OCR
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RECOGNISING ACHIEVEMENT
OXFORDCAMBRIDGEAND RSA EXAMINATIONS
Advanced GCE
2816/01
CHEMISTRY
Unifying
Concepts
Friday
21 JANUARY2OO5
Morning
t hour15 minutes
Candidatesansweron the questionpaper.
Additionalmaterials:
Data Sheet for Chemistry
Scientificcalculator
CandidateName
TIME
CentreNumber
Candidate
Number
t hour15 minutes
INSTRUCTIONS
TO CANDIDATES
.
Writeyour namein the spaceabove.
r
Writeyour Centrenumberand Candidatenumberin the boxesabove.
.
Answerall the questions.
.
Writeyourans'v\rers
in the spacesprovidedon the questionpaper.
o Readeach questioncarefullyand makesure you knowwhat you haveto do beforestartingyour
ansurer.
INFORMATION
FORCANDIDATES
a
a
.
o
.
The numberof marksis givenin brackets
[ ] at the endof eachquestionor partquestion.
Youwill be awardedmarksfor the qualityof writtencommunication
wherethis is indicatedin the
question.
Youmayusea scientificcalculator.
FOR E X A MIN E R'SUSE
Youmay usethe Data Sheetfor Chemistry.
Max.
Mark
Qu
Youare advisedto showall the stepsin anycalculations.
1
15
2
17
3
12
4
16
TOTAL
60
fhis questionpaperconsistsof 10 printedpagesand2 blank pages.
sP (SLM/KS)576509/2
@oGR 2005 [U100t34281
RegisteredCharityNumber:1066969
[Turn over
2
For
Examinefs
Use
Answerall the questions.
1
In the UK,almostall the sulphuric
acid,H2SO4,
is manufactured
by the Contactprocess.
One stagein the Contactprocessinvolvesthe reactionbetweensulphurdioxideandoxygen.
2so2(g) + o2(g) +
2so3(g)
Table1.1belowshowsvaluesof the equilibrium
constanl,Kp,for thisequilibrium
at different
temperatures.
temperature
/ "C
KrlkPa-1
25
4.0 x 1022
200
2 . 5x 1 O B
800
1.3 x 1O-3
Table1.1
(a) Writean expression
for the equilibrium
constant,Kp,of this reaction.
t2l
(b) In thisquestion,
one markis available
for the qualityand useof scientific
terms.
.
Theconversion
of sulphurdioxideandoxygenintosulphurtrioxideis carriedout at
pressure.Commenton this statement.
slightlyaboveatmospheric
.
Explainwhat happensto the equilibriumamounts of SOr, Oz and SO. as
temperature
increasesat constantpressure.
.
Deducethe sign of LH for the fonruard
reactionin the equilibrium.
Explainyour
reasoning
carefully.
2816/01Jan05
For
Examinefs
Use
;;iil;;*;il;;;;;t;;;;; fi
(c) An equilibrium
is set up for the SO, 02,SO. equilibrium
at 400"C.
At thistemperature
.
partialpressure
theequilibrium
of SO, is 10kPa
.
partialpressureof O, is 50kPa
the equilibrium
'
Kp= 3.0x 102kPa-1.
Calculatethe equilibriumpartialpressureof SO. at 400"C. Hencedeterminethe
percentage
of SO. in the equilibrium
mixtureat thistemperature.
answer
.....%t3l
(d) In the UK, almost all the sulphuricacid manufactured
uses sulphuras a starting
materialfor SO, production.
ln somecountries,
metaloressuchas zincsulphide,
ZnS,
are usedinsteadto form SO, by heatingwithair.
(i) Constructa balancedequationto show the reactionthat takesplacewhen zinc
sulphideis heatedin air.
..121
(ii) Suggestwhy countriesmay find it more economicto manufacturesulphuricacid
from zinc sulphide.
2816/01Jan05
flurn over
4
One causeof low-levelsmog is the reactionof ozone,Os,with ethene.The smogcontains
is shownbelow.
methanal,CH2O(g),and the equationfor its production
o3(g)+ crHo(o)+ 2cHro(g)+ lorts)
For
Examinefs
Use
equation2.1
of eitherO3(g)or CrHa(9)
(a) The rateof the reactiondoubleswhenthe initialconcentration
is doubled.
(i) Whatis the orderof reactionwith respectto
03......
t1l
c2H4?
"""""'t1l
(ii) Whatis the overallorderof the reaction?
(iii) Writethe rateequationfor this reaction.
..t11
(b)
of ozone of 0.50 x 10-7 moldm-3 and one of etheneof
\v' For an initialconcentration
was 1.0x 10-12moldm-3s-1.
formation
io r io:d-rorotn:., tn" initialrateof methanal
(i) How could the initial rate of methanal formation be measured from a
graPh?
concentration/time
l2l
(ii)
Calculatethe value of the rate constantand state the units.
