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SCHOOL OF CHEMISTRY & PHYSICS
UNIVERSITY OF KWAZULU-NATAL, PIETERMARITZBURG CAMPUS
CHEM120/196: CHEMICAL REACTIVITY
OCTOBER 2014 MAIN EXAMINATION
Duration: 3 hours; 100 marks
Student No.
Seat Number:
Instructions:
• Part A consists of multiple choice questions and should be answered on the MCQ sheet provided
by making a cross over the most correct answer.
• Part B requires written answers and should be answered directly on this paper.
• Answer all questions.
• Non-programmable calculators are permitted for calculations, but show all working.
• There are 25 pages (including a Periodic Table and Data Sheet) in total; check that you have
them all.
Internal Examiners: Dr D. Reddy, Dr S. Sithebe and Dr B. Xulu (UKZN-PMB) Coordinator: Dr M. Akerman
Internal Moderators: Prof B. Martincigh, Dr V. Paideya and Dr K. Pruessner (UKZN-WVL)
Question
Internal
Marks
External
Marks
A
B1
B2
B3
Total
49
15
15
21
100
49
15
15
21
100
Rule 9 (1)(e) WARNING: CANDIDATES WILL BE DISQUALIFIED IF:
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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.
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October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
SECTION A - MULTIPLE CHOICE ANSWER SHEET
Choose the most correct answer for each of the multiple choice questions. Show your choice by
making a cross over the letter which corresponds to your answer, e.g. 1. X
a
b
c
d
1.
a
b
c
d
21.
a
b
c
d
2.
a
b
c
d
22.
a
b
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d
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a
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25.
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11.
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38.
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39.
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a
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d
Page 1 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
PART A – Multiple Choice Questions
Choose the most correct answer for each of the following multiple choice questions. Show your
answer on the sheet provided.
1.
What is the specific heat capacity of ethanol if 700 J of heat is required to raise the
temperature of an 80.0 g sample from 30.0 °C to 45.0 °C?
a)
0.194 J g–1 °C–1
b)
0.292 J g–1 °C–1
c)
0.583 J g–1 °C–1
d)
1.72 J g–1 °C–1
(1)
2.
Which of the following statements is false?
a)
The reaction vessel cools when an endothermic reaction occurs.
b)
An exothermic reaction is characterized by a negative value of ∆H.
c)
Heat is evolved when an exothermic reaction occurs.
d)
An endothermic reaction causes the surroundings to absorb heat.
(1)
3.
Consider the reaction below:
2NO 2 (g) → 2NO(g) + O 2 (g) ∆H = +114 kJ
What would be the enthalpy change if 23.0 g of NO 2 were reacted?
a)
114 kJ
b)
57.0 kJ
c)
28.5 kJ
d)
14.3 kJ
(2)
4.
Hydrogen gas can be prepared by reacting zinc granules with hydrochloric acid. Which of the
following factors will not increase the rate at which hydrogen gas is formed?
a)
Using zinc powder
b)
Increasing the concentration of the acid
c)
Increasing the volume of the acid
d)
Using hot acid
(1)
Page 2 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
5.
Given the following chemical equation:
7
2A + 2B → 3X + 4Y
we can express ∆H°rxn for this reaction in terms of the enthalpies of formation (∆H°f ) for each
of the reactants and products as being:
a)
b)
c)
d)
6.
∆H°rxn = ∆H°f (X) + ∆H°f (Y) − ∆H°f (A) − ∆H°f (B)
7
∆H°rxn = 3∆H°f (X) + 4∆H°f (Y) + 2∆H°f (A) + 2 ∆H°f (B)
7
∆H°rxn = 3∆H°f (X) + 4∆H°f (Y) − 2∆H°f (A) − 2 ∆H°f (B)
7
∆H°rxn = 2∆H°f (A) + 2 ∆H°f (B) − 3∆H°f (X) − 4∆H°f (Y)
(1)
A reaction has the experimental rate law: Rate = k[A]3. How will the rate change if the
concentration of A is tripled?
a)
It will increase by a factor of three.
b)
It will increase by a factor of nine.
c)
It will increase by a factor of twenty seven.
d)
It will remain the same.
(1)
7.
For the following reaction:
ClO–3 + 9I– + 6H+ → 3I–3 + Cl– + 3H2 O
the rate law is given as: Rate = k 1 [ClO 3 –][I–][H+]2
What are the units of the rate constant, k 1 ?
a)
mol L–1 s–1
b)
mol–1 L s
c)
mol–2 L2 s–1
d)
mol–3 L3 s–1
(1)
Page 3 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
8.
For the decomposition of 1 mole of nitrosyl chloride depicted below,
NOCl(g) → NO(g) + ½Cl 2 (g)
the enthalpy change, ∆H, is 38 kJ whilst the activation energy, E A , is 100 kJ. The activation
energy for the reverse reaction is:
a)
38 kJ
b)
62 kJ
c)
76 kJ
d)
138 kJ
(1)
9.
