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DEPARTMENT OF CHEMISTRY
Faculty of Natural and Agricultural Sciences
Fakulteit Natuur- en Landbouwetenskappe
Lefapha la Disaense tša Tlhago le Tomo
CHM 171
Final Examination
2019
Surname
Initials
Signature
Student Number
Date: 7 June 2019
Examiners: Dr N Nombona
Time: 3 hours
Mrs AC Botha
Dr MDM Molefe
of
Marks: 100
Pages: 14
External Examiner: Dr PB Ramatsetse
RESULTS
Question
Question 1
Question 2
©

Examiner
19
22
19
Subtotal A
60
Subtotal B
40
TOTAL:
100
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INSTRUCTIONS
All answers (calculations, sketches, and diagrams) must be given in black or blue ink.
No correction ink allowed.
All calculations must be shown in full.
Information pages are attached (pages 13 - 14).
The thermodynamic data, reduction potentials and solubility rules are on page 13.
Only the information pages may be carefully removed.
Use the back of the page if you need more space to answer a question. Clearly indicate this action in
your answer.
You may use the molecular model kit.
Un







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B
Question 3
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A
Marks
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Section
STUDENT NUMBER
SECTION A
[60]
[19]
Question 1
1.1.
SECTION A
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STUDENT NUMBER
Scientists discovered a new class of black holes with masses 100 to 10000 times the mass of our sun,
but occupying less space than our moon. Suppose that one of these black holes has a mass of
1.0 × 10 suns and a radius equal to one half the radius of our moon. The radius of our sun is
7.0 × 10 km with an average density of 1.4 × 10 kg.m-3. The diameter of the moon is
2.16 × 10 miles. Given the provided, what is the density of the black hole in g.cm-3?
[7]
/
]
Draw the Lewis dot structure for
. The formal charge of bromine (the central atom) in the
structure must be zero. Use a different symbol for the electrons of each element.
[2]
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1.2.1
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[Answer: 9.15 × 10
CHM 171
Final Examination
2/14
*Answers given in library copy only for calculation type questions
© University of Pretoria
2019
STUDENT NUMBER
STUDENT NUMBER
Draw the Lewis 3-D Lewis line structure for
from your dot structure above. Show all lone
pair electrons (also on the terminal atoms). Clearly indicate the bond angles and the dipole
moment for the molecule (if applicable). Include all lone pairs.
[2]
1.2.3
What is the electron pair geometry of this ion?
1.2.4
What is the molecular geometry of this ion?
1.3.1
Use sulphur and oxygen to construct the most likely polyatomic anion with a trigonal pyramidal
molecular geometry. Draw the 3D-Lewis line structure for this molecule.
[3]
1.3.2
Draw all the resonance forms for this anion using Lewis line structures.
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1.2.2
[1]
[2]
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[1]
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1.3.3
What is the bond order of the S-O bonds in this anion?
CHM 171
Final Examination
[Answer: 1]
3/14
*Answers given in library copy only for calculation type questions
[1]
© University of Pretoria
2019
STUDENT NUMBER
[22]
Question 2
2.1
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STUDENT NUMBER
Which one of the following has the most oxygen atoms? Show your calculations.
(A) 0.0100
potassium chromate
(B) 2.4088 × 10 molecules of tetraphosphorus decoxide
(C) 1.612
magnesium oxide
[4]
2.2.1
Consider the combustion of methylhydrazine (
), a liquid rocket fuel:
( )+5 ( )→2 ( )+2
( )+6
()
2
What mass of
will be produced if 6.945 of
is added to 5.545 g of
calorimeter at 25.00℃ and allowed to react. Assume a 100% yield.
[5]
©
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[Answer: 3.821 ]
in a bomb
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2.2
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of
[Answer: 0.0400 mol; 0.004000 mol; 0.00004000 mol → ( )]
CHM 171
Final Examination
4/14
*Answers given in library copy only for calculation type questions
© University of Pretoria
2019
STUDENT NUMBER
The calorimeter has a heat capacity of 4.279 / and contains 840.0 water. The temperature
rises to 39.50℃ as a result of the reaction above. What is the enthalpy of formation of
methylhydrazine? Assume that the heat generated by the reaction is also the reaction enthalpy.
