chemistry IGCSE

ALKANOIC ACIDS

(Dr. Fathy Abdel Galill

[CARBOXYLIC ACIDS]

They are organic acids and characterized by the presence'of the carboxyl group,

0

II

[ -G-0-H]

,

which is the functional group. They are named after the alkane (with the same number of carbon atoms) [A N

X -->

0 I C

ACID].

··---'---------------------------Name

No. o6 c.aJLbon

a..tom6

methanoic acid

1

0 II H-C-0-H

H I

ethimo:i.c. acid· [acetic acid]

propanoic acid

2

0

II

H-,C- C-O__:_H

I'

H

3

H H 0 I 1 II H-C-C-C-0-H . j

I

H li

Question :

==:.:::====== Draw the structure· of

butanoic. acid •

. . . . . . . . . . . . . .. . .. . . .... . . . .. . .. . . . ... .. .. . . . . . . .... .. . . .. .. .. . .. .. . ., ... Homologous Series

A 6a.m.Uy o 6 .shn.ilalt OJtganic. c.ompou.n.do wLth .s.i.m.W.vr. p!WpeJL.t)_ru due :to .the piLIUence o6 .the .sameJanc.tiona.t bu:p. AU membe!Lb Me ILepiLruen:ted by .the .same gene!La.t 6o.IUll , e.g. Cit ru, a.tk.enru,. a.t/Urno.U ••. A.s we go aLong a. homol.ogou.s .s rvr.J..ru :the bo.U'..<.ng a.nd me..Uhtg po-i.n:t.s o6

c.ompou.n.d.s · :gM,du:a.tl.y A.nc.ILe.M e.

-124-

Chem!s_try IGCSE


ORGANIC HALOGEN COMPOUNDS

These are compounds formed when hydrogen atoms in an alkane are replaced by halogen atoms.

chloromethane chloroethane

~

'I 7

H

8 8

H I

Br

H-f-C-C-Br

I

H I

H-f-9-y-H H H H

1-bromopropane

2 -bromopropane

1-bromopropane and 2-bromopropane are isomers; they have the same molecular formula c H Br. 3 7

FOSSIL FUELS

'

Fossil fuels [coal, crude oil, natural gas] have be,;n formed as a result of the decay of plants and animals that lived long time ago.

Fossil fuel

Appearance

What it contains

Natural gas

Colourless gas

Mainly methane (CH4 )

Crude oil [petroleum]

Dark brown liquid

A miXture of hydrocarbons, mostly alkanes

Coal

Black solid

Mainly carbon

Fossil fuels contain sulphur compounds, which form·acidic sulphur dioxide [S0 2 l when the fuel is burned (leading to

ac~d rain).

Coal, crude oil and natural gas are -vu1~-U..e ''-'~ d Jteoowr.c.eo, 1. e. nonrenewable source of energy. Fossil fuels and CO, emission:

co, is produced from burning fossil fuels, co, is a green house gas leading to

global warming.

- 125-

Chemistry lGCSE


·Fractional Distillation of Crude Oil Crude oil (sometimes called petroleum) is a mixture of alkanes. To make best use of oil, it is separated by fractional distillation into useful fractions according to the boiling range of the fractions._ The main fractions are :

fraction used as fuel in cars (C

(Kerosine)·

5

-

c 10 J

fraction for oil stoves and aircraft. (Cg - c16l fraction as a fuel for the engin·es of lorries, trucks and some cars (CJS - Czsl

crude oil

__...,_

fraction for making waxes and polishes (over c 2·5 J

heater Bitumen

fraction for making roads

In 6act, the demand on ughteJ~ oiUJ.moru, (pe;t;wl, piLIU1.66-i.nJ .U. gJtea.t~ .tha.n the .ou.pply fiJtam the fuWf..xti_on a6 CJw.de a.U.; . 6aJttuna.te.ty, .they ean be made 6Jtom .the hea.vi~ 6Mc..Uaru, by ci piweu;, CaU.ed eiUJ.c.IWtg.

Cracking The process of breaking longchained hydrocarbon molecules into shorter ones is called

c.Jt~Leking.

The reaction needs high tempeJtatulte and a

e~Lt~L./'.y;,t.

Al.kenes are

always formed as one of the products of cracking.

Chemistry IGCSE

long hydrocarbon molecule

Octane

-126-

~.temp. > c y;,J; .

_CJUl~-'-cl"-u·'-"'"ng-->


shorter alkane molecules

hexane

+

ethene

------>

Cracking is very Useful: 1. It' converts larger molecules from heavier, less useful fractions into smaller molecules that are useful as petrol [more benefit] 2. It also produces alkenes, which are very useful for making plastics. 3. Hydrogen gas could be also obtained during the cracking of alkanes. Cracking a liquid alkane: The following figure shows a simple laboratory cracking experiment. .The vapour of a liquid alkane is passed over a heated catalyst to make ethene. liquid alkane + ceramic wool

catalyst

delivery· tube

ethene

heal

heat

water

)>

Suggest the function ofthe ceramic wool_. .......... : ........ .

)>

The delivery tube is removed from the water before stop of heating. Suggest why this is done? ................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - .............. - ... - .... - -

- 127-

Chemistry IGCSE


ALKANES

Properties of Alkanes

1.

The first four alkanes are gases, the next fifteen are colourless liquids and the ·rest are solids.

2.

Like all hydrocarbons,, alkanes burn in air .giving co , H o and 2 2 heat energy is given out, so alkanes are useful as fuels.

+

CH (g) 4

2

o 2 (g)

(methane)

--)

··

C H (g) + 5 0 (g) 3 8 2

+

(propane)

3.

Alkanes are generally unreactive.

4.

Simple alkanes react with

ehta~e

gab

in presence of

!Lght.

Thus, when methane is mixed with chlorine gas in bright light, ehto4am~hane is slowly formed.

H

H

I H-c-H + Cl 2 I .

LL h't. g ·

>

I

H-C-Cl

I

[,{

H

mc:thanc

·chloromethane

Similarly,

+ ethane

Cl

£<.ght 2

·

+

HCl

hydrogen chloride gas

) · C H CI 2 5

+

HCI

chloroethane

This is called. s.ubstitution reaction because the hydrogen atom in methane molecule is replaced by chlorine atom.

Saturated hydrocarbons undergo substitution reactions.

Chemistry IGCSE


- 128-

f:~;

ALKENES Alkenes (e.g. ethene, propene) are produced in large quantities in industry from the larger molecules in oil fractions by the process of cna~g.

Properties of Alkenes Alkanes are members· of a homologous series, so they all show similar che"in.ical properties ..

They burn with bmok.IJ•.. yel-t_oW flame

l.

-->

+

:: ..

The double bond in alkenes make them Ve.JUj Jte.a.c.:ti.ve. They undergo

2.

a.dcU..:Uan Jte.a.c.:ti..!J no •

Unsaturate.d hydrocarbons undergo additior\ reactions:

[A]

Addition of hydrogen (hydrogenation) If ethene gas ·(unsaturated) in mixed with· hydrogen and is

heated over a catalyst (nickel), ethane (sa.tuni.ted) is formed •.

+ ethene ,

H;

H

H

I

I

I

Nl

~

k

"'"'"' H-C-C-H

c2 H 11

ethane ,

unsaturated (double bonds present)

c 2 H6

saturated (all singie bonds present)

Similarly,

+ propene

propane.

Generally,

Alkene (unsaturated)

+

hydrogen

Alkane (saturated)

-129-

Chemistry !GCSE


Making Margarine The molecules of the vegetable oils contain several double bonds; L e·. they are poiywua..:tww..ted~ By reacting them with hydrogen and a catalyst (nickel), they are made

-

saturated. This raises the melting point, so the liquid oil becomes a solid fat - m~ga4Ute. The process is called ~dening

o6 oilh.

Vegetable oil

+

Ni

hydrogen

catalyst

>

margarine

Large amounts of hydrogen are used in industry for making margarine. State another large scale use of hydrogen : . _;_ .. _... _.. ____ .. ____ _ [B]

Addition of bromine (Br 2)

J\lkenes reactwith a solution of bromine in water (~q~eoub bll.oin.Lne) , the red-orange colour of bromine goes colourless.

+

ethene -

H

H C=C-/

""'

H/

bromine

1,2-dibromoethane

--+

H H I I H-C-C-H I I

Br-Br

""'H

Br Br

red,--orange

colourless

colour

+

+

) C 3 ~Br 2

1,2-dibromopropane Similarly, ethane adds chlorine to form dichluroethane. Aqueous bromine (bromine ~ater) is used to test for a do~bf.e

bond. It works

~ith

any uMatukated moteeuf.e.

lzo- Row would you show by a chemical test that olive oil is unsaturated 1

........................... ,. ............................... -....................................... .

-130-

Chem.istry lGCSE

(C]

(Dr. Fa thy Abdel Ga!il)

Reaction with steam [Addition of water]

EthanoL is formed in the reaction between.~!en~ nnd bt~m at high temperature (250°C]. A catalyst is used (phosphoric acid]. ethene ·+

H..._

H

c.a.:ta.tyb;t )

water (steam)

/H

C= C / '-...