Which one of the following statements best describes the condition(s) needed for the
successful formation of a product according to the collision theory model?
a)
The collision must involve a sufficient amount of energy, provided from the motion
of the particles, to overcome the activation energy.
b)
The orientation of the particles has little or no effect on the formation of the
product.
c)
The relative orientation of the particles has an effect only if the kinetic energy of the
particles is below some minimum value.
d)
The energy of the incoming particles must be above a certain minimum value, and
the relative orientation of the particles must allow for the formation of new bonds in
the product.
(1)
10.
In the following reaction:
A(g) + B(g) ⇌ AB(g)
Equilibrium is reached in the reaction when:
a)
50% of the reactants have been used.
b)
All the reactants have been used.
c)
The products decompose as fast as they are formed.
d)
The reactants stop forming products.
(1)
Page 4 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
11.
Which of the following expressions correctly describes the equilibrium expression for the
reaction:
a)
b)
c)
d)
12.
KC =
4NH 3 (g) + 5O 2 (g) ⇌ 4NO(g) + 6H 2 O(g)
6[H2 O]+4[NO]
4[NH3 ]+5[O2 ]
[H O][NO]
3 ][O2 ]
2
KC = [NH
[NH3 ]4 [O2 ]5
KC = [H
2 O]
6 [NO]4
[H O]6 [NO]4
4
5
3 ] [O2 ]
2
KC = [NH
(1)
For the following equilibrium at 298 K:
N 2 O 4 (g) ⇌ 2NO 2 (g)
K P = 0.15
It was found that the partial pressure of N 2 O 4 is 3.7 × 10–2 atm at equilibrium. What is the
partial pressure of NO 2 at equilibrium?
a)
0.0016 atm
b)
0.0056 atm
c)
0.074 atm
d)
5.0 atm
(1)
13.
The equilibrium constant, K C , for the reaction shown below is 1.3 × 10–2 at 1000 K.
2NO(g) + Br 2 (g) ⇌ 2NOBr(g)
What is K P for the following reaction at the same temperature?
a)
1.58 × 10–4
b)
1.07
c)
76.9
d)
6.31 × 103
2NOBr(g) ⇌ 2NO(g) + Br 2 (g)
(2)
14.
Which of the following is the weakest acid?
a)
Ascorbic acid (K a = 8.0 x 10-5)
b)
Boric acid (K a = 5.8 x10-10)
c)
Butyric acid (K a = 1.5 x 10-5)
d)
Hydrocyanic acid (K a = 4.9 x10-10)
(1)
Page 5 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
15.
A solution in which the pOH is 5.3 could be described as:
a)
Slightly acidic
b)
Very basic
c)
Neutral
d)
Slightly basic
(1)
16.
When solid NaCN is added to water, the pH:
a)
remains at 7
b)
becomes greater than 7 because of hydrolysis of Na+
c)
becomes greater than 7 because of hydrolysis of CN–
d)
becomes less than 7 because of hydrolysis of CN–
(1)
17.
What is the mole fraction of ethanol, C 2 H 5 OH (molar mass = 46.068 g mol–1), in a methanol
solution that is 40.0 % methanol, CH 3 OH (molar mass = 32.042 g mol–1), by mass?
a)
0.49
b)
0.51
c)
0.56
d)
0.60
(1)
18.
Which of the following has the highest vapour pressure at room temperature?
a)
Ethylene glycol, b.p. = 198 oC
b)
Ethanol, b.p. = 78 oC
c)
Benzene, b.p. = 80 oC
d)
Carbon disulphide, b.p. = 46 oC
(1)
19.
Calculate the molar solubility of Ag 3 AsO 4 (K sp = 6 x 10–23)
a)
1.3 × 10–8 M
b)
1.2 × 10–6 M
c)
9.0 × 10–7 M
d)
1.8 × 10–8 M
(2)
Page 6 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
20.
For the balanced equation:
8H+ (aq) + 5Fe2+ (aq) + MnO 4 - (aq) → 5Fe3+ (aq) + Mn2+ (aq) + 4H 2 O (ℓ)
a)
Fe2+ (aq) is an oxidising agent
b)
H+ (aq) undergoes oxidation
c)
Fe2+ (aq) undergoes oxidation
d)
H+ (aq) is an oxidising agent
(1)
21.
What is the pH of a 0.20 M HA solution (K a = 1.0 x 10–6) that contains 0.40 M NaA?
a)
3.15
b)
3.35
c)
5.70
d)
6.30
(2)
22.
What is the pH after a titration when 20.0 mL of 0.0150 M KOH has been added to 35.0 mL
of 0.0100 M HCl?
a)
2.86
b)
2.92
c)
3.04
d)
3.18
(2)
23.