=...........
rateconstant
units..
........t31
(iii) The initialrate of methanalformationis differentfrom that of oxygenformationin
2.1.
equation
Explainwhy.
2816/01Jan05
5
(iv) The experimentwas repeatedbut at a highertemperature.
What wouldbe the
effectof this changeon the rateandthe rateconstantof the reaction?
For
Exaninefs
Use
..t21
(c) In the stratosphere, ozone forms when oxygen free radicals react with oxygen
molecules.
02 + O +
Og
The oxygen free radicalsare initiallyformed as diradicalswhen oxygen gas, Or, is
dissociatedby strong ultravioletradiation,
o2(s)-+ 2o(s)
(i) Suggestwhyoxygenfreeradicals,
O, areoftencalleddiradicals.
t1l
(ii)
of an ozonemolecule.Show outer electronsonly.
Draw a'dot-and-cross'diagram
tzl
(iii)
Chlorine free radicals formed from CFCs deplete the ozone layer in a chain
reaction.
Typically, 1 g of chlorine free radicals destroys 150kg of ozone during the
atmosphericlifetimeof the chlorinefree radical(one to two years).
Calculate how many ozone moleculesare destroyed in this chain reaction by a
single chlorinefree radicalbeforethe free radicalis destroyed.
answer..
2816/01Jan05
........t31
[Total:17]
[Turn over
6
3
Ph.e.nol,
C6H5OH,
is a powerfuldisinfectant
and antiseptic.Phenolis a weakBrsnsted-Lowry
acid.
(a) Whatis meantbythefollowing
terms;
(i) a Brsnsted-Lowry
acid;
rll
'.....t.J
(ii) a weakacid?
.. . t l1
(b) When phenol is mixed with aqueous sodium hydroxide,an acid-base reaction takes
place.
CuHuOH(aq)
+
OH-(aq)
;+
CuHuO-(aq)
+
H2O(t)
In the spacesabove,
o
'
labelone conjugateacid-basepair as acid 1 andbase1,
labelthe otherconjugateacid-basepair as acid2 andbase2.
t2l
(c) A solutionof phenolin waterhasa concentration
of 3gg dm-3.
Theaciddissociation
constant,K^,of phenolis 1.3x 10-10moldm-3.
(i) Writean expression
for the aciddissociation
constant,K^,of phenol.
t1l
2816/01Jan05
For
Examinefs
Use
7
For
Examine/s
Use
(ii) Calculate
the pH of thissolution.
answer..
....t5l
(d) Hexylresorcinol
is an antisepticused in solutionsfor cleansingwounds and in
mouthwashes
andthroatlozenges.
The structureof hexylresorcinol
is shownbelow.
cH2(cHz)+cHs
ldentify a compoundthat could be added to hexylresorcinolto make a buffer solution.
Explainyour answer.
t2l
[Total:12]
2816/01Jan05
[Turn over
For
Examinefs
Use
8
Titrationcurvescan be usedto decideon a suitableindicatorfor a titration.
Youaresuppliedwiththefollowingsolutions.
.
0.100moldm-3NaOH(aq)
whichhasa pH of 2'9
o Q.lo0moldm-3
CHsCOOH(aq),
addedto 25.0cm3of 0.100moldm-3
(a) so.gcm3of 0.100 moldm-3NaOH(aq)is gradually
CH3COOH(aq).
values,
sketchthe titrationcurvefor this addition.Labelthe axesandmarkapproximate
to showthe variationof PH.
t6l
is a suitableindicatorfor a titrationbetween CH3COOH(aq)and
(b) Phenolphthalein
whereasmethylorangeis not suitable.
NaOH(aq)
Explainthesetwo statements.
""'t2l
2816/01Jan05
For
Examinels
Use
9
(c) The procedurein (a) was repeatedwith 25.0cm30.050moldm-3CHTCOOH(aq)
instead
of 0.100moldm-3CH3COOH(aq).
Whatdifferences
wouldtherebe in the titrationcurveplotted?
...121
(d) Compound
B is an organicbase.A studentanalysedthis baseby the procedure
below.
He first prepareda solutionof B by dissolvinga32g of B in water and makingthe
solutionup to 250cm3.Thestudentthencarriedout a titrationin which25.00cm3of this
solutionof B wereneutralised
by exactly23.20cm3
of 0.200moldm-sHCl.
1 moleof B reactswith 1 moleof HC/.
Usethis information
to calculatethe molarmassof baseB and suggestits identity.
t6l
[Total:16]
END OF QUESTIONPAPER
2816/01Jan05