This is for the Unit 4 of of Edexcel Edexcel Chemistry A2 Level. Level. Enjoy, and any feedback is very elcome.
4.! "ates of "eactions "eaction "ate # chan$e in amo%nt of reactants&'rod%cts reactants&'rod%cts 'er %nit time (%nits) *+ *! mol dm s -olloin$ a reaction •
$as vol%me 'rod%ced ($as syrin$e
•
mass lost (balance
•
colo%r chan$e (colorimeter
•
•
clock reaction (s%dden chan$e at 'artic%lar time means s'eci/c concentration of 'rod%ct has been reached reached * the shorter the time taken, taken, the faster the rate electrical cond%ctivity (n%mber of ions ill chan$e as reaction occ%rs
Concentration*Time 0ra'h "ate at any 'oint can be fo%nd by drain$ a tan$ent at that 'oint on the $ra'h and /ndin$ the $radient. 1rders 1rde rs of "eaction "eacti on The order of reaction reaction # ho the reactants reactants concentration aects aects the rate 3C"EA5E "EACTAT 6 "ATE 5TA75 T8E 5A9E 6 1":E" 1- ; 3C"EA5E "EACTAT 6 "ATE 3C"EA5E5 <7 ! -ACT1" 6 1":E" 1- ! 3C"EA5E "EACTAT 6 "ATE 3C"EA5E5 <7 2 -ACT1"5 6 1":E" 1- 2 7o% 7o% can only /nd the order of a reaction reaction =ex'erimentally= =ex'erimentally= 6 there there is 1 theoretical order system.
5ha'es of "ate*Concentration 0ra'hs tell yo% the order. order. ? > 4 + 2 ! ; time (s
> 4 + 2 ! ; @B @B
Col%mn 2
? > 4 + 2 ! ; time (s
Col%mn 2
Col%mn 2
? > 4 + 2 ! ; @B @B
Col%mn 2
? > 4 + 2 ! ; time (s
Col%mn 2
!; >
Col%mn2
; @B @B
E"1 1":E"
-3"5T 1":E"
5EC1: 1":E"
=sD%are brackets brackets indicate concentration. -or exam'le @B # concentration of . 8alf*life # time taken for half the reactant to react 3f the half life is constant # /rst order 3f the half life is do%blin$ # second order 7o% 7o% can also calc%late the half life %sin$ reaction reaction rates. -or -or exam'le, if yo%re $iven the rate constant (see belo and the order yo% can ork o%t half life (yo% dont need to kno ho, j%st to be aare of it "ate ED%ations "ate eD%ation # tell yo% ho the rate is aected by the concentrations of reactants. E.0. Rate = k[A] m[B]n Fhere) m # order of A
5ha'es of "ate*Concentration 0ra'hs tell yo% the order. order. ? > 4 + 2 ! ; time (s
> 4 + 2 ! ; @B @B
Col%mn 2
? > 4 + 2 ! ; time (s
Col%mn 2
Col%mn 2
? > 4 + 2 ! ; @B @B
Col%mn 2
? > 4 + 2 ! ; time (s
Col%mn 2
!; >
Col%mn2
; @B @B
E"1 1":E"
-3"5T 1":E"
5EC1: 1":E"
=sD%are brackets brackets indicate concentration. -or exam'le @B # concentration of . 8alf*life # time taken for half the reactant to react 3f the half life is constant # /rst order 3f the half life is do%blin$ # second order 7o% 7o% can also calc%late the half life %sin$ reaction reaction rates. -or -or exam'le, if yo%re $iven the rate constant (see belo and the order yo% can ork o%t half life (yo% dont need to kno ho, j%st to be aare of it "ate ED%ations "ate eD%ation # tell yo% ho the rate is aected by the concentrations of reactants. E.0. Rate = k[A] m[B]n Fhere) m # order of A
n # order of < nGm # overall order k # rate constant (alays the same for a reaction at s'eci/c tem' and 'ress%re, increase tem' # increase k # bi$$er val%e of k # faster reaction
EA9HLE Hro'anone G 3odine IJ 3odo'ro'anone G 8 G G 3* acid
(reaction occ%rs in
3nfo) -irst order ith res'ect to 'ro'anone and 8 G and Kero order ith res'ect to iodine "ate eD%ation # k@'ro'anoneB!@8GB!@iodineB; 5im'lify to "ate eD%ation # k@'ro'anoneB@8 GB ; is !
(beca%se anythin$ to the 'oer of
8o to calc%late rate constant from the orders and rate "earran$e to make k the s%bject and calc%late. Units of k can be fo%nd as yo% kno concentration is moldm *+ and rate is moldm * + *! s %sin$ a normal Mcancellin$N method. Usin$ data to ded%ce the order ! The ex'eriment) titrate sam'le sol%tions a$ainst sodi%m thios%lfate and starch to ork o%t the concentration of the iodine. "e'eat ex'eriment, chan$in$ only the concentration for 1E "EACTAT at a time. ex'erime ! 2 + 4 > ? O nt @'ro'ano ;.4 ;.P !.2 ;.4 ;.4 ;.4 ;.4 neB @iodineB ;.;;2 ;.;;2 ;.;;2 ;.;;4 ;.;;? ;.;;2 ;.;;2 G @8 B ;.4 ;.4 ;.4 ;.4 ;.4 ;.P !.2 8ere, /rst e chan$ed the concentration of 'ro'anone for ex'eriments !, 2 and +. Then, e chan$ed the concentration of iodine in ex'eriments 4 and >. Lastly, e chan$ed concentration of 8 G in ex'eriments ? and O. 2 -rom this table e can 'lot O Concentration*Time $ra'hs. -indin$ the $radient at time Kero for each of these 'lots ill $ive %s the 33T3AL rate of each. + Com'are the res%lts e.$. Ex'eriment ! 2 +
Chan$e com'ared to ex'eriment ! *** @'ro'anoneB do%bled @'ro'anoneB trebled
"ate of reaction
Chan$e
;.;++ ;.;?2
*** "ate do%bled
;.;Q2
"ate trebled
4 > ? O
@iodineB do%bled @iodineB trebled @8GB do%bled @8GB do%bled
;.;+4 ;.;+2 ;.;>P ;.;Q4
o chan$e o chan$e "ate do%bled "ate trebled
="eaction rates ont be exactly do%ble or treble d%e to ex'erimental errors etc. 4 o e can ork o%t the rate eD%ation) •
•
•
"ate is 'ro'ortional to @'ro'anoneB so the reaction is of order ! ith res'ect to 'ro'anone. "ate does not chan$e&is inde'endent of @iodineB so the reaction is of order ; ith res'ect to iodine. "ate is 'ro'ortional to @8 GB so the reaction is of order ! ith res'ect to @8GB.
