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FORM TP 2015156
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MAY/JUNE 2OI5
CARIBBEAN EXAMINATIONS COUNCIL
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CARIBBEAN ADVANCED PROFICIENCY EXAMINATION@
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CHEMISTRY
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2 hours 30 minutes
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READ THE FOLLOWING INSTRUCTIONS CAREFULLY.
l.
This paper consists of SIX questions in TWO sections. AnswerALL questions.
2-
write your answers in the spaces provided in this bookret.
3-
Do NOT write in the margins.
4-
where appropriate, ALL WORKING MUST BE sHowN in this booklet.
5.
A data booklet is provided.
6-
You may use a silent, non-programmable calculator to answer questions.
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If you need to rewrite any answer and there is not enough space to do so on the
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original page, you must use the extra lined page(s) provided at the back
ofthis booklet.
Remember to draw a line through your original answer.
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If you use the extra page(s) you MUST write the question number clearly in
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box provided at the top of the extra page(s) and, where relevant, include
the
question part beside the answer.
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DO NOT TURN THIS PAGE TJNTIL YOU ARE TOLD TO DO SO.
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Copyright @ 2014 Caribbean Examinations Council
All rights reserved.
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02 | 12020/0APE 201 s
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0211202003
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-2SECTION A
AnswerALL questions.
MODULE 1
FUNDAMENTALS IN CHEMISTRY
l.
(a)
(i)
Define the term 'bond energY'.
[1 markl
(i i)
The bond lengths and bond energies of carbon-carbon single, double and triple
bonds are listed below.
c-c
1.544
Bond Lengths
Bond Energy 348 kJ mol-'
C:C
rs4A
614 kJ
mol-'
c<
1.20A
839 kJ mol-'
State the relationship between the strength of a covalent bond and its length.
[1 markl
(b)
Bond energies can be used to estimate the enthalpies ofreactions in which bonds are broken
and new bonds are formed. Consider the gas-phase reaction between methane (CH) and
chlorine to produce methyl chloride (CH3CL) and hydrogen chloride.
(i)
Write a balanced equation to represent the reaction above.
[2 marks]
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0211202004
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(ii)
Using bond energy values from Table l, calculate the enthalpy change of reaction,
AHon, for the equation required in (b) (i).
TABLE 1: BOND ENERGY VALUES
Bond
Energy
(kJ mol-r)
H-H
436
F-F
158
cu-ct
244
H-F
562
H-C[
431
c-c
3s0
C-H
410
c-cI
340
c-o
360
S-H
347
[3 marksl
(iii)
Is the reaction in (b) (i) exothermic or endothermic?
[1 markl
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02112020/CAPE 2015
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0211202005
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-4(iv)
On the axes provided below, draw the energy-profile diagram for the reaction in
(b) (D.
Progress of reaction
[2 marksl
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0211202006
-5(c)
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A student is asked to determine the enthalpy ofthe neutralization reaction between 75 cm3
of 1.00 M hydrochloric acid and75 cm3 of I .00 M potassium hydroxide solution. Outline
the experimental steps (including calculations) required to obtain an accurate value.
[Assume that the densities of the solutions of acid and base and their heat capacities are
oC-r) of water.l
equal to the density (l g cma) and heat capacity (4.18 J g-r
[5 marksl
Total 15 marks
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021t2020/cAPE 20l s
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0211202007
-6MODULE 2
KINETICS AND EQUILIBRIA
(a)
2.
Define EACH of the following terms:
(i)
Standard electrode potential of a half-cell
i;;;;i
(ii)
Standard cell potential of an electrochemical cell
[2 marksl
(b)
Consider the following (unbalanced) equation which describes the process that is taking
place in an electrochemical cell under standard conditions.
A(s) + Sn2*(aq) -+ Al,3*(aq) + Sn(s)
(i)
Write the ionic half-equation forthe reaction taking place at EACH ofthe electrodes.
ANODE:
CATHODE:
(ii)
[2 marksl
Write the cell diagram.
[1 markl
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0211202008
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(iii)
Draw a well-labelled diagram of the electrochemical cell. Indicate the direction
of electron flow.
[6 marksl
(iv)
For EACH electrode shown in Table 2, select the Ee value to determine the Ee"",,.
TABLE 2: ELECTRODE POTENTIALS
Electrode Reaction
Eo at298 K (25 oC)
(volts)
Ag*+e-iAg
+0.80
A[3*+3e-€Al,
-1.66
Ba2*+2e-iBa
-2.90
Sn2* + 2e-
-t Sn
-0.14
Sna*+2e-+Sn2+
+0.15
[2 marksl
Total 15 marks
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02n2020/cAPE 2015
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o211202009
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-8MODULE 3
CHEMISTRY OF THE ELEMENTS
The Group IV elements exhibit oxidation states of *2 and +4 in their compounds.
3.