Which one of the following mixtures will be a buffer when dissolve in a litre of water?
a)
0.1 mol Ba(OH) 2 and 0.2 mol HCl
b)
0.4 mol NH 3 and 0.4 mol HCl
c)
0.2 mol CH 3 COOH and 0.1 mol NaOH
d)
0.2 mol HBr and 0.1 mol NaOH
(1)
Page 7 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
24.
In the voltaic cell which is represented as:
Cd│Cd2+││(Pt) Fe3+│Fe2+
The electron flow will be from
a)
Pt to Cd2+
b)
Fe2+ to Cd2+
c)
Cd2+ to Fe2+
d)
Cd to Fe3+
(1)
25.
Calculate Eo for the cell reaction:
2Cr(s) + 3Sn4+(aq) → 3Sn2+(aq) + 2Cr3+(aq)
Given: Cr3+(aq) + 3e → Cr(s)
Eo = -0.74 V
Sn4+(aq) + 2e → Sn2+(aq)
a)
1.93 V
b)
0.89 V
c)
0.59 V
d)
–0.59 V
Eo = 0.15 V
(1)
26.
Which of the following pairs of compounds are the products of the ozonolysis of
(Z)-2,3-diethylhex-2-ene?
H
a)
O
and
O
b)
O
and
O
H
c)
d)
O
and
O
O
and
O
(2)
Page 8 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
27.
Which of the following compounds contain a nitrile, amine and ketone functional groups?
O
CN
O
CN
O
O
NH2
CN
H
NH2
NH2
NH2
A
B
a)
A, B and D only
b)
B only
c)
D only
d)
A only
C
D
(2)
28.
Which of the following compounds have an S-configuration?
I
OH
C
C
H
a)
A and B
b)
B and C
c)
A and C
d)
A, B and C
F
COOH
H2N
C
COOH
Br
CH3
A
B
H3C
COOH
NH2
C
(2)
29.
What is the IUPAC systematic name of the following compound?
NH2
a)
5-aminohexan-3-ol
b)
4-hydroxyhexan-2-amine
c)
2-aminohexan-4-ol
d)
3-hydroxyhexan-5-amine
OH
(2)
Page 9 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
30.
What type of compound is formed when a 1° alcohol reacts with H 2 CrO 4 ?
a)
Alkene
b)
Carboxylic acid
c)
Aldehyde
d)
Ketone
(1)
31.
Which of the following statement is true for S N 2 reaction mechanism?
a)
The fastest reaction will occur with a tertiary alkyl halide.
b)
The mechanism is a two-step process.
c)
For a chiral starting material, the reaction occur with inversion of configuration.
d)
The rate of the reaction is dependent on the concentration of haloalkane only.
(1)
32.
The following is an example of which type of reaction?
OH
a)
Deoxygenation
b)
Hydrolysis
c)
Dehydration
d)
Hydrogenation
(1)
33.
The following is an example of which type of reaction?
CH3
+ Cl
Cl
a)
Nucleophilic substitution reaction
b)
Electrophilic addition reaction
c)
Free radical reaction
d)
Elimination reaction
CH3Cl
+ Cl
(1)
Page 10 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
34.
Which of the following is the most stable conformation considering a rotation about the
C 2 -C 3 bond in the following structure?
SH
2
1
3
4
Cl
Cl
H
Cl
H
H
H
a)
A
b)
B
c)
C
d)
D
H
H
H
Cl
H
Cl
H
SH
SH
SH
SH
A
B
C
D
(2)
35.
Is the carbon indicated by an asterisk in the structure below primary (1°), secondary (2°),
tertiary (3°) or quaternary (4°).
*
a)
1°
b)
2°
c)
3°
d)
4°
(1)
36.
Which of the following statements about hydrocarbons is false?
a)
Cis-1,2-dimethylcyclobutane is less stable than trans-1,2-dimethylcyclobutane.
b)
Alkanes are produced by hydrogenation of alkenes
c)
The smallest alkane which has constitutional isomer has four carbon atoms.
d)
Pentane is more reactive than 1-pentene.
(1)
Page 11 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
37.
The carbon, indicated by the asterisk in the structure below, exhibits which type of
hybridization?
O
*
a)
sp
b)
sp2
c)
sp3
d)
sp3d
(1)
38.
Which of the following compound/s has/have an asymmetric carbon?
H
O
NH2
H
Cl
A
a)
A and B
b)
B and C
c)
A and C
d)
B only
B
C
(2)
39.
The following is an example of what type of reaction?
OH
a)
Nucleophilic substitution
b)
Electrophilic addition
c)
Elimination
d)
Dehydration
(1)
[50]
Page 12 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
PART B – Written Answer Questions
Answer the following questions directly on the question paper in the space provided. Students are
requested to write neatly and clearly to ensure accurate marking.