"ate determinin$ ste' # sloest ste' in a m%lti*ste' reaction (if a reactant a''ears in the rate eD%ation it 9U5T be a rate determinin$ ste' incl%din$ catalysts hich may a''ear in a rate eD%ation H"E:3C3T315 The order of a reaction ith res'ect to a reactant shos the n%mber of molec%les that the reactant is involved in ith re$ard to the rate*determinin$ ste'. EA9HLE) rate # k@B@7B 2. 8ere, one molec%le of and 2 molec%les of 7 ill be involved in the rate determinin$ ste'. Chlorine free radicals in the oKone consist of 2 ste's) ClR($ G 1+($ IJ Cl1R($ G 1 2($
slo rate determinin$ ste'
Cl1R($ G 1R($ IJ ClR($ G 1 2($
fast reaction
Therefore, ClR and 1+ m%st be in the rate eD%ation as they are the reactants from the sloest ste'. "ATE # k@ClRB@1+B Hredictin$ 9echanisms) 1nce yo% kno hat the rate determinin$ reactants are, yo% can think abo%t hat reaction mechanism it follos. EA9HLE) 3f the rate eD%ation is) rate # k@B@7B And the to dierent mechanisms are) ! G 7 IJ 1"
2 IJ 7 G -rom the rate eD%ation, e kno that and 7 9U5T be in the rate determinin$ ste', therefore, its mechanism ! hich is the ri$ht one.
8alo$enoalkanes 6 %cleo'hilic 5%bstit%tion (5 8alo$enoalkanes can be hydrolysed by 18 * ions by n%cleo'hilic s%bstit%tion. This is here a n%cleo'hile (e.$. :OH- attacks a molec%le and is sa''ed&s%bstit%ted for one of the attached $ro%'s (e.$. Br δ-. 3n this case the Carbon ( Cδ+ to 8alo$en (Xδ- bond is H1LA" as halo$ens are m%ch more electrone$ative than the carbon so they dra in electrons makin$ the Carbon sli$htly&delta 'ositive. The bond looks like this) Cδ+ — Xδ-
Th%s, the carbon can be easily attacked by a n%cleo'hile ho likes 'ositive areas. This mechanism occ%rs)
=C*
• •
Hrimary 6 react by 52 here 2 molec%les&ions are involved in the rate determinin$ ste' 5econdary 6 react by 5! and 52 Tertiary 6 react by 5! here ! molec%le&ion is involved in the rate determinin$ ste'
7o% can see by the rate eD%ation if there are ! or 2 molec%les in the rate determinin$ ste', hich in t%rn, tells yo% if the mechanism is 5! or 52. EA9HLE) "ate # k@B@7B # 2 molec%les in rate determinin$ ste' # 52 # 'rimary&secondary halo$enoalkane 1" "ate # k@B # ! molec%le in rate determinin$ ste' # 5! # tertiary&secondary halo$enoalkane
Activation Ener$y Fe can calc%late the activation ener$y %sin$ the Arrheni%s eD%ation)
Fhere the relationshi' k # rate constant
(yo% dont have to learn this, j%st %nderstand EA # activation ener$y (S
T # tem'erat%re (
" # $as constant (P.+! S *!mol*!
A # another constant 5ome relationshi's to note) ! As EA increases, k ill $et smaller. Therefore lar$e activation ener$y, means a slo rate 6 this makes sense 2 As T increases, k increases. Therefore at hi$h tem'erat%res, rate ill be D%icker 6 this makes sense too 3f e MlnN both sides of Arrheni%s eD%ation,
e $et
ln k # 6 E A&"T G ln A (dont for$et, ln A is j%st a constant, a
n%mber
This looks a bit like) y # mx G c 3f e 'lot ln k (y a$ainst !&T (x, the $radient e 'rod%ce ill be 6E A&" (m. Then " is j%st a n%mber that e kno (P.+! S *!mol*! e can rearran$e and /nd the activation ener$y. EA9HLE) 3odine clock reaction 521P2* (aD G 23 * (aD IJ 251 42* (aD G 32 (aD "ate of reaction is inversely 'ro'ortional to the time taken for the sol%tion to chan$e colo%r i.e. increased rate # decreased time taken k V !&t Fe can say that !&t is the same as k (rate constant e can s%bstit%te !&t instead of k in Arrheni%s eD%ation and /nd the $radient a$ain to /nd a val%e EA.
and for
Catalysts Catalyst # increases rate of a reaction by 'rovidin$ an alternative reaction 'athay ith a L1FE" activation ener$y (E A. A catalyst ill be chemically %nchan$ed at the end of a reaction. Adv) 5mall amo%nt needed to catalyse a lot of reactions, also they are remade, th%s re%sable. :isadv) 8i$h s'eci/city to the reactions they catalyse. There are to ty'es of catalysts) 81910E1U5 CATAL75T5 These are catalysts in the same state as the reactants.
