FACULTY OF SCIENCE
DEPARTMENT OF CHEMICAL SCIENCES
B Eng Tech in Engineering Metallurgy / Extraction Metallurgy
MODULE
CAMPUS
CETM1A1
DFC
PAPER 2
DATE: 2022
ASSESSOR
Dr. MC FOTSING
INTERNAL MODERATOR
DR P. F. MSOMI
DURATION
180 MINUTES
TOTAL MARKS: 100
NUMBER OF PAGES: 9 PAGES, INCLUDING 4 ANNEXURES
INSTRUCTIONS:
ANSWER SECTION A ON THE MULTIPLE QUESTION ANSWER SECTION AND
SECTION B IN THE PROVIDED ANSWER SCRIPT.
CONSULT THE DATA SHEET AND THE PERIODIC TABLE FOR ALL
SUPPLEMENTARY INFORMATION.
CALCULATORS ARE PERMITTED (ONLY ONE PER STUDENT).
2/…
CETM1A1_Examination_Paper 2_2022
SECTION A
QUESTION 1
1.1
A separation process that depends on differing abilities of substances
to form gases is called __________.
A) filtration
B) solvation
C) distillation
D) chromatography
E) all the above are correct
1.2
Elements in Group 6A are known as the __________.
A) alkali metals
B) chalcogens
C) alkaline earth metals
D) halogens
E) noble gases
1.3
The ground-state electron configuration of the element __________ is
[Kr]5s14d5.
A) Nb
B) Mo
C) Cr
D) Mn
E) Tc
1.4
In general, as you go across a period in the periodic table from left to
right:
(1) the atomic radius __________;
(2) the electron affinity becomes __________ negative; and
(3) the first ionization energy __________.
A) decreases, decreasingly, increases
B) increases, increasingly, decreases
C) increases, increasingly, increases
D) decreases, increasingly, increases
E) decreases, increasingly, decreases
3/…
2
CETM1A1_Examination_Paper 2_2022
1.5
The Lewis structure of AsH3 shows __________ nonbonding electron
pair(s) on As.
A) 0
B) 1
C) 2
D) 3
E) This cannot be determined from the data given.
1.6
The total number of π bonds in the H–C≡C–C≡C–C≡N molecule is
__________.
A) 3
B) 4
C) 6
D) 9
E) 12
1.7
According to VSEPR theory, if there are three electron domains on a
central atom, they will be arranged such that the angles between the
domains are __________.
A) 90°
B) 180°
C) 109.5°
D) 360°
E) 120°
1.8
The combustion of ammonia in the presence of excess oxygen yields
NO2 and H2O:
4 NH3 (g) + 7 O2 (g) → 4 NO2 (g) + 6 H2O (g)
The combustion of 43.9 g of ammonia produces __________ g of NO2.
A) 2.58
B) 178
C) 119
D) 0.954
E) 43.9
4/…
3
CETM1A1_Examination_Paper 2_2022
1.9
Calcium carbide (CaC2) reacts with water to produce acetylene (C2H2):
CaC2 (s) + 2H2O (g) → Ca(OH)2 (s) + C2H2 (g)
Production of 13g of C2H2 requires consumption of __________ g of
H2O.
A) 4.5
B) 9.0
C) 18
D) 4.8 × 102
E) 4.8 × 10-2
1.10
The formula weight of silver chromate (Ag2CrO4) is __________ amu.
A) 159.87
B) 223.87
C) 331.73
D) 339.86
E) 175.87
1.11
Combining aqueous solutions of BaI2 and Na2SO4 affords a precipitate
of BaSO4. Which ion(s) is/are spectator ions in the reaction?
A) Ba2+ only
B) Na+ only
C) Ba2+ and SO42D) Na+ and I E) SO42- and I-
1.12
When aqueous solutions of AgNO3 and KI are mixed, AgI precipitates.
The balanced net ionic equation is __________.
A) Ag+ (aq) + I- (aq) → AgI (s)
B) Ag+ (aq) + NO3 - (aq) → AgNO3 (s)
C) Ag+ (aq) + NO3 - (aq) → AgNO3 (aq)
D) AgNO3 (aq) + KI (aq) → AgI (s) + KNO3 (aq)
E) AgNO3 (aq) + KI (aq) → AgI (s) + KNO3 (s)
5/…
4
CETM1A1_Examination_Paper 2_2022
1.13
The molarity of a solution prepared by diluting 43.72 mL of 1.005 M
aqueous K2Cr2O7 to 500 mL is __________.
A) 0.0879
B) 87.9
C) 0.0218
D) 0.0115
E) 0.870
1.14
A 31.5 mL aliquot of HNO3 (aq) of unknown concentration was titrated
with 0.0134 M NaOH (aq). It took 23.9 mL of the base to reach the
endpoint of the titration. The concentration (M) of the acid was
__________.
A) 0.0102
B) 0.0051
C) 0.0204
D) 0.227
E) 1.02
1.15
Identify the reducing agent in the following reaction?
14H+ + Cr2O72- + 3Ni → 3Ni2+ + 2Cr3+ + 7H2O
A) Ni
B) H+
C) Cr2O72D) H2O
E) Ni2+
1.16
What is the coefficient of Fe3+ when the following equation is
balanced?