H H

+

H-0-H

H

C2H4

ethanol

->

I I H-C-G-0-H l l

HH

+

H 0 2

>

o

>

C H 0H 2 5

Similarly, i

+

C3H6

'

-,

H

2

ptop
steam

propene

C H 0H 3 7

Generally,

catalyst

Alkene

water

+

Alcohol

(steam)

);;. Shtc~ a wcd:e.ll ritaL~cu.t~ hM .b~w add~d to th~ doubL~ bond bt ill~n~, th~ Jtwc.:Uon .U. caLLed hyciM.:t[on, The. Jt~v_e.M ~. Jt~c.:Uon, L ~. e.l.-Zm-ln.ation a 6 wcd:e.ll moLe.cu.t~ 6Mm illanof. to 6o1Ull dhe.n~ .U. caf.f.~d de.hyciJw.:t.lon.

---::> c 2H 4 +

H 20

ethene Dehydration can be achieved by : (a-)

Heating the ethanol with excUb concen:tluLt~d <>u.tphwU..c

acJ.d [dehydrating agent]. {b)

[D]

Passing ethanol vapour over hot ~ o~de.

Reaction with hydrogen chloride gas-

H H +

HCI

------,)

I

I

I

I

H -'-C--C- Cl

H H chloroetnane

ethene

+

HCt

.· ..

-131-

Chemistry I GCSE

E]

(Dr. Fa thy Abdel Gatil)

_

Addition polymerisation [Making plastics)

F'o.tymvt-lb!Ltiott

is the -process in vhich many small molecules

(manam~) join together to ~ake a large molecule

molecule)

(macro-

which is called-pa.tym~.

The polymerisation is done at high-temp~e and pressure in presence of a

cata!.yJt.

H

H

I

H

I

C=C

I

H

I

H

I

I

C=C

+

I

H

H

I

H

l

+

l

-->- ...

C=C

I

~-~-t-6-d-d ... I

I

I

H

H

H- Pi H H H H

H

H

ethene [monomer] 11.6

Pa.ty (ethene)

I

H ·H· H

I

H

I

H

I

H

poly(ethene) [polymer]

b-~iI

I

H

H

n

is used to make plas.tic bags and plastic sheets.

HCIHCIHCl

H, n

H/

c=c

_,...CI 'H

I

I

I

I

I

I

I

I

I

I

I

I

_____,. · .. c-c-c-c-c-c · · . H H H H H H

chloroethene (vinyl chloride)

poly( chloroethene) (PVC)

Polykh.taJtae.thene) known as PVC is used to make. plastic bottles, floor tiles, raincoa-ts and electrical wire insulators.

I -Ht l CHJ c_:_c

n

I. I

propene

H.

H

n

poly (propene)

Paly(plwpenel is used to make plastic sheets, electric insulators and bottles.

Monomer: A small molecule which =n be polymerised (joined together) to make a polymer. Poiymer:

A macromolecule (large molecule) made by polymerising (joining together) ofmonomers.

-132-

Chemistry IGCSE

(Dr. Fathy Ab9el Galil)

.Examples o{ other addition polymers

Polymer

Monomer formula/Name H

I c=c I . \

Name

H

\

C 6H 5

poly(phenylethene) (polystyrene)

H

formula

f "t I

~

n

..

STYRENE (PHENYLETHENE) CN

\ I c=c I \

Poly(acrylonitrile)

+r 'tt c-c

I

H

H

pacKaging

c-c

c!H5

H

I

Uses

H

I

H

Synthetic fibre

n

ACRYLONITRILE F

\ I c=c \ I

F

F

poly{tetrafluroethene) or PTFE

F

tf-11 F

F

non-stick coating in frying pans

n

mRAFLUOROETHENE

P.ta.L>.UC-6 :

good

oJi

bad ?

i]QQ!!_t!Q{~ 1• Qu.de cheap 1 and eM ;i.y made

2• 3.

4.

s.

Ug hte.Jt than me.ta.l Uwr.ea.c..Uve, . They do no.•~ :coMo de .W c0t oiL wa.teJt. Many Me not a.66ected by .a.cJ:.dl, olr.. a.eJw.Ul, Vo not conduct hea..t olt dec:tJU.cfty 1 ;,o c.a.n be Med a.o

-Utbu1a.tolt.6

.

Can be mou:tded.1n.to any .;ha.pe and c.a.n be cowwr.ed.

§~!!_t!Q~ P.ta.L>tie-6 ca.lL6e pou.u.ti.on pJr..Ob.tem.; beC1UL6e: 1•

2.

They Me d1661c.u1.t .to d1opo1>e o6. P.la..!tic bag!> and Ca.JL.tonl> · do not Jtpt wh.en they Me .tlvr.own a.wa.y 1 1n o.tlvt woJull, 1 they Me non-:b1odegJUUia.b.te1 1. e. c..a.J1J!.ot .be degltaded by rri..cJtooJt.ga.n-Winl>1 1>owey pau.u.-te the env1Mnment; When they bwr.n, they aMen pltodu.ce ha.!tm6u.t gMel>: e.g. PVC give~> o66 6wne.~> o6 hydltogen ch.toJU.de when 1t buJ!Ji6.

;

. i.' ;.

- 133-

Chemistry IGCSE

(Dr. Fathy Abdel Gaiil)

.ETHANOL Making Ethanol for Industry -1- Hydration ofethene _ Addition of steam to ethene [obtained by the process of cracking] at'high temperature in pr~sence of a catalyst [see page 130] 2- Makin<> ethanol by fermentation: . b FeJutre.IU:ation

~s

the process where sugars (e.g.

vei:ted to ethanol and carbon

d~ox~de

gluco~_e)

by· enzymes present

~n

a.re con-:'··

yeast:.

-:·:

The process works best at

Sugar solution (e.g. glucose) C6Hli 0 6

37~C.

---,) . ethanol

+ carbon dioxide.

I.t .U, hlrpolda.nt :to plte;.ve.nt· aA.Jt 6Jtom. e.n:teJU.ng .the. Ji.~d.t.or~- vv,,; eL, e.:tlutno.i.c. add wUJ. be. 6oJtme.d. Ye.a.i>:t -c.an ortl..if pl(.odu.c.e. a .6o.tu.tion c.o~g I 0% e.tfutno.f... k6:teJt :tha:t, :the. ife.M:t d.i.v, 6Jtom atc.aho.f. po.i.,;ort.{.ng. · o:th~e.

The apparatus below can be used 1:0 ferment glucose •

. Air lock allows carbon dioxide to escape, butpre~ents air getting in, i.e. allows fermentation under · anaerobic conditions jar

yeast

+

glucose.

--1~::;:::::::;::::::~

+ .water

>

What technique is used to concentrate the aqueous ethanol? ... _.. __

Dur~ng s~nce

a fermentation process,

the reaction is

are also observed.

exotherm~c.

r~se·

in temperature is observed

Bubbles of a colourless. gas (C0 ) 2


- 134-

Chemistry IGCSE

A laboratory experiment to demonstrate the fermentation: sugar solution andyeast -~

limewater

Wine (contains about 10% ethanol) is made by fermenting grape juice. Beer is made by fermenting malt. Spirits (whisky, brandy, ..} contain about 30% alcohol. Biotechnology Microorganisms have been used in some methods of food-making fcit .many centuries. Today these methods are often referred to as examples of 'biotechnology'. One of the oldest kriown biotechnologies isferm(mtation. Properties of Ethanol 1. Colourless liq11id. b.p. 78°Cjrteutral to litmus.

2. Ethanol burns in air with a blue flame to form C02 and H 2 0 and heat · is given out.

3. Ethanol undergoes dehydra:tion and is converted into ethene when heated with. concentrated sulphuric acid.

Uses of Ethanol

1. As a: solvent

2. As a fuel

3. In alcoholic drinks

Uses of methanol (toxic)

1. As a solvent

2. As a: fuel

- 135-

Chemistry IGCSE

Ethanoic acid

>


H Q' I II H-C-C-0-H I

-

H Ethano-ic acid is usually called acetic acid . (from the Latin word for vinegar -

'acetum'). Vinegar is a 5% solui:;Lon of --.eth~noic acid.

Formation of. Ethanoic Acid from Ethanol a)

£L~xi~~!::!:~:;-~:!,_t:!!_~tmosEheric ~?.'X~:;__:

Vinegar is made by exposing ethanol to the air in the presence of' bacteria. Ethanol is o~ed to ethanoic acid.

~ ~

H

H-C-C-0-H I I H H Wta.noi.

I

+

0

0 II

H-C-C-0-H

2

I

+

H

e.tha.no.i.c. o.c..i..d

This is another example of 'biotechnolo'gy'.

~~g~1=~g=,;, Suggest a reason·why wine goes 'sour' when .left open in air·?