8ETE"10E1U5 CATAL75T5 These are catalysts in dierent 'hysical states to the reactants. They are easily se'arated from E.0. hen enKymes catalyse reactions 'rod%cts 6 011: in yo%r body, all reactants are aD%eo%s, Can be 'oisoned (i.e. a s%bstance this is a homo$eno%s catalysis. clin$s to a catalyst stron$er than the reactant o%ld, 'reventin$ reaction s'eedin$ %' exam'le) s%l'h%r in the 8aber 'rocess is a M'oisonN6
4.2 Entro'y Entro'y # a meas%re of ho m%ch disorder there is in a s%bstance, ho many dierent ays 'articles can be arran$ed. 5ystems are 91"E ener$etically stable hen di sorder&entro'y is 8308. EA9HLE) A $as ill ant to esca'e its bottle beca%se the room its in is m%ch bi$$er and the 'articles can be arran$ed in lots of dierent ays. SOLID
LIQUID
GAS
o randomness, 5ome randomness, some 9ost randomness, therefore loest entro'y. entro'y. hi$hest entro'y. W * W * e.$. 5 (821(s # O.4 S e.$. 5 (821(l # O; S e.$. 5 W (821($ # !PQ S * ! ! ! mol*! mol*! mol*! (see belo (see belo (see belo =ote that Kero entro'y ill only occ%r in a 'erfectly ordered crystal Aectin$ -actors) !. 9ore D%anta ('ackets of ener$y # 9ore ays to arran$e 'articles # 9ore entro'y 2. 9ore 'articles # 9ore arran$ements # 9ore entro'y. E.0. *J 27 2 moles of 7 'rod%ced from ! mole of therefore entro'y has increased +. 3ncrease in tem'erat%re # 3ncrease in ener$y # 9ore entro'y E.0. bit
* from solid to liD%id entro'y has increased
a
* from liD%id to $as entro'y has increased a lot 4. Com'licated&com'lex molec%les # more entro'y :E-33T315) 5tandard entro'y of a s%bstance, 5 W, is the entro'y of one mole of a s%bstance %nder standard conditions of 2QP and !atm. The %nits are S *!mol*!. Fe ex'ect exothermic reactions to be the s'ontaneo%s ones hoever some endt!erm"# reactions are $%ntane&$ too. This is to do ith entr%'. 3f entro'y is hi$h eno%$h, the reaction ill be s'ontaneo%s, hether the reaction is exo&endothermic. EA9HLE) a8C1+(s
G
8G(aD IJ
! mole
aG(aD
! mole ! mole
G
C12($
! mole
G
821(l ! mole
5olid
aD%eo%s ions
aD%eo%s ions
$as
liD%id 8ere, the 'rod%cts have hi$h entro'y states (e.$. $as and there are more moles (e.$. reactants to 'rod%cts # 2)+ And so, overall entro'y has increased # 5H1TAE1U5 (also de'ends on X8 6 see belo L(AR) *H(S(:
X5
# 5
*
X5total # X5sys G Fhere X5sys # Entro'y chan$e of a system, the entro'y chan$e beteen the reactants and the 'rod%cts X5s%rr # Entro'y chan$e of a s%rro%ndin$ X5total # Total entro'y chan$e, the s%m of the entro'y chan$es of the system and the s%rro%ndin$s EA9HLE) 8+($
G
8Cl($
IJ
84Cl(s X8 # *+!>kSmol*
3nfo) !
5W (8+($ # !Q2.+ S *!mol*! (84Cl(s # Q4.? S *!mol*!
,
5W (8Cl($ # !P?.P S *!mol*!
"nd entr%' . t!e $'$tem
/S$'$
= S%rd&#t$ - Srea#tant$
# Q4.? 6 (!Q2.+ G !P?.P # - 2P4.> S*!mol*! 0, "nd entr%' . $&rr&nd"n1$
5W
@ote) X8 # *+!>kSmol*! is in 3L1S1ULE5,
# * (*+!>;;;&2QP therefore x!;;;B # + !;>O S*!mol*! 2, "nd tta3 entr%' /Stta3
= /S$'$ + /S$&rr
# *2P4.> G !;>O # + OO2.> S *!mol*! anserB
@ote) m%st incl%de si$n (and %nits ith /nal
Fhen ill a reaction be s'ontaneo%s •
•
•
Total entro'y m%st increase
+ X5
# kinetically favo%rable (ants to react s'ontaneo%s
total
— X5total # kinetically stable (ill not react on its on not s'ontaneo%s
= 7o% can 'redict ionic com'o%nd sol%bility %sin$ the same idea if X5 total is 'ositive Y, if ne$ative E:1T8E"93C ex'eriments that are s'ontaneo%s) !