(a)
Complete Table 3 for the oxides of carbon and lead'
TABLE 3: OXIDES OF GROUP IV ELEMENTS
CO
CO,
Pbo
Amphoteric
Neutral
Acid/base nature
Pbo2
Stable
Thermal stability
+2
Oxidation state of Group IV element
[4 marks]
(b)
(i)
Explain the relative stabilities of the +2 oxidation states ofthe oxides ofcarbon
and lead.
[4 marksl
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0211202010
-9(ii)
Use the electrode potential value in the electrode reaction for lead ions, to explain
the relative stabilities of the +2 and +4 oxidation states of lead:
pb4* + 2e-
-------*
Pb2*. Ee: * 1.80 volts
[2 marksl
(c)
Describe what should be observed when
(i)
concentrated sodium hydroxide is added to solid lead(IV) oxide
[1 markl
(ii)
concentrated hydrochloric acid is added to solid lead(IV) oxide.
[2 marksl
(d)
Describe a test to identify Pb2* ions in solution.
[2 marks]
Total 15 marks
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02n2020/cAPE 20t 5
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0211202011
-10-
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SECTION B
AnswerALL questions.
MODULE 1
FUNDAMENTALS IN CHEMISTRY
4.
(a)
The atoms of certain elements contain nuclei in which the ratio of neutrons to protons is
These nuclei tend to emit radiation in order to bring the ratio closer to l.
greater than
l.
(i)
Describe the THREE types of radiation that an unstable atom may emit. Include
in your answer the symbols and penetrating power of EACH type of radiation'
[6 marksl
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02112020/0APE 2015
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0211202012
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Americium-241 (Am-241) decays via alpha particle emission. Write the nuclear
equations to show the new element that forms when an atom of 241- 6^ decays
95
via the emission of 2 alpha particles.
[2 marksl
(b)
(i)
Draw the diagrams of the atomic orbitals of principalquantum number 2. Include
x, y and z axes in your drawing.
[2 marksl
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021t2020/cAPE 2015
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0211202013
-12-
(ii)
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Comment on the similarity and difference in the electronic configurations of K,
Sc and Znz* given below.
K: ls2 2s2 2p6 3s2 3p6 4sl
Sc: ls2 2s2 2p6 3s2 3p6 3d' 4s2
Znz*: lsz 2sz 2p6 3s2 3p6 3dro
[5 marksl
Total 15 marks
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0211202014
- 13 _
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MODULE 2
KINETICS AND EQUILIBRIA
A buffer consisting of HrPOo- and HPO.2- helps control the pH of physiological fluids. Many
J.
carbonated soft drinks also use this buffer system.
(a)
Using the buffer system mentioned above, describe how the solution maintains an almost
constant pH even when small amounts of acid or alkali are added to the solution.
[6 marks]
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02r12020/cAPE 2015
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0211202015
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Catculate the pH of a soft drink in which the major buffer ingredients are 6.5 g ofNaHrPOo
and 8.0 g of NarHPOn per 355 cm3 of solution.
[K" (H2PO4)
:6-4 x l0-8 mol dm-3]
[Relative atomic mass: H
: l, Na : 23, O: 16, P : 3l ]
[5 marks]
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02n2020/cAPE 2015
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0211202016
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Many chemical reactions occur in living systems such as the human body. Discuss the
importance of biological buffers to the maintenance of a healthy body. (lnclude an example
of a chemical reaction of a blood buffer.)
[4 marks]
Total 15 marks
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02112020/CAPE 2015
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0211202017
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-16MODULE 3
CHEMISTRY OF THE ELEMENTS
(a)
The atomic and ionic radii of the Group II elements gradually increase down the group.
Outline the reasons for this trend.
[3 marksl
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0211202018
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(b)
Account for the variation in the melting points of the Group II elements from magnesium
to barium.
[4 marks]
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0211202019
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(c)
Table 4 shows the observations when 0.1 mol dm-3 solutions of the metal ions are treated
with I mol dm-3 NarSOn.
TABLE 4: OBSERVATIONS OF REACTIONS
Solution of Group II Cations
0.1 mol dm-3
Observations
with I mol dm-3 NarSOn
Mgt*
No precipitate
Ca2*
Thin, white precipitate
sf*
White precipitate
Ba2*
Thick, white precipitate
Account for the trend indicated in Table 4.
[5 marksl
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0211202020
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-19(d)
Explain the variation in the thermal decomposition of the nitrates of the Group II elements.
[3 marksl
Total 15 marks
END OF TEST
IF YOU FINISH BEFORE TIME IS CALLED, CHECK YOI]R WORK ON THIS TEST.
02r12020/cAPE 2015
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o21't202021
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-20 EXTRA SPACE
If you use this extra page, you MUST write the question number clearly in the box provided.
Question No.
o2r12020/cAPE 2015
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0211202022
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