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2.2.2
STUDENT NUMBER
[7]
/
]
2.3
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of
[Answer: −2.55 × 10
Tartaric acid is a diprotic acid and one of the components in effervescent salts. The amount of the
acid in the salt is determined by volumetric analysis by reacting it with sodium hydroxide:
)+2
(
si
(
)→
(
)+2
()
©
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[Answer: 75.0%]
er
A 2.561 sample of the salt is dissolved to make 250.0
solution.
20.0
of this solution is diluted to 100.0
.
What is the mass percentage of tartaric acid in the salt sample if 16.25
of 0.0315 M
is
required to neutralise 25.00
of the dilute solution? Assume that none of the other compounds
in the salt react with
.
[6]
CHM 171
Final Examination
5/14
*Answers given in library copy only for calculation type questions
© University of Pretoria
2019
STUDENT NUMBER
[19]
Question 3
3.1
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STUDENT NUMBER
For the following reaction:
2KClO3(s) → 2KCl(s) + 3O2(g)
a) Calculate ΔH° and ΔS°
b) Is the reaction spontaneous at 25 °C?
c) Is the reaction entropy or enthaply driven ?
d) At what temperatures will the reaction be non-spontaneous?
[5]
; 494.19 /
(b) Yes, ∆
° = −225.382
(c) Both (d) Spontaneous at all T]
Calculate the standard free energy change (ΔG°, in kJ) at 25 °C for the following reaction.
( )→3
( )+8
( )+2 ( )+4
3 ( )+2
()
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[Answer: (a) −78.04
]
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[Answer: −360
[4]
CHM 171
Final Examination
6/14
*Answers given in library copy only for calculation type questions
© University of Pretoria
2019
STUDENT NUMBER
A galvanic cell consists of a tin electrode, which is in a 0.180 M solution of tin(II) nitrate and an
aluminium electrode which is in a 0.0150 M solution of aluminium nitrate.
These two half-cells are connected with a salt bridge consisting of a potassium nitrate solution, as well
as with an external conductor including a voltmeter. The temperature is 25.0C. Write the halfreactions, balanced cell reaction and calculate the cell potential of this cell.
[6]
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3.3
STUDENT NUMBER
When an aqueous solution of cupper (II) sulfate, CuSO4, is electrolysed, copper metal is deposited. If
a constant current was passed for 5.00 h and 404 mg of copper metal was deposited, what was the
current?
[4]
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[Answer: 1.53 ]
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[Answer: 0.0681 ]
CHM 171
Final Examination
7/14
*Answers given in library copy only for calculation type questions
© University of Pretoria
2019
STUDENT NUMBER
STUDENT NUMBER
1.
2.
3.
4.
5.
[40]
SECTION B
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SECTION B
INSTRUCTIONS
Answer the following questions on this paper and then transfer your answer to the computer answer sheet.
Use only side 2 of the answer sheet.
Only one answer per question is allowed.
No marks are considered for unclear answers. It is your responsibility to ensure that the answer sheet is readable by the
optical mark reader. All instructions are provided on the answer sheet.
The allocation of marks per question may vary, but is indicated at each question.
Question 1
Question 1
Mark option H of Question 1 on your computer answer sheet. This is for control purposes only and ensures that you
use Side 2 of the answer sheet.
[1]
Question 2
(A)
15 protons, 16 neutons, 12 electrons
(B)
16 protons, 15 neutons, 18 electrons
(C)
15 protons, 16 neutons, 18 electrons
(D) 12 protons, 19 neutons, 15 electrons
15 protons, 16 neutons, 15 electrons
(F)
15 protons, 18 neutons, 12 electrons
ty
(E)
?
of
How many protons, neutons and electrons are there in the ion
Question 2
[2]
Question 3
Question 3
The atomic weight of Ga is 69.72 amu. There are only two naturally ccuring isotopes of gallium: 69Ga, with a mass of 69.0
15%
(B)
30%
(C)
40%
(D) 50%
(E)
65%
(F)
80%
iv
Question 4
er
(A)
si
amu and 71Ga with a mass of 71.0 amu. The natural abundance of the 69Ga isotope is approximately:
[3]
Question 4
A sample of metallic element X, weighing 4.135 g, combines with 0.58 L of Cl2 at normal pressure and 20.0 °C to form
the metal chloride with the formula XCl. is 2.948 g/L, what is the identity of X? If the density of Cl2 gas under these
conditions
Kr
(B)
Sr
(C)
Y
Un
(A)
(D) Br
Rb
(F)
Se
©
(E)
CHM 171
Final Examination
8/14
*Answers given in library copy only for calculation type questions
© University of Pretoria
2019
STUDENT NUMBER
STUDENT NUMBER
[2]
Question 5
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Question 5
Selenium has an oxoacid, H2SeO4, called selenic acid. What is the formula and name of the corresponding ion?