G
28 2Cl(s
IJ
!;821(l G
28+($
Fhen yo% add bari%m hydroxide to ammoni%m chloride) • •
5mell of ammonia $as Tem'erat%re dro's belo ;ZC
2 Cold 'ack 6 841+(s and 821(l 841+(s
I821(lIJ 84G(aD G 1+*(aD
Fhen yo% dissolve ammoni%m nitrate crystals in ater) Lookin$ at the states in both these ex'eriments, e have an 3C"EA5E in entro'y (from solids to liD%ids&aD%eo%s. These reactions are s'ontaneo%s E[E T81U08 the X5s%rr is ne$ative (beca%se if X8 is 'ositive for endothermic reactions the eD%ation of X5 s%rr means the overall X5 s%rr ill be ne$ative 6 see above eD%ation the X5 sys is 0"EAT E1U08 to overcome it, meanin$ X5 total ill be 'ositive still. :E-33T315) Thermodynamic stability 6 here the X5total is ne$ative, at "TH, the reaction ill sim'ly not occ%r. E.0. limestone 6J Ca1 G C1 2
inetic inertness 6 hen the X5 total of a reaction is 'ositive, a reaction can ha''en s'ontaneo%sly, hoever the rate of reaction at "TH is so slo beca%se the activation ener$y needed for it to start is so hi$h. E.0. diamond 6J $ra'hite The enthal'y chan$e of hydration, X8hyd 6 the enthal'y chan$e hen ! mole of aD%eo%s ions is formed from $aseo%s ions. E.0. a G($ IJ a G(aD The standard lattice enthal'y, X8Wlatt 6 the enthal'y chan$e hen ! mole of a solid ionic com'o%nd is formed from $aseo%s ions %nder standard conditions (2QP and !atm. E.0. a G($ G Cl*($IJ aCl(s The enthal'y chan$e of sol%tion, X8sol 6 the enthal'y chan$e hen ! mole of sol%te is dissolved in s%\cient solvent, so no f%rther enthal'y chan$e occ%rs on f%rther dil%tion. E.0. aCl(s IJ aCl(aD -actors affectin$ X8Wlatt A: X8hyd incl%de ! 3onic char$e
# lar$er char$e # more exothermic lattice ener$y # 91"E E0AT3[E LATT3CE ET8ALH7&ET8ALH7 187:"AT31
E.0. aCl has X8 Wlatt # *OP;kSmol *! hereas 9$Cl2 has X8Wlatt # *2>2?kSmol *! beca%se ma$nesi%m has a char$e of 2G hich is $reater than sodi%ms !G 2 3onic radii
# smaller ionic radii # more exothermic lattice enthal'y # hi$her char$e density # 91"E E0AT3[E LATT3CE ET8ALH7&ET8ALH7 187:"AT31
E.0. 5odi%ms ionic radi%s is bi$$er than ma$nesi%ms (beca%se 9$ has one more 'roton hich has a stron$er 'ositive n%clear attraction to its electrons 6 see %nit !&2 therefore ma$nesi%m ill have a more ne$ative lattice enthal'y&hydration enthal'y.
-indin$ the enthal'y of sol%tion
here e %se a similar 'rinci'le to 8ess La
X8! # X82 G X8+ R(4(4B(R 5.r X8sol ,: GAS(OUS IO)S DO6)7 AQU(OUS IO)S U8
G&n$ In
Detr"t7 A%%3e$ In Ukra"ne
4.+ ED%ilibria "ECAH) (for exothermic reaction Fhere does eD%ilibri%m move and hy
L( CHA*(LI(R %%$e t!e mt"n;
3ncrease Tem'erat%re
3ncrease Hress%re
3ntrod%ce Catalyst
Toard reactants, therefore less 'rod%cts 9ove to the endothermic side. 8i$her kinetic ener$y so more chance of s%ccessf%l collision L1F tem' # hi$h yield # b%t slo 'rocess... Toard side ith less molec%les of 1a$ (only aects $ases. Harticles are '%shed to$ether, hich increases chances of s%ccessf%l collision. 8308 'ress%re # hi$h yield # ex'ensive 1 E--ECT 1 E]U3L3<"3U9 H153T31 (ill aect rate
At eD%ilibri%m the amo%nt of reactants and 'rod%cts is the 5A9E. :ynamic ED%ilibri%m 6 a reaction that occ%rs in both ays at the same time (conditions in a closed system at constant tem'erat%re 9any ind%strial reactions are reversible e %se this si$n f or eD%ilibria) E.0.
Contact 'rocess 6 mak"n1 $&3%!&r"# a#"d 2512($ G 12($
251+($
U5E5 # fertilisers, dyes, medicines, batteries 2
8aber 'rocess 6 mak"n1 ammn"a 2($ G +8 2($
28+($
U5E5 # fertilisers, 'rod%cin$ nitro$en*based com'o%nds EHE"39ET) 8ydro$en*3odine "eaction
(R(9(RSIBL(,
There is a relationshi' beteen the concentration of initial reactants&'rod%cts and the eD%ilibri%m concentrations hich are 'rod%ced from them E.0.
82($ G 32($
283($
3nitial concentration)
82 # !.;moldm*+
ED%ilibri%m concentration)
82 # ;.22Pmoldm*+ 32 # ;.22Pmoldm*+
32 # !.;moldm*+
-rom this e can see that the ratio has remained the same, i.e. !)!
< % < # Fhat is ' & c ' & c is the ratio of 'rod%ct concentration to reactant concentration, and is commonly knon as the eD%ilibri%m constant. -or exam'le, in the hydro$en*iodine reaction c ill be =ote) 'rod%cts are 2 beca%se in a balanced eD%ation, there is a 2 in front 6 see belo E.0. 4
27 G +
=Fe can calc%late ' %sin$ 'artial 'ress%res (see belo
As lon$ as the eD%ilibri%m is 81910E1U5 (all reactants&'rod%cts in the same state then e can %se this $eneral r%le for /ndin$ c 3f the eD%ilibri%m is 8ETE"10E1U5 (here reactants&'rod%cts are in dierent states then yo% m%st LEA[E 1UT any concentrations that are $3"d. -or ', 81910E1U5 eD%ilibri%ms can be calc%lated %sin$ 3f the eD%ilibri%m is 8ETE"10E1U5 then yo% only take into acco%nt the $ases. =ote) e dont %se sD%are brackets for eD%ilibri%m 'artial 'ress%res
EHE"39ET)
-e2G(aD G A$G(aD
-e+G(aD G A$(s
! Add >;;cm+ of ;.!moldm*+ silver nitrate sol%tion to >;;cm + of ;.! moldm *+ of iron (33 s%lfate sol%tion 2 Leave mixt%re in sto''ered ^ask at 2QP, it ill reach eD%ilibri%m + Take sam'les and titrate
CALCULAT31) "eactant&Hrod%ct 3nitial concentration (moldm*+ ED%ilibri%m concentration (from titre res%lts ED%ilibri%m constant
-e2G(aD ;.;>
A$G(aD ;.;>
-e+G(aD ;
A$(s ;
;.;4+Q
;.;4+Q (!)! ratio
;.;;?! (;.;> 6 ;.;4+Q
solid
Units
Calc%latin$ 'artial 'ress%res 4"nt' r&"t$ *a$te 4"nt'
EA9HLE) Fhen +.; moles of HCl > is heated in a closed system, the eD%ilibri%m mixt%re has !.O> moles of Cl. 3f total 'ress%re of the mixt%re is O!4kHa, hat is the 'artial 'ress%re of HCl> 5te' ! -ind moles at eD%ilibri%m of all reactants and 'rod%cts Fe kno !.O> moles of Cl 2, therefore e m%st also have !.O> moles of HCl + and so (+ * !.O> ill leave %s ith the moles at eD%ilibri%m for HCl > hich is !.2> moles. Addin$ these to$ether e $et !.2>G!.O>G!.O> # 4.O> total moles at eD%ilibri%m. 5te' 2 -ind the mole fraction 1.25
