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2015 O’LEVEL SCIENCE CHEMISTRY 5078/03 SECTION A 1.
Describe briefl� the method and the res�lts �o� �o�ld e�pect in disting�ishing bet�een (a)
a sol�tion of pH 1 and the other pH 14, method
[1]
Add a fe� drops of Uni�ersal Uni�ersal Indicato Indicator Indicator. r
res�lt for sol�tion of pH 1
Indicator t�rns from green to red.
res�lt for sol�tion of pH 14 Indicator t�rns from green to �iolet. [Allo� omission of green. Allo� litm�s paper �ith �ith correct correct colo�r colo�r indicated.] indicated.] (b)
ethane and ethene gases, method
(c)
B�bble gas into aq�eo�s bromine bromine in the t he dark.
res�lt for ethene
Red�bro�n bromine sol�tion t�rns colo�rless.
res�lt for ethane
Red�bro�n bromine sol�tion remains �nchanged.
an endothermic and e�othermic reaction, method
(d)
[1]
[1]
Place a thermomete thermometerr into the reaction mi�t�re.
res�lt for endothermic
Thermometer reading dropped.
res�lt for e�othermic
Thermometer reading rose.
a sodi�m chloride and sodi�m s�lfate sol�tion. method
[1]
Add a fe� drops of acidified sol�tion. acidified bari�m nitrate nit rate sol�tion sol�tion
res�lt for sodi�m chloride
Sol�tion remains colo�rless.
res�lt for sodi�m s�lfate A �hite precipitate forms in sol�tion. [Accept acidified lead(II) nitrate/ sil�er nitrate sol�tion �ith correct res�lt.]
2.
S�bstances are often classified into one of the fi�e gro�ps gi�en belo�. gro�p element compo�nd mi�t�re of elements mi�t�re of compo�nds mi�t�re of elements and compo�nds
Letter A B C D E
Fill in a letter, A to E, E, for each of the substances below that best classify them. air
E
brass
C
h�drogen
A
sodi�m carbonate
B
[2]
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3.
(a)
Complete the table b� filling in the blank bo�es. relati�e mass
relati�e charge
proton
1
1+
ne�tron
1
0
1
electron
(b)
(i)
(ii)
[3]
1
140
A ber�lli�m ion can be represented as Be . State the n�mber of each s�batomic particle in the ion. Protons
4
Ne�trons
5
Electrons
2
[3]
Write an ionic eq�ation for the formation of this ion from its atom.
[2]
Be Be + 2e [1mark for missing electrons] electrons]
4.
Atoms of non�metallic elements can combine �ith other atoms to form man� different compo�nds. (a)
One s�ch compo�nd is ammonia. It is a non�cond�ctor of electricit� and has a lo� melting point. (i)
Name the t�pe of chemical bonding in ammonia.
[1]
Covalent bonding. (ii)
Dra� a �dot�and�cross� diagram to sho� the arrangement of electrons in a molec�le of ammonia.
H
N
H
Key : - electron of H - electron of N
H [All shells m�st dra�n. Note that si�e of H� H �atom is smaller than N�atom] [Ke� is optional]
[2]
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(b)
Another of these compo�nds, magnesi�m chloride, has a high melting point and is a cond�ctor of electricit� �hen molten. (i)
Name the t�pe of chemical bonding present in magnesi�m chloride.
[1]
Ionic bonding. (ii)
5.
Dra� a �dot�and�cross� diagram of the arrangement of electrons in magnesi�m chloride.
[2]
Sodi�m h�drogencarbonate and sodi�m carbonate ha�e similar chemical properties. The former can be made in the laborator� b� b�bbling carbon dio�ide thro�gh a cold, concentrated sol�tion of sodi�m carbonate. Na CO + CO + H O 2NaHCO (a)
The sodi�m carbonate sol�tion has a concentration of 2.0 mol/dm . What �ol�me of this sol�tion contains 500g of sodi�m carbonate? No. of moles of sodi�m carbonate =
[2]
()()
= 4.7169 mol Vol�me of sol�tion =
. .
= 2.355 = 2.36 () (b)
Calc�late the ma�im�m mass of sodi�m h�drogencarbonate that can be made from 500g of sodi�m carbonate.
[2]
From eq�ation, ratio moles
Na CO 1 4.7169
: :
NaHCO 2 9.43396 mol
Ma�im�m mass of NaHCO = 9.43396 (23+1+12+163) = 792 g (3) (3 ) (c)
Baking po�der consists mainl� of sodi�m h�drogencarbonate and a small q�antit� of an acidic s�bstance. When in contact �ith moist�re, the acidic s�bstance reacts �ith the h�drogencarbonate. S�ggest �h� moist bread do�gh, containing baking po�der, �ill rise �hen placed in a hot o�en.
During reaction, carbon dioxide gas is produced and expanded in the high temperature causing more space to be taken up, up resulting in the rise of dough.
