SCHOOL OF CHEMISTRY & PHYSICS

UNIVERSITY OF KWAZULU-NATAL, WESTVILLE CAMPUS

CHEM120W2: CHEMICAL REACTIVITY
OCTOBER 2019 MAIN EXAMINATION

DURATION: 3 HOURS TOTAL MARKS: 100

SECTION A
Internal Examiners: Dr PB Khoza (Coordinator), Dr ML Shozi (Coordinator), Prof MD Bala
and Prof VO Nyamori

Moderators: Prof W van Zyl, Dr C Koorbanally and Dr R Moodley

INSTRUCTIONS:

1) For each of the following questions, select the correct answer from the list provided.
2) There is only ONE correct answer for each question.
3) Indicate your answer on the multiple choice answer sheet provided.
4) Make a dark heavy mark with HB pencil that fills the block of the appropriate letter
completely.
5) Answer ALL questions.
6) Calculators may be used.
7) Your answers to section A must be written on the MCQ sheet provided.
8) Use HB Pencil and note that Tipp-ExTM is not allowed on the MCQ sheet.
9) This is Section A: Multiple Choice Questions, consisting of 48 questions on 21 pages.
Ensure you have all pages.
10) You are advised to spend no more than 2 hours on Section A.
11) A periodic table and a data sheet are provided.

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
School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

Choose the most correct answer for each of the following multiple choice questions.
Colour your answer in (using an HB pencil) on the MCQ CARD provided.

1. Arrhenius defined an acid as:

(A) a species that can donate a proton.

(B) a species that can accept a proton.

(C) a source of OH- ions in water.

(D) a source of H+ ions in water.

[1]

2. According to the Brønsted–Lowry definition, bases, when reacting with acids:

(A) donate protons.

(B) form hydronium ions.

(C) accept protons.

(D) accept electrons.

[1]
– –
3. Identify the acids in the reaction: CN + H2O →
 HCN + OH

–
(A) CN and H2O

(B) H2O and HCN

–
(C) H2O and OH

–
(D) HCN and OH

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

4. Identify the set of products expected from the hydrolysis of NH4+ ion:

(A) NH4+ and OH–

(B) NH4+ and H2O

(C) NH3 and H3O+

(D) NH4+ and H3O+

[1]

5. According to the Brønsted–Lowry definition, which of the following chemical

species can function both as an acid and as a base?

–
(A) Cl

–
(B) HCO3

+
(C) NH4

(D) SO42-

[1]

6. Select the set of Brønsted–Lowry acids in the system below:

+ –
CH3COOH + H2O →
 H3O + CH3COO

(A) CH3COOH and H3O+

(B) CH3COOH and CH3COO–

(C) H2O and CH3COO–

+
(D) H3O and CH3COO–

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

7. Use the given pKb values below to choose the strongest base from the given
options:

(A) Ammonia (pKb = 4.7)

(B) Pyridine (pKb = 8.8)

(C) Diethylamine (pKb = 3.2)

(D) Aniline (pKb = 9.1)

[1]

8. The pH of a 0.03 M HCl solution is:

(A) 1.5

(B) 2.5

(C) 3.5

(D) 12.5

[1]

9. How many moles of pure NaOH is required to prepare 10 L of a solution that

has a pH of 13?

(A) 1.0

(B) 0.10

(C) 0.010

(D) 0.0010

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

10. The pOH of a solution of NaOH is 11.30. What is the [H+] for this solution?

(A) 2.0 x 10-3

(B) 2.5 x 10-3

(C) 5.0 x 10-12

(D) 4.0 x 10-12

[1]

11. A solution in which [H+] = 10-7 M has a pOH of ___ and is ___.

(A) 6, basic

(B) 7, neutral

(C) -8, acidic

(D) -6, basic

[1]

12. Which of the following is true about a 0.10 M solution of a weak acid, HX?

(A) [X-] = 0.10 M

(B) pH = 1

(C) [HX] > [H+]

(D) [H+] = 0.10 M

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

13. Consider the phase diagram below of a pure compound.

Which statement is correct?