(A)
SeO4¯, selenic ion
(B)
HSeO42¯, selenate ion
(C)
HSeO4¯, selenite ion
(D)
SeO42-, selenate ion
(E)
HSeO42+, selenate ion
(F)
SeO4¯, selenite ion
(G)
HSeO4¯, selenic ion
(H)
SeO42-, selenic ion
[3]
Question 6
Question 6
In the Balmer series of spectral lines for the hydrogen atom (
line with the highest energy?
(A)
1.368 × 10
m
(B)
1.875 × 10
m
(C)
4.091 × 10 m
= 6 and
(D) 1.875 × 10 m
(E)
4.091 × 10
m
(F)
1.368 × 10
m
= 2), what is the frequency of the
of
[2]
Question 7
Question 7
From the following set of quantum numbers, which best describes the electron that will be given off (or lost) when
nickel forms the Ni+ cation.
n=4
ℓ=1
mℓ = ‒1
ms = + ½
(B)
n=3
ℓ=2
mℓ = ‒3
ms = + ½
(C)
n=4
ℓ=3
mℓ = ‒1
ms = + ½
(D) n = 4
ℓ=2
mℓ = ‒3
(E)
n=3
ℓ=1
mℓ = ‒1
(F)
n=4
ℓ=0
mℓ = 0
ms = + ½
ms = + ½
ms = + ½
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Question 8
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(A)
[2]
Question 8
(A)
<
<
(B)
(D)
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
Un
(E)
<
<
iv
(C)
er
What is the correct rank of these ions according to increasing atomic radius?
©
(F)
<
CHM 171
Final Examination
<
,
,
,
,
9/14
*Answers given in library copy only for calculation type questions
© University of Pretoria
2019
STUDENT NUMBER
STUDENT NUMBER
What is the electron configuration of oxygen in OF2?
(A)
1s22s22p1
(B)
1s22s22p2
(C)
1s22s22p3
(D) 1s22s22p4
(E)
1s22s22p5
(F)
1s22s22p6
[2]
Question 10
Which of the following reactions is/are gas-forming reactions?
( )+
( )→
( )+ ( )→
( ) ( )+
( )→
( )+(
) ( )→
( )+2
( )→
(A)
(I) only
(B)
(II) only
(E)
(V) only
(F)
(I) & (II)
(I)
(I) & (V)
(C)
(III) only
(D)
(IV) only
(G)
(I) & (IV)
(H)
(II) & (V)
[2]
of a 0.0050
solution of strontium hydroxide?
2.30
(B)
11.70
(C)
2.00
(D)
12.00
(E)
4.00
(F)
10.00
[3]
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si
(A)
Question 7
Question 7
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Question 11
What is the
Question 10
of
(I)
(II)
(III)
(IV)
(V)
Question 9
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[2]
Question 9
Question 12
What is the mass percentage of carbon in
if combustion of a 0.8691 g sample produces 0.7765 g
known that oxygen makes up 10.580% of the mass of the sample.
79.42%
(C)
74.42%
10.00%
(D)
20.58%
84.71%
(F)
40.27%
©
Un
(E)
(B)
iv
(A)
and it is
CHM 171
Final Examination
10/14
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© University of Pretoria
2019
STUDENT NUMBER
STUDENT NUMBER
Question 13
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[3]
Question 13
What is the concentration of the chlorate ions in solution after the following three solutions are mixed?
25.00
25.00
50.00
of 0.2500
of 0.2500
of 0.0500
lead(II) nitrate
ammonium chlorate
zinc chlorate
(A) 0.006250
(B) 0.1125
(C) 0.1875
(D) 2.019
(E) 0.3125
(F) 0.4167
[3]
Question 14
What is the percent yield if 2.00 ethanol (
0.1400
hydrogen gas are allowed to react.