[1]
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6. dil�te nitric acid ne�tralise �ith metal o�ide C
ne�tralise �ith metal o�ide E
distillation B bl�e sol�tion
bro�n sol�tion
precipitate �sing aq�eo�s sodi�m h�dro�ide
F colo�rless distillate
A light bl�e precipitate (a)
precipitate �sing aq�eo�s sodi�m h�dro�ide
D red�bro�n precipitate
S�ggest the identit� of these s�bstances. A
Copper(II) h�dro�ide
B
Copper(II) nitrate
C
Copper(II) o�ide
D
Iron(III) h�dro�ide
E
Iron(III) o�ide
F
P�re �ater
[6]
[Chemical form�lae accepted. Water for F accepted.] (b)
Write a balanced chemical eq�ation for an� one of the reactions abo�e. An� one :
[2]
C�(NO ) + 2NaOH C�(OH) + 2NaNO C�O +2HNO C�(NO ) + H O Fe(NO ) + 3NaOH Fe(OH) + 3NaNO Fe O + 6HNO 2Fe(NO ) + 3H O
7.
(a)
Write the chemical form�la for propane and calc�late its relati�e molec�lar mass. form�la form�la
relati�e molec�las mass =
(3 (3 ) + ( ) =4
[2]
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(b)
(i)
Calc�late the �ol�me of 10g of ethane at room temperat�re and press�re. No. of moles of ethane
=
[2]
()
= 0.33333 mol Vol�me of ethane = 0.33333 24dm = .00 ()
(ii)
Ethane comb�sts completel� as sho�n b� the eq�ation belo�. 2C H + 7O 4CO + 6H O Calc�late the �ol�me of o��gen needed to b�rn 10g of ethane completel�. Using moles of 10g of ethane f rom (i), C H ratio 2 : moles 0.33333 :
[1]
O 4 0.66666 mol
Vol�me of o��gen needed = 0.66666 24dm = 16.0 ()
(iii)
Calc�late the �ol�me of air that contains this �ol�me of o��gen.
[2]
Vol�me of air needed = 16.0 21 = 76.2 () (c)
(i)
State �h� ethene can be made into a pol�mer b�t ethane cannot.
[1]
Ethene is unsaturated and contains a C=C bond whereas ethane is saturated.
(ii)
Describe �hat happens �hen ethene molec�les �ndergo pol�merisation.
[2]
The C=C bond in each molecule will break, bre ak allowing each carbon atom to share break electrons with other ethene molecules, joining joining into a longchain polymer without an� loss of atoms. (iii)
Ded�ce and dra� the str�ct�ral form�la of the monomer from �hich the pol�mer sho�n belo� is made. Ded�ction: Monomer is �nsat�rated and contains C=C bond. All atoms in monomer are intact and can be fo�nd in the pol�mer. Str�ct�ral form�la :
C
H C H
=
C H
[2]
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SECTION B .
(a)
(i)
Name an� element from Period 2 and e�plain ho� the electronic str�ct�re of this element can be �sed to determine �hich gro�p it is in.
[3]
Element : Lithi�m It has 3 electrons in the atom �ith an electronic str�ct�re of 2. 2.1. 1 As s�ch, it has 2.1 1 �alence electron �hich placed it in Gro�p II of the Periodic Table.
(ii)
On mo�ing across Period 2, the character of the elements changes. Describe and e�plain the change.
[3]
Across the Period, the metallic metallic properties properties of elements elements decrease. decrease. As the n�mber of �alence electrons increase, the tendenc� of the atom to lose its �alence �alence electrons electrons to obtain stable stable noble gas config�ration decreases decreases from Gro�p I to VII. The elements from Gro�p IV to VII ha�e a greater tendenc� to gain electrons to obtain stable noble gas config�ration, and are considered less metallic metallic.
(b)
The element �ith an atomic n�mber of 5 is so �nstable that it has ne�er been seen b� the naked h�man e�e. Consider the properties of other elements in the same gro�p as this element. Predict one ph�sical and one chemical propert� of this element. Write a balanced chemical eq�ation to represent the chemical propert� that �o� ha�e described. Ph�sical propert� : Its stable form is a solid at room room temperat�re and press�re. press�re. Chemical propert� : It reacts �ith h�drogen gas to form gaseo�s h�drogen astatide astatide. Eq�ation :
+
[Note that �nstabilit� = radioacti�it� of astadine, �hich is a chemical propert�. A skilled St�dent St�dent ma� incl�de deca� of astadine to prod�ce heli�m as an eq�ation.]
[4]
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9.
(a)
The speed of a chemical reaction can be changed b� increasing the press�re of reacting gases, • decreasing the concentrations of reacting sol�tions. • (i) (ii)
State the effect that each of these has on the speed of reaction. Use �o�r kno�ledge of reacting particles to e�plain �o�r ans�er.