(A) The path A → C represents sublimation.

(B) Following the path A → B → C the compound would first liquefy and then

vaporize.

(C) If the compound is in state A, continued reduction of the pressure (at

constant temperature) will cause it to melt.

(D) None of the statements (A-C) is correct.

[2]

14. Determine the molality of a solution prepared by the addition of 0.40 mol of a
solute to 250 g of water.

(A) 1.6 mol L-1

(B) 0.16 mol L-1

(C) 1.6 mol kg-1

(D) 0.80 mol kg-1

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

15. A 0.5 M aqueous solution is made of each of the substances listed below.
Which would have the highest freezing point?

(A) NaCl

(B) K2SO4

(C) Na3PO4

(D) CaCl2

[1]

16. When 12.5 mol of a non-electrolyte solute was added to 3.0 L of water, the
boiling point of the aqueous solution was found to be 102.4 °C. Based on this
information calculate the molal boiling point elevation constant.

(A) 0.6 °C m-1

(B) 6.0 °C m-1

(C) 2.4 °C m-1

(D) 4.2 °C m-1

[2]

17. When 0.60 moles of ascorbic acid is dissolved in 1500 mL of water, at what
temperature will the solution have an osmotic pressure of 9.0 atm?

(A) 247 K

(B) 375 K

(C) 274 K

(D) 300 K

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

18. When the system A + B ⇌ C + D is at equilibrium,

(A) neither the forward nor the reverse reaction has stopped.

(B) the forward reaction has stopped.

(C) both the forward and the reverse reactions have stopped.

(D) the reverse reaction has stopped.

[1]

19. What would be the effect of adding sodium benzoate to a solution of benzoic
acid?
1. The pH increases.
2. The concentration of benzoic acid increases.
3. The concentration of H3O+ increases.

(A) 1 only

(B) 2 only

(C) 1 and 2

(D) 1 and 3

[2]

20. Which one of the following sets of chemicals would NOT make a buffer
solution?

(A) NH4Cl and NH3

(B) HCN and KCN

(C) NaHCO3 and Na2CO3

(D) HCl and NaCl

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

21. A 25.0 mL sample of an unknown HBr solution is titrated with 0.100 M NaOH.
The equivalence point is reached upon the addition of 18.88 mL of the base.
What is the concentration of the HBr solution?

(A) 0.0755 M

(B) 0.0376 M

(C) 0.100 M

(D) 0.00188 M

[2]

22. Given the reaction below:

1
𝐻2 (𝑔) + 2𝑂2 (𝑔) → 𝐻2 𝑂(𝑙) ∆𝐻 ° = −285.8 𝑘𝐽

What quantity of heat is evolved when 100.0 g of 𝐻2 𝑂(𝑙) is formed from the
combustion of 𝐻2 (𝑔) and 𝑂2 (𝑔)?

(A) 51.44 kJ

(B) 285.8 kJ

(C) 1586 kJ

(D) 2297 kJ

[2]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

23. Hydrogen and fluorine react as follows:

𝐻2 (𝑔) + 𝐹2 (𝑔) → 2𝐻𝐹(𝑔) ∆𝐻 ° = −271 𝑘𝐽 𝑚𝑜𝑙 −1

If H2 (g) and F2 (g) are mixed in a thermally insulated vessel, the reaction that
occurs would be:

(A) exothermic, and the temperature of the reaction system would rise.

(B) endothermic, and the temperature of the reaction system would rise.

(C) exothermic, and the temperature of the reaction system would fall.

(D) endothermic, and the temperature of the reaction system would fall.

[2]

24. An electrochemical cell, prepared using iron and nickel, has the following cell
notation:
Fe(s)  Fe2+(aq)  Ni2+(aq)  Ni(s)
Which of the following represents the correctly balanced reaction equation for
the cell?