..................................................... •.............. ............................................ . .. . .. .. . .. .. . .. . ........................ ,. ....................... · ........................... . ~

_

b)

Ethanol can b~ ox..Ui..U,ed.much more quickly-iri the laboratory by _heating it with an.o~.i.ng

agent

such as potah~ium

d.i.c.hAomo.te{VT}

(adllified with sulphuric acid). On heating the colour changes from

o.lta.n.ge

to. gltee:n.. In other words, when aqueous potassium

dichromate (VI) is

Jteduc.ed,

the colour changes from ••••••••••..•

to ................... .

Generally: alcohol [alkanol]'

oxidation carboxylic ac~d

Oxidation of methanol gives _........... . Oxidation of propanol gives ............ .

Chemist1·y IGCSE

- 136-


.. :

Et}w.no.i..c. a.c.i..d .i..b a. wea.k. a.c.i..d. Ethanoic acid (and all carboA-ylic acids) is a weak acid, i.e. partially ionized in aqueous solution.

~~~~;!;-£liH~=,; The pH value of ethanoic acid is ..•..••••••••••• ; •••••••••••••••••. What is the colour produced on adding drop of universal indicator to ethanoic acid ?

.................... • ..................................................... .

Ethano.i..c. a.c.i..d .i..b juJ.:t Uke_ MCJ o.theJt a.c.i..d. It reacts with * Metals to form a salt + hydrogen

* *

Bases and alkalis to form a salt Carbonates to form a salt

+ water

+ water + carbon dioxide

In each case the salt is:c.alled ethanoate.

Examples_:

1>- ethanoic add

+ sodium hydroxide --* sodium ethanoate + water

1>- ethanokacid

+ sodium carbonate --* sodium ethanoate + water + carbon dioxide

However, the reaction of ethanoic acid is slower than of other acids such as hydrochloric acid or sulphuric acid. Why? ...... ········· ............................................................................................ );>

Differentiation between ethanol and ethanoic acid

test );>litmus paper );> sodium carbo-nate >potassium dichromate );>lighted splint

ethanol

ethanoic acid

no colour change no reaction . orange -7 green catches fire

turns red effervescence -7 C02 no colour change does not catch fire

Chemistry IGCSE

[Dr. Fathy Abdel Gaiil)

- 137-

Esters: Organic acids like ethanoic.acid react with alcohols to form compounds called eh£~ in a reaction co~~only called an

organic acid + [carboxylic acid]

'

alcohol

ehte4i6ieation.

ester

+

water

e.tha.no.t is heated with e.tha.no.Lc. a.c..Ld in the presence of .Ou.tphuh.Lc. a.c..Ld as a catalyst, the ester ethy.t etha.noa.£e is formed.

When

ethanoic acid +

ethyl ethanoate + water

ethanol

·•·.

~

1;0

~ ~

.. -.

H

+: H;O-C-C-H \~ .. "· ....... · I I. ;oH:: H H

H-C-C

I

H

·· ....

~

I

0 ,--the ester linkage

1/

H-C+C ·I \

H\

'

l

H I

H

H

H

I 'o-+c-c-H + H2o \..........J I I

Similarly: ethanoic acid + methanol

~

methyl ethanoate + ·water

Ethylethanoate has a characteristic pleasant smell. Many fruits' smells are caused by esters. Artificial flavouring are usually mixtures of esters. The reverse reaction of esterification is called hydroly~is.

j ester + water

-·-:t

carboxylic acid + alcohol

Fats and Vegetable Oils Fats and oils are important constituents"of our· food. They are e..6te.Jr..6 ,. i.e contain the ester linkage [::-CQQ;..]

Making Soap (Saponification)

Soa.p

is produced by heating vegetable oils or animal fats with

sodium hydroxide solution (i.e.

.

alka.tine

Fats I oils +sodium hydroxide

~

-.-

hy~d.tybib).

soap + glycerol

Chemistry IGCSE


- !38-

Carbohydrates

1-

A family of energy foods including starch and sugars.

2-

These compounds consist of carbon, hydrogen and oxygen,_ the hydroge~

and oxygen atoms are present in the sariie ratio as in

wa.ter.

3-

Sugars are carbohydrates which are soluble in water and taste ·sweet.

The chemical name for ordinary sugar is .6UCJl0.6e..

LQcto.6e. is the sugar found in milk, and fructose occurs, with

other sugars, in fruit juices. and honey.

CaJtboh!JdN:t;te.6 a.o po.tymeM : [ complex carbohydrates

1

Starch molecule consists of a long chain of g;Lucose molecules .• Glucose HO--Q-OH (a monomer) can be j6ined by in a l.ong chain to form starch (a polyl!ler) by condensad.on ]>o.lymerisation.

glucose rolecules .

li

(monomers)

condensation polymerisation

hydroly•h

-o -c=J- o -c:::J- o· --c=J- o- + H2o starch (polymer)

Ac.JJJ. hyd.Jw.tif.6.U

o6 c.a.JWohydJw.;tu,,

e.g. starch :

.Starch ·can be hydrolysed into gl.ucose molecul.es by boiling with dilute hydrochloric acid starch

hydrochloric acid boiling

I> glucose (simple sugars)

Chemistry lGCSE

- 139-


Proteins Proteins are natural macromolecules. Amino acids are the monomers from which proteins are made. Formation of a p;lrt of protein chain : When proteins are formed, an amino group from one amino add reacts Vlith the carboxyl group from another (VIith elimination of water). This-process can continue repeatedly tc produce long chain (i.e. macromolecule).

H

0

I

II

Ii.

0

.. .:-····· ... \ II H-N-i=t-c
..

..

....

amino acid

condensation polyrner!satlon

H

.

···I

protein.

·

~

·-

amino ac~d

l1

hydrolysis

H

1

0

·

II

·

H-N-c::J-C-N---~- C~OH

·

~~ amide linkage

The linkage between the amino acids in a protein is called amide (peptide) linkage. Proteins are broken down by hydrolysis into their ?mino acids. This process. occurs VI hen protein foods are digested. This needs enzymes (biological catalysts). )> In laboratory,- proteins can be hydrolysed into their amino acids by heating with dilute · acids (e.g; HCL or HiS04). !>-- The products of the hydrolysis of proteins and carbohydrates can be separated and identified by chromatography. The products. are colourless so need spraying a locating agent to be seen on the chromatogram. )> )>

These constituents of food can all be hydrolysed by boiling ·with acid or alkali. · linkage

· consliluent of food protein

product of hydrolysis

-

fat complex carbohydrate

~

Complete the table.

[5]

Chemistry IGCSE


- 140-

CONDENSATION POLYMERISATION Occurs when a small molecule such as >
s·yuthetit Macromolecule~ Polyesters Polyesters (e.g.

~~ylene,

a man-made

fibre.) are polymers which

contain ester linkages. Polyesters are formed when

HO-

)(

? .···.-···-c.---....--·. c----[B- c-:mr· + : .H.P OH . .. . -Q. .

nylon., a.m{.de UnfW.g V>.

Polyamides (e.g. contain

r:Uo-cl..dl. and cUa.tcofto.U combine together.

Polyamides. are formed when

a

man~ made

fibre) are polymers which

clia.cl..dl.· and cU.am.{_nu, combine· together.

.

~

H .

........~.· I

. .

H i

(H-;- N-0~N- II

--

.

d

H I _l_ . c~I22Ld:....C-N-: 0 -N)"

~ II

\

..

Nylon a.nd i:.eJtyi.R;n.e Pi!.a.te.<.n a.nd <>i:aJc.c.h

P:W::l

. CUte

Me

0 .11

. .

H I

.

. .

·

.

n

examplV> of, syn.the.ilc ma.c.Jwmotecu.LV>. na.tu!utt ma.cJr.omo!.ecu.e.u.

ll> What is the difference between addition polymerisq:tlon and condensation polymerisation? ·

---------······-········--------------·-----·---··--···----·-----··----··--------··-----·-··--··:.--------~; ................... [2]

Cambridge IGCSE Chemistry Syllabus code 0620

1. Introduction ..................................................................................... 2 1.1 1.2 1.3 1.4

Why choose Cambridge? Why choose Cambridge IGCSE Chemistry? Cambridge International Certificate of Education (ICE) How can I find out more?

2. Assessment at a glance .................................................................. 5 3. Syllabus aims and assessment ....................................................... 6 3.1 3.2 3.3 3.4 3. 5 3.6

Aims Assessment objectives Scheme of assessment Weightings Exam combinations Conventions

4. Curriculum content ........................................................................ 12 5. Practical assessment. .................................................................... 28 5.1 Paper 4: Coursework 5.2 Paper 5: Practical test 5.3 Paper 6: Alternative to Practical

6. Appendix ....................................................................................... 36 6.1 6.2 6.3 6.4 6.5 6.6 6. 7 6.8

Grade descriptions Periodic Table Notes for use in qualitative analysis Safety in the laboratory Glossary of terms Mathematical requirements Resource list Forms

·-·------·-·---·-----------------------

1.1 Why choose Cambridge? University of Cambridge International Examinations ICIEJ is the world's largest provider of international qualifications. Around 1.5 million students from 150 countries enter Cambridge examinations every year. What makes educators around the world choose Cambridge?

Recognition Cambridge IGCSE is internationally recognised by schools, universities and employers as equivalent to UK GCSE. Cambridge IGCSE is excellent preparation for A/AS Level, the Advanced International Certificate of Education IAICEJ, US Advanced Placement Programme and the International Baccalaureate (I B) Diploma. Learn more at www.cie.org.ul
Support CIE provides a world-class support service for teachers and exams officers. We offer a wide range of teacher materials to Centres, plus teacher training (online and face-to-face) and student support materials. Exams officers can trust in reliable, efficient administration of exams entry and excellent, personal support from CIE Customer Services. Learn more at www.cie.org.uk/teachers.

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Not-for-profit, part of the University of Cambridge CIE is part of Cambridge Assessment, a not-for-profit organisation and part of the University of Cambridge. The needs of teachers and learners are at the core of what we do. CIE invests constantly in improving its qualifications and services. We draw upon education research in developing our qualifications.

2

1.2 Why choose Cambridge IGCSE Chemistry? Cambridge IGCSE Chemistry is accepted by universities and employers as proof of essential chemistry knowledge and ability. As well as a subject focus, the Chemistry syllabus enables students to: •

