BARCODE
SCHOOL OF CHEMISTRY & PHYSICS
UNIVERSITY OF KWAZULU-NATAL
CHEM120: CHEMICAL REACTIVITY
DECEMBER 2016 MAIN EXAMINATION
Duration: 3 hours Total: 100 marks
SECTION B
Student No. Seat Number:
Instructions:
Part A consists of multiple choice questions and should be answered directly on the MCQ sheet
provided by making a circle over the most correct answer.
Part B requires written answers and should be answered directly on this question paper.
Answer all questions.
Non-programmable calculators are permitted for calculations
There are 25 pages (including a Periodic Table and Data Sheet) in total; check that you have them
all.
Internal Examiners WVL: Dr V Paideya (Coordinator) and Dr M Shozi
Internal Examiners PMB: Dr S Sithebe (Coordinator), Dr D Reddy and Dr B Xulu
Moderators: Dr N Nombona (WVL), Dr R Moodley (WVL), Mr M Rasalanavho (PMB)
Question A B1 B2 B3 B4 B5 B6 B7 B8 B9 Total
Internal Marks
50 5 9 7 4 8 4 5 3 5 100
External Marks
50 5 9 7 4 8 4 5 3 5 100
Rule 9 (1)(e) WARNING: CANDIDATES WILL BE DISQUALIFIED IF:
(a) they introduce, or attempt to introduce, into any place where an examination is about to be conducted or is being conducted, any paper, book, note,
document or instrument, the use of which is not authorized by the examiner or the examination officer.
(b) they possess, use, or attempt to use during an examination, any paper, book, note, document or instrument the use of which is not authorized by the examiner
or the examination officer.
(c) they remove or attempt to remove from the examination room, any examination book or writing paper supplied by the University for the purposes of answering
an examination.
(d) they communicate or attempt to communicate any information relating to the examination to another candidate while the examination is in progress.
(e) they use a false name or identity number in an examination.
(f) they commit any other fraudulent, deceitful or dishonest practice which would mislead or deceive the examiner or examination officer.
IF A STUDENT IS FOUND GUILTY BY A STUDENT DISCIPLINE COURT OF CONTRAVENING THE ABOVE RULE –9(1)(e) – SHE/HE WILL SUFFER ONE OR MORE OF
THE FOLLOWING CONSEQUENCES:
(i) Disqualification from entry to any examination.
(ii) Cancellation or forfeiture of examination results.
(iii) Deprivation of a degree, diploma or certificate obtained as a result of the offence.
University of KwaZulu-Natal, School of Chemistry and Physics
December 2016 Main Examination Session, CHEM120: Chemical Reactivity
QUESTION 1
(a) Name the following compound using the Cahn-Ingold-Prelog nomenclature and
indicate R or S configuration.
(2)
CH2Br
C CH2CH2Cl
H3CH2C OH
(b) Name the following compound, and assign E or Z configuration. (2)
Cl
(c) Draw the line structure for 2-methoxypentanoic acid. (1)
2
University of KwaZulu-Natal, School of Chemistry and Physics
December 2016 Main Examination Session, CHEM120: Chemical Reactivity
QUESTION 2
(a) Give the complete mechanism for the reaction of the acid-catalysed addition of
water to propene showing the formation of the most stable product.
(4)
(b) Complete the following reactions by filling in the answers for A‒E: (5)
(i) A
A=
(ii)
OH H2 SO4 B C
+
major minor
B= C=
(iii) D
CrO3 D=
+
H
3
University of KwaZulu-Natal, School of Chemistry and Physics
December 2016 Main Examination Session, CHEM120: Chemical Reactivity
(iv) O
E
OH OH
E=
[9]
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University of KwaZulu-Natal, School of Chemistry and Physics
December 2016 Main Examination Session, CHEM120: Chemical Reactivity
QUESTION 3
(a) A 15.34 g sample of an unknown organic compound was dissolved in 100.0 g of
benzene. The boiling point of the solution was found to be 83.12 oC. Determine
the molar mass of the compound. The normal boiling point of benzene is
78.51 oC, and Kb is 2.53 K kg mol-1.
(3)
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University of KwaZulu-Natal, School of Chemistry and Physics
December 2016 Main Examination Session, CHEM120: Chemical Reactivity
(b) At 29.6 °C, pure water has a vapour pressure of 31.1 torr. A solution is prepared
by adding 86.8 g of "Y", a nonvolatile non-electrolyte to 350 g of water. The vapour
pressure of the resulting solution is 28.6 torr. Calculate:
(i) the mole fraction of the solvent. (1½)
(ii) the number of moles of “Y”. (1½)
(iii) the molar mass of “Y”. (1)
[7]
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University of KwaZulu-Natal, School of Chemistry and Physics
December 2016 Main Examination Session, CHEM120: Chemical Reactivity
QUESTION 4
If NH4HS is placed in a flask already containing 0.020 mol dm-3 of NH3 and then the
system is allowed to come to equilibrium, what are the equilibrium concentrations of
NH3 and H2S? Kc = 1.8 x 10-4
NH4HS(s) ⇌ NH3(g) + H2S(g)
[4]
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University of KwaZulu-Natal, School of Chemistry and Physics
December 2016 Main Examination Session, CHEM120: Chemical Reactivity
QUESTION 5
(a) Calculate the pH of a 1.000 dm3 buffer solution composed of 1.050 M
ethylamine (C2H5NH2) and 0.9250 M ethylammonium chloride (C2H5NH3Cl).
Kb (C2H5NH2) = 4.27 x 10-4
C2H5NH2 + H2O ⇌ C2H5NH3+ + OH‒
(4)
(b) Calculate the pH of the buffer in (a) if 0.05000 mol of HCl are added. Assume no
volume change.
(4)
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University of KwaZulu-Natal, School of Chemistry and Physics
December 2016 Main Examination Session, CHEM120: Chemical Reactivity
QUESTION 6
The solubility of AlCl3 (133.34 g mol-1) at 25 °C is 50 mg per 1.00 L of water.
Calculate Ksp.
[4]
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University of KwaZulu-Natal, School of Chemistry and Physics
December 2016 Main Examination Session, CHEM120: Chemical Reactivity
QUESTION 7
To calibrate a calorimeter, 5.500 kg of water was added to the bomb, then a sufficient
amount of a particular compound was burned to produce 10.65 kJ of heat. The
temperature of the water was observed to rise by 0.440 C. Calculate is the heat
capacity of the bomb. Specific heat capacity of water = 4.18 J g-1 oC-1
[5]
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University of KwaZulu-Natal, School of Chemistry and Physics
December 2016 Main Examination Session, CHEM120: Chemical Reactivity
QUESTION 8
A current of 0.800 A is passed through an electrolytic cell containing molten
CrCl3 (158.35 g mol-1) for 2.50 hours. In the process, the chromium is reduced to the
element. Calculate the mass of chromium produced at the electrode.
[3]
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University of KwaZulu-Natal, School of Chemistry and Physics
December 2016 Main Examination Session, CHEM120: Chemical Reactivity
QUESTION 9
Consider the following reaction at 25 °C:
2ClO2(aq) + 2OH(aq) ClO3 (aq) + ClO2 (aq) + H2O(ℓ)
Using the data below obtained from a kinetic study of this reaction:
[ClO2]0 [OH–]0 Initial Rate
Experiment
(mol L-1) (mol L-1) (mol L-1 s-1)
1 0.050 0.100 0.0575
2 0.100 0.100 0.230
3 0.100 0.050 0.115
Derive the rate law for this reaction and subsequently determine the rate constant, k,
for the reaction at this temperature. Show ALL working!
[5]
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