CN- + Fe3+ → CNO- + Fe2+ (basic solution)
A) 1
B) 2
C) 3
D) 4
E) 5
1.17
On a phase diagram, the critical pressure is __________.
A) the pressure required to melt a solid
B) the pressure below which a substance is a solid at all temperatures
C) the pressure above which a substance is a liquid at all temperatures
D) the pressure at which a liquid change to a gas
E) the pressure required to liquefy a gas at its critical temperature
6/…
5
CETM1A1_Examination_Paper 2_2022
1.18
The equilibrium constant for the gas phase reaction
N2 (g) + 3H2 (g)
2NH3 (g)
is Keq = 4.34 × 10-3 at 300 °C. At equilibrium, __________.
A) products predominate
B) reactants predominate
C) roughly equal amounts of products and reactants are present
D) only products are present
E) only reactants are present
1.19
The value of Keq for the following reaction is 0.25:
SO2 (g) + NO2 (g)
SO3 (g) + NO (g)
The value of Keq at the same temperature for the reaction below is
__________.
2SO2 (g) + 2NO2 (g)
2SO3 (g) + 2NO (g)
A) 0.50
B) 0.062
C) 0.12
D) 0.25
E) 16
1.20
Which of the following is an exothermic process?
A) ice melting
B) water evaporating
C) boiling soup
D) condensation of water vapor
E) Ammonium thiocyanate and barium hydroxide are mixed at 25°C:
the temperature drops.
[20 x 2= 40]
7/…
6
CETM1A1_Examination_Paper 2_2022
SECTION B
QUESTION 2
2.1
Identify the specific element that corresponds to each of the following
electron configurations and indicate the number of unpaired electrons
for each
2.1.1
2.1.2
2.1.3
1s22s2
1s22s22p4
[Ar]4s13d5
(2)
(2)
(2)
2.2
Use Lewis symbols to represent the reaction that occurs between Ca
and F atoms.
(2)
2.3
Draw the Lewis structures for each of the following ions or molecules.
Identify those that do not obey the octet rule, and explain why they do
not:
2.3.1
2.3.2
2.3.3
SO32AlH3
SbF5
(2)
(2)
(2)
[14]
QUESTION 3
3.1
Determine the empirical formulas of the compounds with the following
composition by mass:
3.1.1
3.1.2
10.4 % C, 27.8 % S, and 61.7 % Cl
21.7 % C, 9.6 % O, and 68.7 % F
3.2
Hydrofluoric acid, HF (aq), cannot be stored in glass bottles because
compounds called silicates in the glass are attacked by the HF (aq).
Sodium silicate (Na2SiO3), for example reacts as follows:
Na2SiO3(s) + 8 HF(aq)
3.2.1
3.2.2
3.2.3
(3)
(3)
H2SiF6(aq) + 2 NaF(aq) + 3 H2O(l)
How many moles of HF are needed to react with 0.300 mol of
Na2SiO3?
(2)
How many grams of NaF form when 0.500 mol of HF reacts with
excess Na2SiO3?
(2)
How many grams of Na2SiO3 can react with 0.800 g of HF?
(2)
[12]
8/…
7
CETM1A1_Examination_Paper 2_2022
QUESTION 4
4.1
Will precipitation occur when the following solutions are mixed? If so,
write a balanced chemical equation for the reaction.
4.1.1
4.1.2
Na2CO3 and AgNO3
NaNO3 and NiSO4
4.2
Referring to figure 1 below, describe the phase changes and the
temperatures at which they occur when CO2 is heated from – 80 oC to
– 20 oC at
4.2.1
A constant pressure of 3 atm.
(4)
4.2.2
A constant pressure of 6 atm.
(4)
(4)
(4)
Figure 1: Phase diagram of CO2. Note that a linear scale is used to
represent temperature and a logarithmic scale to represent pressure.
[16]
9/…
8
CETM1A1_Examination_Paper 2_2022
QUESTION 5
5.1
At 1000 K, Kp = 1.85 for the reaction
SO3(g)
SO2(g) + 1/2 O2(g)
5.1.1
What is the value of Kp for the reaction below?
SO3(g)
5.1.2
(4)
SO2(g) + 1/2 O2(g)
What is the value of Kp for the reaction below?
(4)
2 SO3(g)
2 SO2(g) + O2(g)
5.1.3
What is the value of Kc for the reaction in question 5.1.2?
5.2
The following is known as the thermite reaction:
2 Al(s) + Fe2O3(s)
5.2.1
(5)
Al2O3(s) + 2 Fe(s)
This highly exothermic reaction is used for welding massive units, such
as propellers for large ships.
Using standard enthalpies of formation in Appendix C, calculate Ho
for this reaction.