better understand the technological world in which they live, and take an informed interest in science and scientific developments

•

learn about the basic principles of Chemistry through a mix of theoretical and practical studies

•

develop an understanding of the scientific skills essential for further study at A Level, skills which are useful in everyday life

•

learn how science is studied and practised, and become aware that the results of scientific research can have both good and bad effects on individuals, communities and the environment.

1.3 Cambridge International Certificate of Education (ICE) Cambridge ICE is the group award of the International General Certificate of Secondary Education (IGCSEI. It requires the study of subjects drawn from the five different IGCSE subject groups. It gives schools the opportunity to benefit from offering a broad and balanced curriculum by recognising the achievements of students who pass examinations in at least seven subjects, including two languages, and one subject from each of the other subject groups. The Cambridge portfolio of IGCSE qualifications provides a solid foundation for higher level courses such as GCE A and AS Levels and the International Baccalaureate Diploma as well as excellent preparation for employment. A wide range of IGCSE subjects is available and these are grouped into five curriculum areas. Chemistry falls into Group Ill, Science.

Learn more about ICE at www.cie.org.uk/qualifications/academic/middlesec/ice.

3

1.4 How can I find out more? If you are already a Cambridge Centre You can make entries for this qualification through your usual channels, e.g. CIE Direct. If you have any queries, please contact us at [email protected].

If you are not a Cambridge Centre You can find out how your organisation can become a Cambridge Centre. Email us at [email protected]. Learn more about the benefits of becoming a Cambridge Centre at www.cie.org.uk.

4

Cambridge IGCSE Chemistry Syllabus code 0620 Cambridge IGCSE Chemistry candidates are awarded grades ranging from A* to G. Candidates expected to achieve grades D, E, F or G, study the Core Curriculum only and are eligible for grades C to G. Candidates expected to achieve grade Cor higher should study the Extended Curriculum, which comprises the Core and Supplement Curriculums; these candidates are eligible for all grades from A,. to G. All candidates must enter for three papers.

Paper 4 Coursework weighted at 20% of total available marks

Paper 5 1 hour 15 minutes Practical test weighted at 20% of total available marks

1 hour Paper 6 Alternative to Practical paper weighted at 20% of total available marks

Alterations in the syllabus assessment. content and practical assessment sections for 2011 are indicated by black vertical lines on either side of the text.

5

3.1 Aims The aims of the syllabus listed below describe the educational purposes of this examination. The aims of the syllabus are the same for all students and are not listed in order of priority. The aims are:

1.

to provide a worthwhile educational experience for all candidates, through well-designed studies of experimental and practical science, whether or not they go on to study science beyond this level

2.

to enable candidates to acquire sufficient understanding and knowledge to

3.

•

become confident citizens in a technological world, able to take an informed interest in scientific matters

•

recognise both the usefulness and the limitations of scientific method, and appreciate its applicability in other disciplines and in everyday life

•

be suitably prepared for studies beyond IGCSE in pure sciences, in applied sciences or in sciencedependent vocational courses

to develop abilities and skills that •

are relevant to the study and practice of Chemistry

•

are useful in everyday life

•

encourage efficient and safe practice

•

encourage effective communication

4. to develop attitudes relevant to Chemistry such as •

concern for accuracy and precision

•

objectivity

•

integrity

•

enquiry

•

initiative

•

inventiveness

5. to stimulate interest in the environment and caring for it 6.

to promote an awareness that •

scientific theories and methods have developed, and continue to do so. as a result of co-operative activities of groups and individuals

•

the study and practice of science are subject to social. economic. technological, ethical and cultural influences and limitations

•

the applications of science may be both beneficial and detrimental to the individual, the community and the environment

•

science transcends national boundaries and that the language of science, correctly and rigorously applied, is universal.

6

3.2 Assessment objectives The three assessment objectives in Cambridge lGCSE Chemistry are:

--

A

Knowledge with understanding

B

Handling information and problem solving

G Experimental skills and investigations A description of each assessment objective follows.

A:

Knowledge with understanding

Students should be able to demonstrate knowledge and understanding in relation to 1.

scientific phenomena, facts, laws, definitions, concepts and theories

2.

scientific vocabulary, terminology and conventions (including symbols, quantities and units)

3. scientific instruments and apparatus, including techniques of operation and aspects of safety 4. scientific quantities and their determination 5. scientific and technological applications with their social, economic and environmental implications. Curriculum content defines the factual material that candidates may be required to recall and explain. Candidates will also be asked questions which require them to apply this material to unfamiliar contexts and to apply knowledge from one area of the syllabus to knowledge of a different syllabus area. Questions testing these objectives will often begin with one of the following words: define. state, describe, explain or outline (see Glossary ofTerms).

B:

Handling information and problem solving

Students should be able, in words or using other written forms of presentation (i.e. symbolic, graphical and numerical), to 1.

locate, select. organise and present information from a variety of sources

2.

translate information from one form to another

3.

manipulate numerical and other data

4.

use information to identify patterns, report trends and draw inferences

5.

present reasoned explanations for phenomena, patterns and relationships

6.

make predictions and hypotheses

7.

solve problems, including some of a quantitative nature.

7

Questions testing these skills may be based on information that is unfamiliar to candidates, requiring them to apply the principles and concepts from the syllabus to a new situation, in a logical, deductive way. Questions testing these skills will often begin with one of the following words: predict, suggest, calculate or determine. (See the Glossary o!Terms.)

·C:

Experimental skills and investigations

Students should be able to 1.

know how to use techniques, apparatus and materials (including following a sequence of instructions where appropriate)

2.

make and record observations, measurements and estimates

3.

interpret and evaluate experimental observations and data

4.

plan investigations, evaluate methods and suggest possible improvements (including the selection of techniques, apparatus and materials).

3.3 Scheme of assessment All candidates must enter for three papers: Paper 1; either Paper 2 or Paper 3; and one from Papers 4, 5 or 6. Candidates who have only studied the Core curriculum, or who are expected to achieve a grade D or below, should normally be entered for Paper 2. Candidates who have studied the Extended curriculum, and who are expected to achieve a grade C or above, should be entered for Paper 3. All candidates must take a practical paper, chosen from: Paper 4 (Coursework), Paper 5 (Practical Test), or Paper 6 (Alternative to Practical).

8

Paper 1

45 minutes A multiple-choice paper consisting of 40 items of the four-choice type. This paper will test skills mainly in Assessment objectives A and B. Questiolrs will be based on the Core curriculum and will be of a difficulty appropriate to grades C to G. This paper will be weighted at 30% of the final total available marks.

Paper 2

1 hour 15 minutes

Paper 3

1 hour 15 minutes

Written paper consisting of short-answer and structured questions.

Written paper consisting of short-answer and structured questions.

Questions will be based on the Core curriculum and will be of a difficulty appropriate to grades C to G.

Questions will be based on the Extended curriculum and will be of a difficulty appropriate to the higher grades.

Questions will test skills mainly in Assessment objectives A and B.

Questions will test skills mainly in Assessment objectives A and B. A quarter of the marks available will be based on Core material and the remainder on the Supplement.

80 marks

80 marks

This paper will be weighted at 50% of the final total available marks.

This paper will be weighted at 50% of the final total available ~1arks.

1 hour 15 minutes

Paper 4*

Paper 5*

Coursework

Practical Test

Alternative to Practical

School-based assessment of practical skills.**

Questions covering experimental and observational skills.

Written paper designed to test familiarity with laboratory based procedures.

weighted at 20% of the final total available marks



9

Paper 6*

1 hour

*

This component tests appropriate skills in assessment Objective C. Candidates will not be required to use knowledge outside the Core curriculum.

** Teachers may not undertake school-based assessment without the written approval of CIE. This is only given to teachers who satisfy CIE requirements concerning moderation and who have to undergone special training in assessment. CIE offers schools in-service training in the form of occasional faceto-face courses held in.countries where there is a need, and also through the CourseworkTraining Handbook, avail~ble from CIE Publications.

3.4 Weightings A: Knowledge with understanding