9ole fraction of a $as in mixt%re #
4.75
5
#
19
# !.??
5te' + -ind 'artial 'ress%re 5
Hartial 'ress%re of $as # O!4 x
19
# !PO.QkHa
ED%ilibri%m and Entro'y are related
>Stta3 = R 3n< Fhen the total entro'y, _5 total, increases, the eD%ilibri%m constant, , ill also increase. 3f
# !;*!; # reaction ill not occ%r # !;*> # mostly reactants # ! # balanced 'rod%cts and reactants # !;> # mostly 'rod%cts # !;!; # reaction com'lete
4.O Acid&base ED%ilibria
-rom the timeline e can see the chan$e in de/nition of acids thro%$h history. The main ones to kno are) Arrheni%s de/nition 6 hen acids&bases dissolve in ater then com'letely&'artially dissociate into char$ed 'articles (ions
Acid
exam'le 8Cl($ IJ 8 G(aD G Cl *(aD a18(s G 821(l IJ a G(aD G 18*(aD
reason 5tron$ acids and bases ionise almost com'letely in ater. =8Cl has a '8 of ; # com'letely ionised
C8+C118(aD C8+C11*(aD G 8G(aD 8+(aD G 821(l 84G(aD G 18*(aD
Feak acids and bases only sli$htly ionise. ED%ilibri%m is set %' ith mostly reactants (to the left
Acid
Conj%$ate acid base 'airs • •
8A and A* are conj%$ate 'airs 821 and 8+1G are conj%$ate 'airs
6A*(R is s'ecial 6 it can behave as a base and an acid. 7o% can ork o%t the
eD%ilibri%m constant in the same manner as e did before e.$. 8oever, the eD%ilibri%m is very far left and so the eD%ilibri%m constant for this reaction is said to have a constant val%e
At 2QP&!atm, the c of ater is !.; x !;*!4 mol2dm*?
(Fe often de/ne this ith its on notation 6 < ? # c x @821B # the ionic 'rod%ct of ater # @8 GB@18*B ith U3T5) mol 2dm*? '8 6 M'oer of hydro$enN * is a meas%re of the hydro$en ion concentration
'8 # * lo$ CALCULAT31) /ndin$ the '8 of a $trn1 acid ! Calc%late the '8 of ;.;> moldm *+ of nitric acid. '8 # * lo$@8GB
'8 # * lo$@;.;>B # !.+
('8 val%e is small 6 ex'ected for a stron$
acid 2 An acid has a '8 of 2.4>, hat is the hydro$en ion concentration '8 # * lo$@8GB
@8GB # !;*'8 # +.>> x !;*+ moldm*+
=1TE) 82514 dissociates to $ive 2@8GB and yo% ill have to divide the /nal anser by 2 to /nd yo%r hydro$en ion concentration CALCULAT31) /ndin$ the '8 of a ?eak acid Feak acids do not f%lly dissociate so it isnt as strai$ht forard as above. Another constant called a is introd%ced. There are some ass%m'tions to make /rst) a 1nly a tiny amo%nt of 'rod%ct dissociates so initial concentration of reactant # eD%ilibri%m concentration of reactant b All 8G ions come from the acid i.e. concentration of 'rod%ct ! # concentration of 'rod%ct 2 ! Calc%late the hydro$en ion concentration and the '8 of a ;.;2 moldm *+ sol%tion of 'ro'anoic acid (C8 +C82C118. The a of 'ro'anoic acid is !.+ x !; * > moldm*+. a # @8GB2&@C8+C82C118B @8GB # >.;Q x !; *4 '8 # *lo$@>.;Q x !; *4B '8 # +.2Q
CALCULAT31) /ndin$ the '8 of a $trn1 base 1ne 18* ion f%lly dissociates 'er mole of base so the concentration of 18 * ions and concentration of the base is the $ame. 8oever to ork o%t '8 from the form%la, e need @8 GB. Therefore, e %se o%r knoled$e of ( 2QP, # !.; x !;*!4 mol2dm*? ! -ind the '8 of ;.! moldm*+ of a18 at 2QP. G
@8 B #
OH −¿ ¿ ¿ Kw
1.0 x 10 −14
#
0.1
# !.; x !; *!+ mol dm*+
¿
Therefore, '8 # *lo$ @!.; x !; *!+B # !+.; ('h val%e is lar$e 6 ex'ected for a stron$ alkali CALCULAT31) /ndin$ the ' a
' a # * lo$ ! Calc%late the '8 of ;.;>moldm*+ of methanoic acid (8C118. 9ethanoic acid has a ' a of +.O>. +.O> # *lo$@ aB
a # !.OP x !; *4
!.OP x !;*4 # @8GB2&@;.;>B
@8GB # 2.QP x !; *+
'8 # *[email protected] x !; *+B
'8 # 2.>+
Lastly, yo% sho%ld be aare that • •