[5]
Press�re increases the the speed speed of reaction reaction. Press�re : (i) Increasing press�re increases (ii) At higher press�re, the �ol�me of of space space in �hich the reactant particles mo�e in decreases, th�s increasing �ol�me �me. increasing the the n�mber of particles per �nit �ol �me This increases the freq�enc� of collisions bet�een reactant particles, hence a higher chance of higher chance of effecti�e effecti�e collisions, res�lting in a faster reaction.. Concentration : (i) Decreasing concentration red�ces red�ces the speed of reaction. reaction. (ii) At a lo�er concentration, the n�mber of reactant particles particles per per �nit �nit �ol�me decreases. This decreases the freq�enc� of collisions bet�een reactant particles, hence a lo�er chance of effecti�e collision,, res�lting in a slo�er re action rate. effecti�e collision
[Aim to present ans�er �ell and clearl�.] (b)
An e�periment is to be carried o�t in the laborator� to meas�re the a�erage speed of a chemical reaction. (i) (ii)
(i)
Choose and briefl� describe a s�itable reaction. Describe the meas�rements �o� �ill make. Describe ho� �o� �ill determine the a�erage speed of �o�r reaction. State the �nits in �hich the speed of the reaction can be meas�red.
S�itable reaction : Meas�ring Meas�ring mass mass loss loss b� gas in the the reaction reaction mi�t�re mi�t�re against against time. time. Reaction carried o�t bet�een solid calci�m carbonate and dil�te nitric nitric acid. acid. Meas�rements : B� means of an electronic beam balance balance, the mass change of content in electronic beam a conical flask (�ith a �ool placed at th e mo�th) containing the reactants is meas�red against time taken �sing a stop�atch. stop�atch A mass mass��against against� graph. stop�atch against �time data is plotted into a graph. The mass loss recorded is d�e to carbon dio�ide prod�ced escape into s�rro�ndings.
(ii)
The a�erag a�eragee speed of reaction =
or the a�erage speed at a specific time
can be obtained b� calc�lating the gradient of c�r�e of graph. Units meas�red = g rams per �nit second (g/s)
[5]
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10.
Metals can be placed in a reacti�it� series. Altho�gh carbon is a non�metal, it can also be placed in the series. It is placed bet�een magnesi�m and lead. (a)
Metals are e�tracted in man� different �a�s. Use the series, �ith e�amples, e�amples to e�plain the follo�ing (i) some metals can occ�r in the gro�nd as the �ncombined metal, (ii) se�eral metals occ�r as o�ides. The metal can be e�tracted from some of these o�ides b� heating �ith carbon. For other o�ides, this method cannot be �sed.
[5]
(i) Metals fo�nd �ncombined are e�tremel� �nreacti�e �nreacti�e and and inert, copper metal metal. It is inert s�ch as copper placed belo� h�drogen in the series and can be e�tracted b� red�ction. b� h�drogen h�drogen red�ction red�ction Copper does not �ndergo o�idation in the presence of air to form o�ide hence can occ�r in the Gro�nd as the �ncombined metal. (ii) Metals that are abo�e h�drogen h�drogen in in the the series series are generall� reacti�e and o�idise readil� in air to form o�ides o�ides. Metals that can be e�tracted b� heating �ith carbon are belo� carbon s�ch as iron. iron Iron r�sts in moist air to form h�drated iron(III) iron(III) o�ide. o�ide Here, iron i s less reacti�e than carbon and can be displaced b� carbon from its o�ide. Ho�e�er, some metals abo�e carbon carbon in the series series cannot be e�tract b � carbon, s�ch as magnesi�m. magnesi�m It forms o�ide that it e�tremel� heat stable and can onl� be e�tracted b � electrol�sis. electrol�sis. [A trick� and dangero�s q�estion. Easil� �ritten o�t of conte�t.] (b)
(i) (ii)
Iron and calci�m req�ire different conditions to react �ith �ater. B� referring to these conditions, j�stif� the relati�e positions of iron and calci�m in the reacti�it� series. Write a balanced chemical eq�ation for one of the reactions �o� described.
(i) Calci�m Calci�m : It can react �ith distilled distilled �ater generall� in an� gi�en temperat�re. temperat�re For E�ample, calci�m reacts �ith both cold �ater and steam steam. Iron : It can onl� react �ith boiling boiling �ater �ater that has formed steam. steam Therefore, calci�m is more reati�e than iron and �ill be abo�e iron in the reacti�it� series. As calci�m can react �ith cold �ater b�t iron does not, it is considered an e�tremel� reacti�e metal and is placed abo�e carbon in t the he series and similarl�, iron iron placed belo� carbon in the series series. (ii) Eq�ation : Ca(s) + 2H O() Ca(OH) () + H ()
E N D
O F
P A P E R
[5]