50% (not more than 25% recall}

B: Handling information and problem solving

30%

C: Experimental skills and investigations

20%

Teachers should take note that there is an equal weighting of 50% for skills (including handling information, problem solving, practical, experimental and investigative skills} and for knowledge and understanding. Teachers' schemes of work and the sequence of learning activities should reflect this balance, so that the aims of the syllabus may be met, and the candidates fully prepared for the assessment.

A: Knowledge with understanding

25-30

48-52

0

47-54

B: Handling information and problem solving

10-15

27-32

0

26-33

0

0

40

20

C: Experimental skills and investigations

10

3.5 Exam combinations Candidates can combine this syllabus in an exam session with any other CIE syllabus. except: •

syllabuses with the same title at the same level

•

0652 IGCSE Physical Science

•

0653 IGCSE Combined Sde.nce:

•

0654 IGCSE Co-ordinated Sciences (Double Award)

•

5124 0 Level Science (Physics. Chemistry)

•

5126 0 Level Science (Chemistry, Biology)

•

5129 0 Level Combined Science

•

5130 0 Level Additional Combined Science

Please note that IGCSE, Cambridge International Level 1/Level 2 Certificates and 0 Level syllabuses are at the same level.

3.6 Conventions (e.g. signs, symbols, terminology and nomenclature) Syllabuses and question papers conform with generally accepted international practice. In particular, the following documents, published in the UK, should be used as guidelines: Reports produced by the Association for Science Education lASE): 51 Units, Signs, Symbols and Abbreviations (1981) Chemical Nomenclature, Symbols and Terminology for use in School Science (1985) Signs, Symbols and Systematics: The ASE Companion to 16-19 Science (2000).

Litre/dm' To avoid any confusion concerning the symbol for litre, dm' will be used in place of I or litre.

11

The Curriculum content below is a guide to the areas on which candidates are assessed. It is important that, throughout this course, teachers should make candidates aware of the relevance of the concepts studied to everyday life, and to the natural and man-made worlds. In particular, attention should be drawn to: •

the finite life of the world's resources and the need for recycling and conservation

•

economic considerations in the chemical industry, such as the availability and cost of raw materials and .. energy

•

the importance of chemicals in both industry and everyday life.

Specific content has been limited in order to encourage this approach, and to allow flexibility in the design of teaching programmes. CIE provides schemes of work, which can be found on the CIETeacher Support website. Candidates may follow the Core curriculum only or they may follow the Extended curriculum, which includes both the Core and the Supplement.

Core

Supplement

•

Describe the states of matter and explain their interconversion in terms of the kinetic particle theory

•

•

Describe and explain diffusion

•

Describe evidence for the movement of particles in gases and liquids (a treatment of Brownian motion is not required)

Describe dependence of ra
2.1 Measurement Core •

Name appropriate apparatus for the measurement of time, temperature, mass and volume, including burettes, pipettes and measuring cylinders

2.2 (a) Criteria of purity Core

Supplement

•

Describe paper chromatography

•

•

Interpret simple chromatograms

Interpret simple chromatograms, including the use of R, values

•

Identify substances and assess their purity from melting point and boiling point information

•

•

Understand the importance of purity in substances in everyday life, e.g. foodstuffs and drugs

Outline how chromatography techniques can be applied to colourless substances by exposing chromatograms to substances called locating agents (knowledge of specific locating agents is not required)

12

2.2 (b) Methods of purification Core

•

Describe methods of purification by the use of a suitable solvent. filtration. crystallisation, distillation (including use of fractionating column). (Refer to the fractional distillation of crude oil in sectioo 14.2 flnd products of fermentation in section 14.6.)

•

Suggest suitable purification techniques, given information about the substances involved

3.1 Atomic structure and the Periodic Table Core

•

State the relative charges and approximate relative masses of protons. neutrons and electrons

•

Define proton number and nucleon number

•

Use proton number and the simple structure of atoms to explain the basis of the Periodic Table (see section 9), with special reference to the elements of proton number 1 to 20

•

Define isotopes

•

State the two types of isotopes as being radioactive and non-radioactive

•

State one medical and one industrial use of radioactive isotopes

•

Describe the build-up of electrons in 'shells' and understand the significance of the noble gas electronic structures and of valency electrons (the ideas of the distribution of electrons in s and p orbitals and in d block elements are not required.) Note: a copy of the Periodic Table. as shown in the Appendix, will be available in Papers 1, 2 and 3)

13

3.2 Bonding: the structure of matter Core

•

Describe the differences between elements . mixtures and compounds, and between metals and non-metals

•

Describe an alloy, such as brass, as a mixture of metal with other elements

a-

3.2 (a) Ions and ionic bonds Core

• •

Describe the formation of ions by electron loss or gain Describe the formation of ionic bonds between elements from Groups I and VII

3.2 (b) lvlolecules and covalent bonds Core

Supple.ment

•

Describe the formation of single covalent bonds in H,. C~ . H,O, CH, and HC1 as the sharing of pairs of electrons leading to the noble gas configuration

•

Describe the formation of ionic bonds between metallic and non-metallic elements

•

Describe the differences in volatility, solubility and electrical conductivity between ionic and covalent compounds

•

Describe the lattice structure of ionic compounds as a regular arrangement of alternating positive and negative ions

3.2 (c) lvlacromolecules Core

Supplement

•

Describe the giant covalent structures of graphite and diamond

•

•

Relate their structures to the use of graphite as a lubricant and of diamond in cutting

Describe the electron arrangement in more complex covalent molecules such as N 2, C,H,. CH,OH and CO,

•

Describe the macromolecular structure of silicon(JV) oxide (silicon dioxide)

3.2 (d) lvletallic bonding

Supplement

----------·---- ·-------------------

14

•

Describe the similarity in properties between diamond and silicon(IV) oxide. related to their structures

•

Describe metallic bonding as a lattice of positive ions in a 'sea of electrons' and use this to describe the electrical conductivity and malleability of metals

--~--~--------------

Core

Supplement

•

Use the symbols of the elements and write the formulae of simple compounds

•

•

Deduce the formula of a simple compound from the relative numbers of atoms present

Determine the formula of an ionic compound from the charges on the ions .. present

•

Deduce the formula of a simple compound from a model or a diagrammatic representation

Construct equations with state symbols, including ionic equations

•

Deduce the balanced equation for a chemical reaction, given relevant information

• •

Construct word equations and simple balanced chemical equations

•

Define relative atomic mass, A,

•

Define relative molecular mass, M,, as the sum of the relative atomic masses (relative formula mass or M, will be used for ionic compounds) (Calculations involving reacting masses in simple proportions may be set. Calculations will not involve the mole concept.)

4.1 The mole concept

Supplement •

Define the mole and the Avogadro

constant

15

•

Use the molar gas volume, taken as 24 dm 3 at room temperature and pressure

•

Calculate stoichiometric reacting masses and volumes of gases and solutions, solution concentrations expressed in g/dm' and mol/dm'. (Calculations involving the idea of limiting reactants may be set. Questions on the gas laws and the conversion of gaseous volumes to different temperatures and pressures will not be set.)

•

Calculate empirical formulae and molecular formulae

•

Calculate % yield and % purity

Core

Supplement

•

•

Relate the products of electrolysis to the electrolyte and electrodes used, exempJified by the specific examples in the Core together with aqueous copper(ll) sulfate using carbon electrodes and using copper electrodes (as used in the refining of copper)

Describe the electrode products in the electrolysis of: molten lead(! I) bromide concentrated hydrochloric acid concentrated aqueous sodium chloride between inert electrodes (platinum or carbon)

•

State the general principle that metals or hydrogen are formed at the negative electrode (cathode). and that non-metals (other than hydrogen) are formed at the positive electrode (anode)

•

Describe electrolysis in terms of the ions present and reactions at the electrodes in the examples given

•

Predict the products of the electrolysis of a specified binary compound in the molten state

•

•

Describe the electroplating of metals

Predict the products of electrolysis of a specified halide in dilute or concentrated aqueous solution

•

Name the uses of electroplating

•

Describe, in outline, the manufacture of

•

Describe the reasons for the use of copper and (steel-cored) aluminium in cables, and why plastics and ceramics are used as insulators

aluminium from pure aluminium oxide in molten cryolite chlorine and sodium hydroxide from concentrated aqueous sodium chloride (Starting materials and essential conditions should be given but not technical details or diagrams.)

-

6. 1 Energetics of a reaction Core

•

Supplement

Describe the meaning of exothermic and

•