(A) Fe(s) + Fe2+(aq) → Ni2+(aq) + Ni(s)

(B) Fe(s) + Ni2+(aq) → Fe2+(aq) + Ni(s)

(C) Fe(s) + Ni(s) → Ni2+(aq) + Fe2+(aq)

(D) Fe2+(aq) + Ni(s) → Fe(s) + Ni2+(aq)

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

25. Which of the following halogens is the most easily reduced species?

Half Reaction ο
Ered

F2(g) + 2e– → 2F–(aq) +2.87

Cl2(g) + 2e– → 2Cl–(aq) +1.359
Br2(l) + 2e– → 2Br–(aq) +1.065

(A) F2

(B) Cl2

(C) Br2

(D) F–

[1]

26. Calculate the standard free energy change (ΔG°) for the following reaction:
4Ag+(aq) + 2H2O(l) → 4Ag(s) + O2(g) + 4H+(aq)
Given:
Ag+(aq) + e– → Ag(s) 𝜊
𝐸ox = 0.80 V
O2(g) + 4H+(aq) + 4e– → 2H2O(l) 𝜊
𝐸red = 1.23 V

(A) –166 kJ

(B) +166 kJ

(C) –1.66 x 105 kJ

(D) +41.5 kJ

[2]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

27. The standard free energy change (ΔG°) for the following reaction is 86.8 kJ.
Calculate the equilibrium constant, K, at 298 K for the following reaction:

3Ni2+(aq) + 2Cr(OH)3(s) + 10 OH–(aq) → 3Ni(s) + 2CrO42–(aq) + 8H2O(l)

(A) 9.66 x 10-1

(B) 1.63 x 1015

(C) 6.12 x 10–16

(D) 9.33 x 10–36

[2]

28. A spontaneous reaction will have which of the following characteristics?

(A) 𝐸cell
𝜊
> 0; G < 0; K > 1

(B) 𝐸cell
𝜊
< 0; G > 0; K < 1

(C) 𝐸cell
𝜊
> 0; G > 0; K > 1

(D) 𝐸cell
𝜊
= 0; G = 0; K = 1

[1]

29. Consider the reaction: 2𝑁𝑂(𝑔) + 𝐶𝑙2 (𝑔) → 2𝑁𝑂𝐶𝑙(𝑔). It was found that
doubling the concentration of chlorine results in doubling of the rate. When
the concentrations of both reactants are doubled, the rate increases by a
factor of 8. We can therefore say that the reaction is:

(A) first-order with respect to NO and first-order with respect to Cl2.

(B) first-order with respect to NO and second-order with respect to Cl2.

(C) second-order with respect to NO and second-order with respect to Cl2.

(D) second-order with respect to NO and first-order with respect to Cl2.

[2]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

30. Consider the following reaction:

2𝑁𝑂(𝑔) + 2𝐻2 (𝑔) → 𝑁2 (𝑔) + 2𝐻2 𝑂(𝑔)

The rate law for this reaction is found to be second-order with respect to NO

and first-order with respect to H2. When [𝑵𝑶] is 0.420 M and [𝑯𝟐 ] is 0.122 M,

the rate of appearance of N2 is 0.136 M s-1. What is the value of the rate

constant, k?

(A) 0.0459 M-2 s-1

(B) 0.158 M-2 s-1

(C) 0.377 M-2 s-1

(D) 6.32 M-2 s-1

[2]
31. What bonds are present in ethyne, C2H2?

(A) four sigma bonds and one pi bond

(B) two sigma bonds and three pi bonds

(C) three sigma bonds and two pi bonds

(D) seven sigma bonds

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

32. The ethyne molecule, C2H2, has a structure best described by the term

(A) cubic.

(B) linear.

(C) tetrahedral.

(D) trigonal planar.