(5)
[18]
FULL MARKS:100
TOTAL MARKS: 100
9
DATA INFORMATION
x=
− b  b 2 − 4ac
2a
Avogadro’s number: N = 6.02 x1023
0oC = 273.15 K
Standard pressure = 1 atm = 101.325 kPa = 760 mmHg = 760 torr = 1.01325 bar
R = 8.31451 L.kPa.K–1.mol–1
= 8.31451 x10–2 L.bar.K–1.mol–1
= 8.20578 x10–2 L.atm.K–1.mol–1
= 62.364 L.torr.K–1.mol–1
Equilibrium constants (Temperature = 25.0oC)
Kw = 1  10–14
Table 1: Thermodynamic Quantities for Selected Substances at 298.15 K(25 oC)
Substance
Aluminium
Al(s)
AlCl3(s)
Al2O3(s)
f 
 Gf 
(kJ/mol)
(kJ/mol)
S
(J/mol.K)
0
- 705.6
- 1669.8
0
- 630.0
- 1576.5
28.32
109.3
51.00
Iron
Fe(g)
Fe(s)
Fe2+(aq)
Fe3+(aq)
FeCl2(s)
FeCl3(s)
FeO(s)
Fe2O3(s)
Fe3O4(s)
FeS2(s)
415.5
0
- 87.86
-47.69
-341.8
-400
-271.9
-822.16
-1117.1
-171.5
369.8
0
-84.93
-10.54
-302.3
-334
-255.2
-740.98
-1014.2
-160.1
180.5
27.15
113.4
293.3
117.9
142.3
60.75
89.96
146.4
52.92
Oxygen
O(g)
O2(g)
O3(g)
OH-(aq)
H2O(g)
H2O(l)
H2O2(g)
H2O2(l)
247.5
0
142.3
-230.0
-241.82
-285.83
-136.10
-187.8
230.1
0
163.4
-157.3
-228.57
-237.13
-105.48
-120.4
161.0
205.0
237.6
10.7
188.83
69.91
232.9
109.6
Table 2: Solubility Guidelines for Common Ionic Compounds in Water
Soluble Ionic Compounds
Compounds containing
NO3CH3COOClBrISO42-
Insoluble Ionic Compounds
Compounds containing
S2CO32PO43OH-
Important Exceptions
None
None
Compounds of Ag+, Hg22+, and Pb2+
Compounds of Ag+, Hg22+, and Pb2+
Compounds of Ag+, Hg22+, and Pb2+
Compounds of Sr2+, Ba2+, Hg22+, and Pb2+
Important Exceptions
Compounds of NH4+, the alkali metal cations, Ca2+, Sr2+, and Ba2+
Compounds of NH4+ and the alkali metal cations
Compounds of NH4+ and the alkali metal cations
Compounds of NH4+, the alkali metal cations, Ca2+, Sr2+, and Ba2+
UNIVERSITY OF JOHANNESBURG
Department of Chemical Sciences
1
2
H
Atomic Number
He
1.0079
3
4
Li
4.0026
4.0026
5
Atomic Weight
Na
K
Ca
39.098
37
Rb
39
56
Cs
57
88
Fr
(223)
72
73
74
75
76
O
F
14.007
15.999
18.998
14
77
190.2
47
15
78
P
S
30.974
32.064
Pt
192.22
195.08
Cd
107.87
In
81
Hg
196.97
Sn
82
Tl
200.59
I
85
Po
207.2
208.98
(209)
226.03
68
69
70
71
(210)
Ac
227.03
58
59
Ce
Pr
140.12
90
60
Th
232.04
Nd
140.91
91
61
Pa
231.04
Pm
144.24
92
62
U
238.03
Sm
146.92
93
63
Np
237.05
Eu
150.36
94
64
Pu
(244)
Gd
151.97
95
65
Am
(234)
Tb
157.25
96
66
Cm
(247)
Dy
158.93
97
67
98
Bk
247
Ho
162.50
99
Cf
(251)
Er
164.93
100
Es
(252)
Tm
167.26
101
Fm
(257)
Yb
168.93
102
Md
(258)
Lu
173.04
174.97
103
No
(259)
131.29
86
At
204.38
Xe
126.90
89
Ra
83.80
54
127.60
84
Bi
Kr
79.904
Te
83
Pb
Br
53
121.75
39.948
36
78.96
Sb
Ar
35.453
Se
52
118.71
20.179
18
35
74.922
51
114.82
80
As
Ne
Cl
34
72.61
50
112.41
Au
33
Ge
49
17
28.086
69.723
48
79
Ir
Ga
16
Si
32
65.39
Ag
106.42
31
Zn
63.546
Pd
102.91
Os
186.2
46
30
Cu
58.69
Rh
101.07
Re
183.85
45
29
Ni
58.933
Ru
(98)
W
180.95
44
28
Co
55.847
Tc
95.94
Ta
178.49
43
27
Fe
54.938
Mo
92.906
Hf
138.91
42
26
Mn
51.996
Nb
91.224
La
137.33
41
25
Cr
50.942
Zr
88.906
Ba
132.91
40
24
V
47.88
Y
87.62
23
Ti
44.956
Sr
85.47
87
Sc
40.078
38
55
N
26.982
22
10
12.011
Al
21
9
C
24.305
20
8
10.811
13
Mg
22.990
7
B
9.0122
12
19
6
Be
6.941
11
He
2
Lr
(260)
Rn
(222)