endothermic reactions

16

Describe bond breaking as endothermic and bond forming as exothermic

6.2 Production of energy Core

Supplement •

Describe the production of electrical energy from simple cells, i.e. two electrodes in an electrolyte. (This should be linked with tbe·reactivity series in section 10.2 and redox in section 7.3.)

•

Describe the use of hydrogen as a potential fuel reacting with oxygen to generate electricity in a fuel cell (details of the construction and operation of a fuel cell are not required)

Describe the production of heat energy by burning fuels •

Describe hydrogen as a fuel

o

Describe radioactive isotopes, such as source of energy

235

U, as a

7.1 Speed of reaction Core

Supplement

•

Describe the effect of concentration, particle size, catalysts (including enzymes) and temperature on the speeds of reactions

•

Devise a suitable method for investigating the effect of a given variable on the speed of a reaction

•

Describe a practical method for investigating the speed of a reaction involving gas evolution

•

Interpret data obtained from experiments concerned with speed of reaction

•

Describe the application of the above factors to the danger of explosive combustion with fine powders (e.g. flour mills) and gases (e.g. mines)

•

17

Describe and explain the effects of temperature and concentration in terms of

collisions between reacting particles •

Describe the effect of light on the speed of reactions

•

Describe the use of silver salts in photography as a process of reduction of silver ions to silver; and photosynthesis as the reaction between carbon dioxide and water in the presence of chlorophyll and sunlight (energy) to produce glucose

' 7.2 Reversible reactions Core

Supplement

•

•

Describe the idea that some chemical reactions can be reversed by changing the reaction conditions

Predict the effect of changing the conditions (temperature and pressure) on other reversible reactions

(Limited to the effects of heat on hydrated salts. Concept of equilibrium is not required.)

•

Concept of equilibrium-

7.3 Redox

Supplement

Core Define oxidation and reduction in terms of oxygen

•

•

loss/gain. (Oxidation state limited to its use to name ions, e.g. iron(! I), iron(III), copper([]), manganate(VIl), dichromate(Vl) .)

Define redox in terms of electron transfer

•

Identify redox reactions by changes in oxidation state and by the colour changes involved when using acidified potassium manganate(VIl), and potassium iodide. (Recall of equations involving KMnO, is not required.)

8.1 The characteristic properties of acids and bases Core

Supplement

•

•

Describe the characteristic properties of acids as reactions with metals, bases, carbonates and effect

proton transfer, limited to aqueous solutions

on litmus •

Describe the characteristic properties of bases as

Define ac1ds and bases in terms of

•

reactions with acids and with ammonium salts and

Describe the meaning of weak and strong acids and bases

effect on litmus •

Describe neutrality and relative acidity and alkalinity in terms of pH (whole numbers only) measured using Universal Indicator paper

•

Describe and explain the importance of controlling acidity in soil

8.2 Types of oxides Core

Supplement

•

•

Classify oxides as either acidic or basic, related to

Further classify other oxides as neutral or amphoteric

metallic and non-metallic character

18

8.3 Preparation of salts Core

Supplement

•

•

Describe the preparation of insoluble salts by precipitation

•

Suggest a method of making a given salt from suitable starting material. given appropriate information

Describe the preparation, separation and purification of salts as examples of some of the techniques specified in section 2.2(b) and the reactions specified in section 8.1

8.4 Identification of ions and gases Core

•

Describe the following tests to identify:

aqueous cations: aluminium. ammonium. calcium, copper(!!), iron(fl), iron(lll) and zinc (using aqueous sodium hydroxide and aqueous ammonia as appropriate) (Formulae of complex ions are not required.)

anions: carbonate (by reaction with dilute acid and then limewater). chloride (by reaction under acidic conditions with aqueous silver nitrate), iodide (by reaction under acidic conditions with aqueous silver nitrate), nitrate (by reduction with aluminium), sulfate (by reaction under acidic conditions with aqueous barium ions) gases:

ammonia (using damp red litmus paper), carbon dioxide (using limewater), chlorine (using damp litmus paper), hydrogen (using lighted splint). oxygen (using a glowing splint).

19

Core

•

Describe the Periodic Table as a method of classifying elements and its use to predict properties of elements

9.1 Periodic trends Core

Supplement

•

•

Describe the change from metallic to non-metallic character across a period

Describe the relationship between Group number, number of valency electrons and metallic/non-metallic character

9.2 Group properties Supplement

Core

•

Describe lithium, sodium and potassium in Group I as a collection of relatively soft metals showing a trend in melting point, density and reaction with water

•

Predict the properties of other elements in Group I, given data, where appropriate

•

Describe chlorine, bromine and iodine in Group VII as a collection of diatomic non-metals showing a trend in colour, and state their reaction with other halide ions Predict the properties of other elements in Group VII, given data where appropriate

•

Identify trends in other Groups, given information about the elements concerned

9.3 Transition elements Core •

Describe the transition elements as a collection of metals having high densities, high melting points and forming coloured compounds, and which, as elements and compounds, often act as catalysts

fi.4 Noble gases Core •

Describe the noble gases as being unreactive Describe the uses of the noble gases in providing an inert atmosphere, i.e. argon in lamps, helium for filling balloons

---~·------

20

10.1 Properties of metals Core

Describe the general physical and chemical properties of metals Explain why metals are often used in the form of alloys Identify representations of alloys from diagrams of structure

•

10.2. Reactivity series Core

Supplement

Place in order of reactivity: potassium, sodium, calcium, magnesium, zinc, iron, (hydrogen) and copper, by reference to the reactions, if any, of the metals with

•

water or steam

Describe the reactivity series as related to the tendency of a metal to form its positive ion, illustrated by its reaction, if any, with the aqueous ions

dilute hydrochloric acid

the oxides

and the reduction of their oxides with carbon

of the other listed metals

•

•

Describe the action of heat on the hydroxides and nitrates of the listed metals

•

Account for the apparent unreactivity of aluminium in terms of the oxide layer which adheres to the metal

Deduce an order of reactivity from a given set of experimental results

10.3 (a) Extraction of metals Core

Supplement

•

Describe the ease in obtaining metals from their ores by relating the elements to the reactivity series

•

•

Name the main ore of aluminium as bauxite (see section 5) Describe the essential reactions in the extraction of iron from hematite

•

Describe the conversion of iron into steel using basic oxides and oxygen

21

describe in outline, the extraction of zinc from zinc blende

10.3 (b) Uses of metals Core

Supplement

•

•

Name the uses of aluminium: in the manufacture of aircraft because of its strength

and for making brass

and low density

•

in food containers because of its resistance to corrosion •

Describe the idea of changing the properties of iron by the controlled use of additives to form steel alloys

•

Name the uses of mild steel (car bodies and machinery) and stainless steel (chemical plant and cutlery)

Name the uses of zinc for galvanising Name the uses of copper related to its properties (electrical wiring and in cooking utensils)

Supplement

Core

•

Describe a chemical test for water

•

Describe, in outline, the purification of the water supply in terms of filtration and chlorination

•

Name some of the uses of water in industry and in the home

•

Describe'the composition of clean air as being approximately 79% nitrogen, 20% oxygen and the remainder as being a mixture of noble gases, water vapour and carbon dioxide

•

Name the common pollutants in the air as being carbon monoxide, sulfur dioxide, oxides of nitrogen and lead compounds

•

State the source of each of these pollutants: carbon monoxide from the incomplete combustion of carbon-containing substances sulfur dioxide from the combustion of fossil fuels which contain sulfur compounds (leading to 'acid rain'- see section 13) oxides of nitrogen from car exhausts

•

•

Describe and explain the presence of oxides of nitrogen in car exhausts and their catalytic removal

•

Describe the separation of oxygen and nitrogen from liquid air by fractional

State the adverse effect of common pollutants on buildings and on health

distillation

22

•

Describe methods of rust prevention, specifically paint and other coatings to exclude oxygen

•

Describe the need for nitrogen-, phosphorus- and potassium-containing fertilisers

•

Describe the displacement of ammonia from its salts

•

State that carbon dioxide and methane are greenhouse gases and may contribute to climate change

•

Describe the formation of carbon dioxide:

•

Describe sacrificial protection in terms of the reactivity series of metals and galvanising as a method of rust prevention

•

Describe the essential conditions for the manufacture of ammonia by the Haber process including the sources of the hydrogen and nitrogen, i.e. hydrocarbons or steam and air

•

Describe the carbon cycle, in simple terms, to include the processes of combustion, respiration and photosynthesis

as a product of complete combustion of carboncontaining substances as a product of respiration as a product of the reaction between an acid and a carbonate •