[1]

33. What are the functional groups present in the following molecule?

(A) amine, aldehyde, ester

(B) amine, ketone, ester

(C) amide, ketone, ether

(D) aldehyde, amide, ether

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

34. What type of alcohol is the following molecule?

HO

(A) primary

(B) secondary

(C) tertiary

(D) methyl

[1]

35. Choose the condensed structural formula for 3-bromopentane

(A) CH3CH2CHBrCH2CH2CH3

(B) CH3CHBrCH2CH2CH2CH3

(C) (CH3)3CHBrCH2CH3

(D) CH3CH2CHBrCH2CH3

[1]
36. Isobutane differs from butane in that the former

(A) has a higher molecular weight.

(B) has a different percentage composition.

(C) is not a saturated hydrocarbon.

(D) has a different structural formula

[2]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

37. The correct IUPAC name for the molecule below is:

(A) 3-methyl-4-propyl-5-octanone

(B) 6-methyl-5-propyl-4-octanone

(C) 4-secbutyl-5-octanone

(D) 5-secbutyl-4-octanone

[2]
38. Which notation best describes the stereochemistry of the following
molecule?
Br

H
H3 C
OH

(A) E-

(B) Z-

(C) R-

(D) S-

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

39. Which one of the following statements is incorrect?

(A) A nucleophile is an electron rich species.

(B) An electrophile is a positively charged species.

(C) In heterolytic cleavage, two electrons in a cleaved covalent bond are

divided equally between the products.

(D) The products of homolytic cleavage are radicals.

[1]

40. In the following trichloromethyl anion, the chlorine atoms stabilise the
carbanion through:

Cl C Cl

Cl

(A) inductive electron dissociation

(B) inductive electron withdrawal

(C) inductive electron donation

(D) resonance structure

[1]

41. Which statement about hydrocarbons is incorrect?

(A) Alkanes undergo combustion.

(B) Alkanes can be produced by hydrogenating alkenes.

(C) Cyclic alkanes are structural isomers of alkenes.

(D) Alkanes are more reactive than alkenes.

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

42. What is the nucleophile in the reaction shown below?

CH3 CH3

C I + 2 H2O C OH + H3O+ + I-

NO2 NO2

(A) H2O

(B) H3O+

(C) NO2

(D)

[1]

43. Which of the following alcohols is oxidised to a ketone by chromic acid?

NH HO
HO OH
HO

(A) (B) (C) (D)

[1]

44. Which of the following will undergo an addition reaction with bromine?

(A) CH3-CH2-OH

(B) CH3-CH2-ONa

(C) CH2=CH-CH3

(D) CH3-CH2-COOH (propanoic acid)

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

45. The following amine can be classified as a:

NH2

Cl NO2

(A) secondary amine

(B) quaternary amine

(C) tertiary amine

(D) primary amine

[1]

46. What is the major product of the following reaction?

CH3
H2O
+ ?
+
H

CH3
CH2OH
(A) (B)
OH

(C) CH3 (D) CH3

OH HO

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

47. Choose the major product for the following elimination reaction.

CH3

H3C CH CH2 CH CH3 HO-

H H H
H3 C
(A) (B)
C C CH3 C C CH3
CH CH
H3C H
CH3 CH3

H3C
(C) CH3 (D)
H3CH2C H
CH CH2
C C C C
H3 C
H CH3
H H

[1]

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School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120W2: Chemical Reactivity
October 2019 Main Examination

48. Ethyl methanoate, also known as ethyl formate, is a sweet-smelling ester used
as a flavourant. Which of the following is the best method for preparing ethyl
methanoate shown below?
O

H O

Ethyl methanoate

(A) +
H H CH3CH2OH

O
(B) + CH3CH2OH
H CH2CH3

O
(C)
H H + CH3CH2Cl

O
(D)
+ CH3CH2OH
H Cl

[1]

THE END [60 MARKS]

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