dil%tin$ a stron$ acid (e.$. 8Cl by a factor of !; increases the '8 by ! dil%tin$ a eak acid (e.$. C8 +C118by a factor of !; increases the '8 by ;.> ! add a meas%re of acid (ith knon concentration to b%rette 2 ro%$h titration sirl conical ^ask for a''roximate end 'oint= + acc%rate titration dro' by dro' 4 record amo%nt of base needed to ne%tralise the acid > "e'eat for more acc%rate readin$s
=end 'oint) hen the sol%tion chan$es colo%r (also knon as eD%ivalence 'oint 6 see belo I)DICA*ORS
3ndicator
Colo%r in acid
9ethyl red oran$e 'henol'hthal colo%rles ein s
'8 hen colo%r chan$e +.!*4.4
Colo%r in alkali
P.+*!;
'ink
yello
a#"d %H a3ka3"
'8 C%rves Strn1 a#"dStrn1
8!en3%!t!a3e"n
6eak a#"dStrn1
Strn1 a#"d6eak
4et!'3 ran1e
6eak a#"d6eak
8!en3%!t!a3e"n
ED%ivalence 'oint # here a tiny amo%nt of alkali ca%ses a s%dden bi$ chan$e in '8, here the acid is SU5T ne%tralised. ED%ivalence 'oint ill vary de'endin$ on acid&alkali %sed. -or the last $ra'h beteen a eak acid and eak alkali, a '8 meter is the best thin$ to %se to /nd the eD%ivalence 'oint as the colo%r chan$e is $rad%al and %nclear. CALCULAT31) /ndin$ the a of a eak acid %sin$ a '8 c%rve
The half eD%ivalence 'oint is the 'oint here half the acid has been ne%tralised, here half the vol%me of stron$ base has been added the
At the half eD%ivalence 'oint @8AB # @A *B Therefore Th%s, e can say that the half eD%ivalence 'oint is also the ' a of the eak acid, then e can %se a # !;*'a
<%ers * * *
"E535T chan$es in '8 hen small amo%nts of acid&alkali are added :oesnt sto' the '8 from chan$in$ com'letely They only ork hen small amo%nts of acids&alkalis are added
AC3:3C
ALAL3E
m$t3' et!anate "n$
C8+C118(aD C8+C11*(aD G 8G (aD This n3' $3"1!t3' dissociates therefore m$t3' et!an"# a#"d ADDI)G ACID) (small amo%nt @8GB increases hich combines ith the C8+C11* to form C8 +C118 so eD%ilibri%m shifts to left, no chan$e in '8.
84G(aD 8G(aD G 8 +(aD This n3' $3"1!t3' dissociates therefore m$t3' ammn"&m
ADDI)G ACID) (small amo%nt
@8GB increases hich combines ith the 8+ to form 84 so eD%ilibri%m shifts to left, no chan$e in '8. ADDI)G AL
ADDI)G AL
@18*B increases hich combines ith the 8G to form 8 21 hich removes the 8G ions from sol%tion, so more 8 G dissociate from C8 +C118 so eD%ilibri%m shifts to ri$ht, no chan$e in '8.
@18*B increases hich combines ith the 8G to form 821 hich removes the 8 G ions from sol%tion, so more 8 G dissociate from 84G so eD%ilibri%m shifts to ri$ht, no chan$e in '8.
<%er
Cells 6 need constant '8 for biochemical reactions to take 'lace Controlled by the eD%ilibri%m beteen dihydro$en 'hos'hate and hydro$en 'hos'hate 82H14* 8H142*
-ood 'rod%cts 6 chan$es in '8 occ%r d%e to f%n$i and bacteria
Carbonic acid (82C1+
5odi%m citrate
82C1+ 821 G C12 L%n$s * by breathin$ o%t C12, levels of 8 2C1+ decrease and so eD%ilibri%m moves to the ri$ht
Citric acid citrate ions 1r Hhos'horic acid 'hos'hate ions 1r
8G G 82C1+
8G G 8C1+*
idneys control this eD%ilibri%m
CALCULAT31) A b%er sol%tion of ;.4 moldm *+ of
!. ED%ation for a
methanoic acid and ;.? moldm *+ sodi%m methanoate. for @8GB
2. "earran$in$
-or methanoic acid a# !.? x !;*4 moldm*+. Fhat is the '8 of the b%er
+. -ind '8
4.P -%rther 1r$anic Chemistry 3somers Str&#t&ra3) com'o%nds ith the same molec%lar form%lae b%t dierent
str%ct%ral form%lae Stere"$mer"$m:
1'tical
E&
mirror ima$es of each other, bonds here
only occ%rs in do%ble
they cannot be s%'erim'osed. i.e. $ro%'s are
rotation is restricted
=knon as
/xed in 'osition.
enantiomers
The chiral carbons has fo%r dierent
@*3519E"
(*
3519E" $ro%'s attached to it. *RA)S Mo''osite sidesN
CIS
MsameN
They are o'tically active (they rotate the heaviest
determined
'lane*'olarised li$ht 6 one ill rotate distrib%ted aro%nd
molec%les
by
side ho are
clockise and the other anticlockise.
the do%ble bond.