State the sources of methane, including decomposition of vegetation and waste gases from digestion in animals

Supplement

23

•

Name some sources of sulfur

•

Name the use of sulfur in the manufacture of sulfuric acid

•

Name the uses of sulfur dioxide as a bleach in the manufacture of wood pulp for paper and as a food preservative (by killing bacteria)

•

Describe the manufacture of sulfuric acid by the Contact process, including essential conditions

•

Describe the properties of dilute sulfuric acid as a typical acid

Core

•

Describe the manufacture of lime (calcium oxide) from calcium carbonate (limestone) in terms of the chemical reactions involved

•

Name some uses of lime and slaked lime as in treating acidic soil and neutral ising acidic industrial waste products, e.g. flue gas desulfurisation

•

Name the uses of calcium carbonate in the manufacture of iron and of cement

14.1 Names of compounds Supplement

Core

•

Name and draw the structures of methane, ethane, ethanol, ethanoic acid and the products of the reactions stated in sections 14.4-14.6

•

State the type of compound present. given a chemical name ending in -ane. -ene, -ol, or -oic acid, or a molecular structure

14.2 Fuels Core •

Name the fuels coal, natural gas and petroleum Name methane as the main constituent of natural gas

•

Describe petroleum as a mixture of hydrocarbons and its separation into useful fractions by fractional distillation Name the uses of the fractions as: refinery gas for bottled gas for heating and cooking gasoline fraction for fuel (petrol) in cars naphtha fraction for making chemicals kerosene/paraffin fraction for jet fuel diesel oil/gas oil for fuel in diesel engines fuel oil fraction for fuel for ships and home heating systems lubricating fraction for lubricants, waxes and polishes bitumen for making roads

24

Name and draw the structures of the unbranched alkanes. alkenes (not cistrans), alcohols and acids containing up to four carbon atoms per molecule

14.3 Homologous series Core

Supplement

•

•

Describe the general characteristics of an homologous series

•

Describe and identify structural

Describe the concept of homologous series as a 'family' of similar compounds with similar properties due to the presence of the same functional group

isomerism

14.4 Alkanes Core

Supplement

•

Describe the properties of alkanes (exemplified by methane) as being generally unreactive, except in terms of burning

•

•

Describe the bonding in alkanes

Describe substitution reactions of alkanes with chlorine

14.5 Alkenes Core

Supplement

•

Describe the manufacture of alkenes and of hydrogen by cracking

•

•

Distinguish between saturated and unsaturated hydrocarbons

•

-

from molecular structures

-

by reaction with aqueous bromine

Describe the formation of poly(ethene) as an example of addition polymerisation of monomer units

14.6 Alcohols Core

•

Describe the formation of ethanol by fermentation and by the catalytic addition of steam to ethene

•

Describe the properties of ethanol in terms of burning

•

Name the uses of ethanol as a solvent and as a fuel

25

Describe the properties of alkenes in terms of addition reactions with bromine, hydrogen and steam

14.7 Acids

14.8 Macromolecules

Supplement •

Describe the formation of ethanoic acid by the oxidation of ethanol by fermentation and with acidified potassium manganate(VII)

•

Describe ethanoic acid as a typical weak acid

•

Describe the reaction of ethanoic acid with ethanol to give an ester (ethyl ethanoatel

Supplement •

14.8 (al Synthetic polymers

.,

Describe macromolecules in terms of large molecules built up from small units (mononomers), different macromolecules having different units and/or different linkages

Supplement •

Name some typical uses of plastics and of man-made fibres

•

Describe the pollution problems caused by non-biodegradable plastics

•

Deduce the structure of the polymer product from a given alkene and vice versa

•

Describe the formation of nylon (a polyamide) and Terylene (a polyester) by condensation polymerisation, the structure of nylon being represented as: 0

I .

0

0

I

0

I

0

I

I

-c~c-~-[]-~-c~c-~-[]-~-c~ H

H

H

H

and the structure of Terylene as: 0

0

0

0

-~~~-o-[]-o-~~~-o-[]-o(Details of manufacture and mechanisms of these polymerisations are not required.)

26

14.8 (b) Natural macromolecules

Supplement •

Name proteins, fats and carbohydrates as the main constituents of food

•

Describe proteins as possessing the same (amide) linkages as nylon but with different units Describe the structure of proteins as: H

0

R

H

0

I I I I I -N-C-C-N-C-C-N-C-C1 I I I R H 0 R •

Describe the hydrolysis of proteins to amino acids (Structures and names are not required.)

•

Describe fats as esters possessing the same linkage as Tery!ene but with different units

•

Describe soap as a product of hydrolysis of fats

•

Describe complex carbohydrates in terms of a large number of sugar units, considered as Ho-D-oH, joined together by condensation polymerisation, e.g.

-·--~-

-o-D-o-D-o-D-o-

•

Describe the acid hydrolysis of complex carbohydrates (e.g. starch) to give simple sugars

•

Describe the fermentation of simple sugars to produce ethanol (and carbon dioxide) (Candidates will not be expected to give the molecular formulae of sugars.)

•

Describe, in outline, the usefulness of chromatography in separating and identifying the product of hydrolysis of carbohydrates and proteins

-----~

27

6.1 Grade descriptions

;

I

The scheme of assessment is intended to encourage positive achievement by all candidates.

•

relate facts to principles and theories and vice versa

•

state why particular techniques are preferred for a procedure or operation

•

select and collate information from a number of sources and present it in a clear logical form

•

solve problems in situations which may involve a wide range of variables

•

process data from a number of sources to identify any patterns or trends

•

generate a hypothesis to explain facts, or find facts to support a hypothesis

•

link facts to situations not specified in the syllabus

•

describe the correct procedure(s) for a multi-stage operation

•

select a range of information frorn a given source and present it in a clear logical form

•

identify patterns or trends in given information

•

solve a problem involving more than one step, but with a limited range of variables

•

generate a hypothesis to explain a given set of facts or data

•

recall facts contained in the syllabus

•

indicate the correct procedure for a single operation

•

select and present a single piece of information from a given source

•

solve a problem involving one step, or more than one step if structured help is given

•

identify a pattern or trend where only minor manipulation of data is needed

•

recognise which of two given hypotheses explains a set of facts or data

A Grade A candidate will be able to:

A Grade C candidate will be able to:

A Grade F candidate will be able

to:

36

6.1 Grade descriptions The scheme of assessment is intended to encourage positive achievement by all candidates.

•

relate facts to principles and theories and vice versa

•

state why particular techniques are preferred for a procedure or operation

•

select and collate information from a number of sources and present it in a clear logical form

o

solve problems in situations which may involve a wide range of variables

•

process data from a number of sources to identify any patterns or trends

o

generate a hypothesis to explain facts, or find facts to support a hypothesis

• • •

link facts to situations not specified in the syllabus

A Grade A candidate will be able to:

., A Grade C candidate will be able to:

A Grade F candidate will be able to:

describe the correct procedure(s) for a multi-stage operation select a range of information from a given source and present it in a clear logical form

•

identify patterns or trends in given information

•

solve a problem involving more than one step, but with a limited range of variables

•

generate a hypothesis to explain a given set of facts or data

• • • •

recall facts contained in the syllabus

• •

indicate the correct procedure for a single operation select and present a single piece of information from a given source solve a problem involving one step, or more than one step if structured help is given identify a pattern or trend where only minor manipulation of data is needed recognise which of two given hypotheses explains a set of facts or data

~-~-------·--·--~----------~-----------

36

---

6.3 Notes for use in qualitative analysis Tests for anions

carbonate (C0 3''1

add dilute acid

effervescence, carbon dioxide produced

chloride (CrJ (in solution}

acidify with dilute nitric acid, then add aqueous silver nitrate

white ppt.

iodide WI lin solution}


yellow ppt.

nitrate (N0 3·1 [in solution}

add aqueous sodium hydroxide, then aluminium foil; warm carefully

ammonia produced

sulfate (SO ,'·1 [in solution}

acidify, then add aqueous barium nitrate

white ppt.

Tests for aqueous cations

aluminium IAZ'•I

white ppt., soluble in excess giving a colourless solution

ammonium (NH;J

ammonia produced on warming

calcium (Ca''l

white ppt., insoluble in excess

no ppt. or very slight white ppt.

light blue ppt., insoluble in excess

light blue ppt., solub[e in excess, giving a dark blue solution

green ppt., insoluble in excess


red-brown ppt., insoluble in excess


white ppt., soluble in excess, giving a colourless solution


ammonia (NH 3)

turns damp red litmus paper blue

carbon dioxide (C0 2)

turns limewater milky

chlorine (CI,)

bleaches damp litmus paper

hydrogen

'pops' with a lighted splint

oxygen 10,1

relights a glowing splint

38


6.4 Safety in the laboratory Responsibility for safety matters rests with Centres. Further information can be found in the following UK associations. websites, publications and regulations.