QUESTION B1
a)
A piece of titanium with a mass of 20.8 g is heated to 99.5 °C and then dropped into a
coffee-cup calorimeter containing 75.0 g of water at 21.7 °C. When thermal equilibrium is
reached, the final temperature of the mixture is 24.3 °C. Given that C P [H 2 O(ℓ)] =
4.18 J g–1 °C–1, determine the specific heat capacity of titanium.
(4)
Page 13 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
b)
The equation for the formation of 1.0 mol of strontium carbonate from its elements in their
standard states is given as:
3
Sr(s) + C(s) + 2O2 (g) → SrCO3 (s)
Given the following information:
Sr(s) + ½O 2 (g) → SrO(s)
∆ f H° = –592 kJ mol-1
SrO(s) + CO 2 (g) → SrCO 3 (s)
∆H rxn = –234 kJ mol
C(graphite) + O 2 (g) → CO 2 (g)
∆ f H° = –394 kJ mol-1
-1
Calculate the enthalpy of formation, ∆ f H°, for SrCO 3 (s).
(3)
Page 14 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
c)
The following reaction:
2NO(g) + 2H 2 (g) ⇌ N 2 (g) + 2H 2 O(g)
was studied at 904 °C, and the data collected into the table below:
[NO]
[H 2 ]
Rate of Appearance of N 2
(mol L-1 s-1)
1
0.420
0.122
0.136
2
0.210
0.122
0.0339
3
0.210
0.244
0.0678
4
0.105
0.488
0.0339
Experiment
i)
Reactant Concentration (mol L-1)
Determine the order with respect to each reactant and write down the rate law for the
reaction.
(3)
Page 15 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
ii)
Calculate the rate constant for the reaction. Include the correct units.
(2)
d)
Hydrogen chloride reacts with oxygen at 400 °C as follows:
4HCl(g) + O 2 (g) + heat ⇌ 2Cl 2 (g) + 2H 2 O(g)
Using Le Chatelier’s principle explain how the following changes will affect the
concentration of Cl 2 (g).
i)
The temperature is increased.
(1½)
ii)
The volume of the reaction vessel is increased.
(1½)
[15]
Page 16 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
QUESTION B2
a)
When 10.0 mL of 0.0010 M Pb(NO 3 ) 2 is reacted with 5.0 mL of 0.015 M HCl, will PbCl 2
precipitate from solution? (K sp (PbCl 2 ) = 1.7 × 10–5)
(3)
b)
The acid used in car batteries is 4.27 mol dm–3 aqueous sulfuric acid, which has a density of
1.25 g mL–1. What is the molality of the acid?
(4)
Page 17 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
c)
The freezing point of ethanol (C 2 H 5 OH) is –114.6 oC. The molal freezing point depression
constant for ethanol is 2.00 oC m–1. What is the freezing point (oC) of a solution prepared by
dissolving 50.0 g of glycerine (C 3 H 8 O 3 ) in 200.0 g of ethanol? Note: Glycerine is a nonelectrolyte.
(3)
d)
Given that HOCN has K a = 3.5 x 10-4, what is the [H+] of a solution that is 0.0100 M in HOCl
and 0.0300 M in NaOCl?
(2.5)
Page 18 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
How long (in seconds) must a current of 4.00 A be applied to a solution of Cu2+ ions to
produce 2.0 grams of copper metal?
e)
(2.5)
[15]
QUESTION B3
a)
Give the IUPAC systematic names of the following compounds.
NH2
O
a)
N
OH
(1.5)
F
b)
O
O
OCH3
(1.5)
Page 19 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
b)
Draw the structural formula of cyclopropyl propyl ether.
(1)
c)
Arrange the following carbocations in order of increasing stability. Explain your answer in
full.
A
B
C
(3)
Page 20 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
d)
Arrange the following compounds in order of increasing acidity. Explain your answer.
CH 3 CH 2 OH
F 3 CCOOH
Cl 3 CCOOH
(3)
e)
Consider the following dehydration reaction. Give a detailed mechanism (using curly arrows)
for the reaction. Clearly label all intermediate(s) and product(s) that are formed.
OH
H2SO4
Heat
(4)
Page 21 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
f.
Draw a detailed mechanism for the following nucleophilic addition reaction. Clearly indicate
the major and the minor product(s) that will be formed.
HBr
(4)
Page 22 of 25
October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
g.
Provide the missing reagents, reactants or products (A-D) for the following reactions.
Br2
A =
a.
CH2Cl2
B =
B =
b.
OH
O
Lindlar catalyst
c.
C =
O
d.
OH
+
D
O
D=
(2)
[20]
~END~
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October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
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October 2014 Main Examination Session, CHEM120/196: Chemical Reactivity, UKZN, PMB
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