A ra#em"# mixt%re contains e&a3 &ant"t"e$ of each enantiomer of an %t"#a33' a#t"e com'o%nd (rotates %3ane %3ar"$ed 3"1!t . 1'tical Activity can be %sed to ork o%t a reaction mechanism. -or exam'le, n%cleo'hillic s%bstit%tion can occ%r in to dierent ays 3f a reaction is 5 and yo% start ith one enantiomer, the 'rod%ct ill be a racemic mixt%re of to o'tical isomers. The electrons move in the 'olar bond 5Cδ+ — Xδ-, move heterolytically to the Xδ- ( sta$e 3f a reaction is 5 0 and yo% start ith one enantiomer, the 'rod%ct ill be a sin$le enantiomer hich ill rotate the 'olarised li$ht. -irst the n%cleo'hile attacks a carbon and then the electrons in the 'olar bond 5Cδ+ — Xδ-, move heterolytically to the Xδ- (0 sta$es ="emember) from rates of reaction 5 means only molec%le ill be involved in the rate determinin$ ste' and 5 0 means there are 0 molec%les in the rate determinin$ ste'
Aldehydes and
etones
They do not hydro$en bond ith themselves as they dont have a 'olar O —Hδ+ bond. -or this reason, aldehydes and ketones have loer boilin$ 'oints than alcohols (hich can hydro$en bond δ-
They can hydro$en bond ith ater d%e to their 'olar Cδ+=Oδ- bond. 1xy$en %ses its lone 'air to form hydro$en bonds ith Hδ+ atoms on the ater molec%les. ote) small ketones&Aldehydes ill dissolve d%e to the 'olarity mentioned above, hoever lar$e ketones&Aldehydes ill have very stron$ intermolec%lar forces and ill not dissolve. UCLE1H83L3C A::3T31 8ydro$en cyanide is a eak acid 6 it 'artially dissociates in ater 8C
8G G C*
C* is a n%cleo'hile and attacks the sli$htly 'ositive carbon atom and donates its electrons to it. The electrons in the C#1 bond move to the oxy$en. 8 G from ater&hydro$en cyanide bond to the oxy$en formin$ 18. 1TE) 8C is a very toxic $as acidi/ed 'otassi%m cyanide is %sed to red%ce the risk. Ex'eriment m%st be cond%cted in f%me c%'board. Evidence of o'tical activity) carbonyl $ro%' is 'lanar n%cleo'hile can attack from either side. Asymmetric (not symmetrical ketone&aldehyde G C * IJ racemic mixt%re&to o'tical isomers. This is hat yo% ex'ect if the C can attack either side, 'rod%cin$ to dierent isomers. Tests to identify TE5T
3nfo 2,4* dinitro'heylhydraKine
etone
Aldehyde
Oran1e
Oran1e
Tollens rea$ent G heat (ater bath 6 not ^ame as ^ammable
Colo%rless sol%tion of silver nitrate dissolved in ammonia hich $ets red%ced and chan$es colo%r
o chan$e
S"3er m"rrr 5A15$,, A3de!'de "d"$ed
o chan$e
A15)H2,0+5a, + e- — A15$, +0)H2 5a,
-ehlin$s&
sol%tions
co''er(33 ions dissolved in a18(aD become C%G ions
'reci'itate (C%G ions Aldehyde oxidised
C&0+5a, + e- — C&+ 5a,
3odine in alkali G Hositive test # yello 'reci'itate heat 3f aldehyde 'ositive # ethanal (tests for C8 + on 3f ketone 'ositive # one end is C8 + carbon attached to oxy$en =1TE)
Aldehyde IJ Carboxylic acid Y @heat ith acidi/ed 'otassi%m dichromate ([3 ions (oxidisin$ a$entB colo%r chan$e) 1"A0E to 0"EE etone IJ Carboxylic acid @acidi/ed dichromate ([3 ions are not a stron$ eno%$h oxidisin$ a$entB R(DUCI)G: @LiAl84 in dry etherB
Aldehyde IJ Hrimary alcohol Carboxylic
etone IJ 5econdary alcohol
Acids
They hydro$en bond ith themselves as they do have a 'olar Oδ-—Hδ+ bond. -or this reason, carboxylic acids have very hi$h boilin$ 'oints. They can hydro$en bond ith ater d%e to their 'olar Cδ+=Oδ- bond. 1xy$en %ses its lone 'air to form hydro$en bonds ith Hδ+ atoms on the ater molec%les. Therefore, carboxylic acids are sol%ble, hoever as they $et bi$$er they become less sol%ble as the intermolec%lar forces $et too stron$. :imer)
hen a molec%le hydro$en bonds ith j%st one other molec%le, increasin$ the siKe and intermolec%lar forces of the molec%le, meanin$ the boilin$ 'oint is also hi$her.