Associations CLEAPSS is an advisory service providing support in practical science and technology, primarily for UK schools. International schools and post-16 colleges can apply for associate membership which includes access to the CLEAPSS publications listed below http:/ /www.cleapss.org.uk

Websites http:/ /www.chemsoc.org/networks/learnnet/Safety.htm http://www. ncbe.reading.ac.uk/NCBE/SAFETYI menu.html http:/ /www.microbiologyonline.org.uk/safety.html

Publications Safeguards in the School Laboratory, ASE, 11
Ul< Regulations Control of Substances Hazardous to Health Regulations (COSH H) 2002 http:/ /www.opsi.gov.uk/SI/si2002/20022677.htm, a brief guide may be found at http:/ /www.hse.gov.uk{pubns/indg136.pdf

39

6.5 Glossary of terms used in science papers The glossary (which is relevant only to Science subjects) will prove helpful to candidates as a guide. but it is neither exhaustive nor definitive. The glossary has been deliberately kept brief, not only with respect to the number of terms included, but also to the descriptions of their meanings. Candidates should appreciate that the meaning of a term must depend, in part, on its context. 1.

Define (the term(s) ... I is intended literally, only a formal statement or equivalent paraphrase being required.

2.

What do you understand by/What is meant by (the term lsi .. I normally implies that a definition should be given, together with some relevant comment on the significance or context of the term(s) concerned, especially where two or more terms are included in the question. The amount of supplementary comment intended should be interpreted in the light of the indicated mark value.

3.

State implies a concise answer with little or no supporting argument (e.g. a numerical answer that can readily be obtained 'by inspection').

4.

List requires a number of points, generally each of one word, with no elaboration. Where a given number of points is specified this should not be exceeded.

5.

Explain may imply reasoning or some reference to theory, depending on the context.

6.

Describe requires the candidate to state in words (using diagrams where appropriate) the main points of the topic. It is often used with reference either to particular phenomena or to particular experiments. In the former instance, the term usually implies that the answer should include reference to (visual) observations associated with the phenomena. In other contexts, describe should be interpreted more generally (i.e. the candidate has greater discretion about the nature and the organisation of the material to be included in the answer). Describe and explain may be coupled, as may state and explain.

7.

Discuss requires the candidate to give a critical account of the points involved in the topic.

8.

Outline implies brevity (i.e. restricting the answer to giving essentials).

9.

Predict implies that the candidate is not expected to produce the required answer by recall but by making a logical connection between other pieces of information. Such information may be wholly given in the question or may depend on answers extracted in an earlier part of the question. Predict also implies a concise answer with no supporting statement required.

10. Deduce is used in a similar way to predict except that some supporting statement is required, e.g. reference to a law or principle, or the necessary reasoning is to be included in the answer. 11. Suggest is used in two main contexts, i.e. either to imply that there is no unique answer (e.g. in Chemistry, two or more substances may satisfy the given conditions describing an 'unknown'), or to imply that candidates are expected to apply their general knowledge of the subject to a 'novel' situation, one that may be formally 'not in the syllabus'- rnany data response and problem solving questions are of this type. 12. Find is a general term that may variously be interpreted as calculate, measure, determine, etc.

40

13. Calculate is used when a numerical answer is required. In general, working should be shown, especially where two or more steps are involved. 14. Measure implies that the quantity concerned can be directly obtained from a suitable measuring instrument (e.g. length, using a rule, or mass, using a balance). 15. Determine often implies that the quantity concerned cannot be measured directly but is obtained by, calculation, substituting measured or known values of other quantities into a standard formula e.g. relative molecular mass.

·-

16. Estimate implies a reasoned order of magnitude statement or calculation of the quantity concerned, making such simplifying assumptions as may be necessary about points of principle and about the values of quantities not otherwise included in the question. 17. Sketch. when applied to graph work, implies that the shape and/or position of the curve need only be qualitatively correct, but candidates should be aware that, depending on the context. some quantitative aspects may be looked for (e.g. passing through the origin, having an intercept). In diagrams, sketch implies that simple, freehand drawing is acceptable; nevertheless, care should be taken over proportions and the clear exposition of important details.

41

6.6 Mathematical requirements Calculators may be used in all parts of the examination. Candidates should be able to:

• • • •

add .._subtract, multiply and divide use averages, decimals, fractions, percentages, ratios and reciprocals recognise and use standard notation use direct and inverse proportion

•

use positive, whole number indices

• •

draw charts and graphs from given data interpret charts and graphs

•

select suitable scales and axes for graphs

• •

make approximate evaluations of numerical expressions recognise and use the relationship between length, surface area and volume and their units on metric scales

•

use usual mathematical instruments (ruler, compasses, protractor, set square)

•

understand the meaning of angle, curve, circle, radius, diameter, square, parallelogram, rectangle and diagonal

•

solve equations of the form x = yz for any one term when the other two are known.

42

.J

'

'

The Periodic Table of the Elements Group I

II

I

I

Ill

I

IV

I

v

I

VI

I

VII

I

0

1

4

H

He Heiiun1

Hydrogen

1 7

9

11

Li

Be

B

Beryllrum

Lrthrunl

3

,.

2

Boron

4

12

14

16

19

20

c

N

0

F

Ne

Nrtrogen

Carbon

'G·

5

7

Oxvgcn

8

No~

fluonnu

10

9

23

24

27

28

31

32

35.5

40

Na

Mg

A/

Si

p

s

C/

Ar

Aluminium

Srflcon

Sod rum

lvld(l
11

12

13

"

39

Ca

K

C~ICrum

Potassrum

19

45

48

51

52

55

56

59

59

64

65

70

Sc

Ti

v

Cr

Mn

Fe

Co

Ni

Cu

Zn

Ga

Scandium

20

Titamum

22

21

Vanadrurn

23

Chromium

24

85

88

89

91

93

96

Rb

Sr

y

Zr

Nb

Mo

Rubrdium

37

Yttrium

Strontium

38

Zircomum

39

Nrobium

41

40

Iron

Manganese

26

25

Tc

Molybdenum Technetium 42 43

I,Jrc~el

Cobalt

28

27

Z•nc

Copper

29

Gallrurll

31

30

101

103

106

108

112

115

Ru

Rh

Pd

Ag

Cd

In

Ruthenium 44 190

Rhodium

45

Palladium

46

Silver

Cadmium

48

47

"

Sulfur

16

Argcn

Chlounc

18

17

73

75

79

80

84

Ge

As

Se

Br

Kr

Gerrnar.,um 32 119

Arsemc

33

Krypton

36

35

122

128

127

131

Sb

Te

I

Xe

Antimony

';;n

51

50

Bromme

Selenli.Bll

34

Sn

tndrun1

49

Phosphorus

15

Xenon

lod'na

Teilunum

52

54

53

133

137

139

178

181

184

186

192

195

197

201

204

207

Cs

Ba

La

Hf

Ta

w

Re

Os

lr

Pt

Au

Hg

Tl

Pb

Bi

Po

At

Rn

c~esrum

Barium

Lanthanum

Hafnium

Tantalum

Tun(!sten

Rhenium

Osm•um

l
Plahnum

Gold

Mercury

Thallium

Lead

B•smulh

Polon•um

A.stat"'~

Radl>'1

-7

56

55

Fr fronc•um

87

·ss-71

72

226

227

Ra

Ac

Rad•um

73

76

75

74

78

77

79

80

81

209

83

82

"

c

86

85

actm•um

88

89

t

Lanthanoid series

t90-1 03 Actinoid series

Key0

140

141

144

Ce

Pr

Nd

Cerium

PraseO
58

a = relat1vei.l tomic rn<.lss

X= atomic symbol b =proton (atomic) number 90

Neodymium

60

59 232

Pm Prometh•um

150

152

157

159

163

165

167

169

173

175

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Samanum

62

61

Europ•um

63

Tmb
GadolllliUm

64

65

Dysp
66

Hoi mourn

Erb1um

68

67

Thuhum

Luleuum

Yumbium

71

70

69

238

Th

Pa

u

Np

Pu

Am

Cm

Bl<

Cf

Es

Fm

Md

No

Lr

Thorium

PrO!OCII!liUffi

Uran•um

Neptumum

PlutOnium

Ameut•um

Cunum

Berkelium

Cal•fornoum

E•nsteu11um

Ferm1um

Mendelov1um

~lobelium

Lawrencoum

91

92

93

94

95

96

97

98

99

The volume of one mole of any gas is 24 dm 3 at room temperature and pressure {r.t.p.)

~

101

102

---'--

103

CHEMISTRY 0620 IGC0to ZUlu

NOTES FOR USE IN QUALITATIVE ANALYSIS Tests for anions anion

test

test result

carbonate (CO 3 '-)

add dilute acid

effervescence, carbon dioxide produced

chloride (CZ-) [in solution]

acidify with dilute nitric acid, then add aqueous silve~ nitrate

white ppt.

iodide (J) [in solution]


yellow ppt.

nitrate (NO,l [in solution]

add aqueous sodium hydroxide, then aluminium foil; warm carefully

ammonia produced

sulfate (SO/l [in solution]

~cidify,

white ppt.

then add aqueous barium nitrate

Tests for aqueous cations cation

effect of aqueous sodium hydroxide

effect of aqueous ammonia

aluminium (A1 3')

white ppt., soluble in excess giving a colourless solution


ammonium (NH;)

ammonia produced on warming

calcium (Ca2 ')


no ppt. or very slight white ppt.

copper (Cu'•)

light blue ppt., insoluble in excess

light blue ppt., soluble in excess, giving a dark blue solution



iron(I!I) (Fe 3•)



zinc (Zn'•)



iron(II) (Fe

2

')

-

Tests for gases gas

test and test result

ammonia (NH3 )

turns damp red litmus paper blue

carbon dioxide (C0 2 )

turns limewater milky

chlorine ( C 12 )

bleaches damp litmus paper

hydrogen (Hz)

'pops' with a lighted splint

oxygen (0 2 )

relights a glowing splint

IG Chemsitry Papers

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