9akin$ a carboxylic acid) ! Hrimary alcohol 6 oxidised 6 aldehyde 6 oxidised 6 carboxylic acid 2 itrile 6 hydrolysed (re^%x ith 8Cl then distil 6 distilled 'rod%ct is carboxylic acid "EACT315 1- CA"<17L3C AC3:5) )e&tra3"$at"nE
! C8+C118 G a18 IJ C8 +C11a G 821 ethanoic acid sodi%m ethanoate =1TE) C12 ca%ses
eervescence 2 2C8+C118 G a2C1+ IJ 2C8+C11a G 821 G C12 E.0. !2.> ml of ;.! moldm *+ of a18 exactly ne%tralises 2>ml of oran$e j%ice. Fhat is the concentration of citric acid in the j%ice +a18 G C?8P1O IJ a+C?8>1O G +821 ! -ind moles mols # conc x vol # ;.;!2> x ;.! # ;.;;!2>mols 2 -ind ratio&moles +mol a18 ne%tralised !mol citric acid +)! ;.;;!2> + # ;.;;;4!Omol + -ind concentration conc # mols vol ;.;2> ;.;;;4!O # ;.;!O moldm *+ Red&#t"nE ! C8+C118 ILiAl84 (in dry etherIJ 2C8 +18
2 C8+C118 G HCl> IJ C8+C1Cl G H1Cl+ G 8Cl ethanoic acid ethyl chloride 9akin$ an ester) Carboxylic acid G alcohol (heat&re^%x&acid catalyst
ester
3t is a reversible reaction so in order to $et the ester yo% m%st distil o the liD%id at P;ZC, and then mix ith sodi%m hydro$en carbonate sol%tion to remove any acid. Then se'arate the to' layer (ester %sin$ a f%nnel. U5E5) ethyl ethanoate is %sed as a solvent in chromato$ra'hy as ell as 'inea''le ^avo%rin$. amin$ the a3#!3 that as added comes Fr$t i.e. et!anol G methanoic acid ill 'rod%ce an ester call et!yl methanoate Acyl chlorides and
Esters
"EACT315 1- AC7L C8L1"3:E5
A93E ('rod%ce s%b*amide
FATE" ('rod%ce carboxylic acid
[iolent reaction at 2QP acyl chloride G C8 2 IJ C18 2C G 8Cl
* [i$oro%s reaction ith cold ater acyl chloride G 821 IJ C118 G 8Cl ALC181L ('rod%ce ester * [iolent reaction 2QP acyl chloride G 18 IJ C11C8 G 8Cl
=1TE) 8Cl $as is alays $iven o (observation
A9913A ('rod%ce amide * [iolent reaction at 2QP acyl chloride G 8 + IJ C182 G 8Cl
"EACT315 1- E5TE"5
Acid hydrolysis 6 addin$ ater so that the ester s'lits into an acid and an alcohol (reverse of makin$ ester %sin$ re^%x&heat&acid catalyst.
sodi%m salt (soa' that e %se every day Trans*Esteri/cation (TE H'dr1enat"n: addin$ hydro$en to remove the do%ble bonds. U$e: makin$ lo fat s'read from b%tter, biodiesel 8r3em: some trans isomers have been linked to vario%s diseases S3&t"n) to hydro$enation) trans*esteri/cation Ester G Alcohol IJ e ester
-ormin$ a 'olyester :icarboxylic acid
G
:iol
IJ
Holyester
G
Fater
4.Q 5'ectrosco'y and Chromato$ra'hy E9 "adiation) Favelen$th) Fhy) 8o)
Exam'le)
:an$er)
4"#r?ae$
U3tra"3et
!mm*!m 8eatin$ "adiation ca%ses electric /eld food (also 'olar e.$. fats, s%$ars rotate to line %' ith the /eld. :ryer food ith less ater content ill take lon$er to cook as ater has 'olar Oδ—Hδ+ bonds. Cookin$ 6 9icroave oven 5%r$ery 6 to kill cancer cells Chemical ind%stry 6 heatin$
4;;nm*!;nm 3nitiatin$ reactions 8as eno%$h ener$y to s'lit molec%les and 'rod%ce free radicals
n&a
3nitiatin$ reactions s%ch as s%bstit%tion beteen halo$en and alkane * Cl2 IU[IJ 2ClR * C-+Cl IU[IJ C-+ G ClR This initiation can ca%se one ClR can ca%se the destr%ction of to 1+ molec%les and another ClR 9assive chain reaction.
9ass 5'ectrosco'y The base 'eak is the !;; relative ab%ndance hich is %sed to /nd the "-9 9 'eak is ca%sed by the hole molec%lar ion hich breaks %' into fra$ments of free radicals and 'ositive ions, b%t only the 'ositive ion shos %' on a mass s'ectrometer. The other 'eaks are fra$ment ions of 5ome common "-9 of fra$ment ions)
C8+G C28?G C+8OG 18G C81G C118G
!> 2Q 4+ !O 2Q 4>
9" 5'ectrosco'y This $ives yo% information abo%t the str%ct%re %sin$ the idea that every atomic n%cle%s (ith an odd n%mber of 'rotons&ne%trons has a eak ma$netic /eld d%e to its n%clear s'in, and a''lyin$ a stron$ ma$netic /eld ill dis'lay accordin$ly. 8ydro$en is a sin$le 'roton and so e can %se 'roton 9" to /nd ho many hydro$ens there are and ho theyre arran$ed... ormally 'rotons are s'innin$ randomly, hoever hen yo% a''ly a S*RO)G (X*(R)AL 4AG)(*IC I(LD all the 'rotons line %'. 5ome 'rotons are ali$ned in the direction of the ma$netic /eld and others are o''osin$ it. Those %%$"n1 it are at a !"1!er ener1' 3ee3 and can em"t a rad"?ae to move to the loer ener$y level. Those in the direction of the ma$netic /eld are at a loer ener$y level and can absorb a radioave and move to a hi$her radioave. 9" meas%res the absor'tion of ener$y. Hrotons in dierent environments absorb dierent amo%nts of ener$y d%e to them bein$ shielded by electrons ex'eriencin$ the eects of the stron$ ma$netic force instead. Exam'les of dierent environments) 2
environments)
4 environments)
Chemical shift 6 is the dierence in absor'tion of a 'roton relative to Tetra9ethyl5ilane (5i(C8 +4. Fhere # ; is the val%e of T95. Each 'eak # one environment. 3n the $ra'h o''osite, there are to environments (2 'eaks The 3e$$ $!"e3ded a 'roton is, the .&rt!er 3e.t the shift ill be. 5'in*s'in co%'lin$ 6 in hi$h res, the 'eaks of an 9" %s%ally s'lit into smaller 'eaks, this is beca%se the ma$netic /eld of nei$hbo%rin$ 'rotons interact. The 'eaks follo an n+ r&3e hereby 2 s'lits @do%bletB # ! nei$hbo%rin$ 'roton (or hydro$en + s'lits @tri'letB # 2 nei$hbo%rin$ 'rotons (or hydro$ens 4 s'lits @D%artetB # + nei$hbo%rin$ 'rotons (or hydro$ens