Question 14
, 32.042 ) is produced when 0.0750
( )+2
( )→
carbon monoxide and
()
(A) 44.6%
of
(B) 70.0%
(C) 83.2%
(D) 41.6%
(E) 89.2%
ty
(F) 66.9%
[2]
Question 15
Question 15
si
How many water molecules are there in the balanced equation for the following redox half-reaction which takes place
( )→
( )
in basic medium:
1 on the left
(B)
(C)
2 on the left
(D)
2 on the right
(E)
4 on the left
(F)
5 on the right
Question 16
1 on the right
er
(A)
[2]
Question 16
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Under what conditions will a reaction with the following profile be spontaneous?
(A)
ΔH°>0 and
>0
©
(D) ΔH°>0 and ΔS° >0
CHM 171
Final Examination
(B) ΔH°<0 and ΔS° <0
(C)
ΔH°>0 and ΔS° <0
(E) ΔH°>0 and
(F)
ΔH°<0 and
>0
11/14
*Answers given in library copy only for calculation type questions
<0
© University of Pretoria
2019
STUDENT NUMBER
[2]
Question 17
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STUDENT NUMBER
Question 17
A certain galvanic cell contains a standard hydrogen half-cell which acts as the cathode. Which of the following
statements about the hydrogen half-cell is true?
(A)
The pH increases
(D)
Hydrogen gas flows through the cell unchanged
(B)
Hydrogen gas acts as a reactant
(E)
Hydrogen gas is the oxidizing agent
(C)
Hydride ion forms
(F)
None if the above are true
The next TWO questions refer to the following:
A galvanic cell consists of a cadmium electrode in a 1.0 M CdSO4(aq) solution, and a nickel electrode in a 1.0 M
NiSO4(aq) solution at 25 °C. The salt bridge consists of a solution of NaNO3(aq).
[2]
Question 18
Question 18
The species that is reduced, and the half-reaction that increases in concentration of its own metal cation, respectively,
are?
Ni2+(aq); Ni half-cell
(D) Cd2+(aq); Cd half-cell
(B)
Ni(s); Ni half-cell
(E) Cd(s); Cd half-cell
(C)
Na+(aq); NaNO3 half-cell
(F) Ni2+(aq); Cd half-cell
of
(A)
[2]
Question 19
Question 19
The electrode which decreases in mass, and the direction of flow of NO3¯(aq), respectively, are?
Ni(s); to the Ni half-cell
(D) Cd(s); to the Ni half-cell
(B)
Ni(s); to the Cd half-cell
(E) Cd(aq); to the Ni half-cell
(C)
Cd(s); to the Cd half-cell
(F) Ni(aq); to the Cd half-cell
si
ty
(A)
©
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Check that you have coded answers 1 to 19 on Side 2 of the answer sheet
CHM 171
Final Examination
12/14
*Answers given in library copy only for calculation type questions
© University of Pretoria
2019
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General solubility guidelines
SOLUBLE COMPOUNDS
Almost all salts of
Salts containing
chloride
fluoride
bromide
iodide
Almost all salts of
sodium
potassium
ammonium
Salts of
nitrate
chlorate
perchlorate
acetate
Exceptions: None
Exceptions
(not soluble in
combination with)
silver(I)
mercury(I)
lead(II)
INSOLUBLE COMPOUNDS
Most salts of
Most metal
hydroxides and
carbonate
oxides
phosphate
oxalate
chromate
sulphide
Salts of
sulphate
Exceptions
(not soluble in
combination with)
magnesium
calcium
strontium
barium
lead(II)
Exceptions
(not soluble in
combination with)
calcium
strontium
barium
lead(II)
sliver(I)
Exceptions
(soluble in
combination with)
ammonium
alkali metal cations
Exceptions
(soluble in
combination with)
alkali metal cations
strontium
barium
Thermodynamic values at 25℃
You may assume that the ∆ ° and ° values are independent of temperature
69.95
∆ °
( /
)
−228.59
O2 (g)
( )
−393.5
213.6
−394.4
KCl (s)
−436.75
82.59
−409.14
C2H5OH (l)
−277.69
160.7
−174.9
CO2 (g)
−393.51
213.74
−394.4
KClO3 (s)
−397.73
143.1
−296.25
( / ∙
°
)
Substance
(
∆ °
/
)
( / ∙
°
)
(
∆ °
/
)
205.07
of
()
∆ °
( /
)
−285.83
Substance
Standard reduction potentials in aqueous solution at 25℃
(
⇌
)+8
(
)+5
( )+4
(
)+4
( )+2
)+4
(
)+
(
)+
(
)+3
)
⇌
2
()
⇌
2
(
+2.87
()
+1.52
+1.360
+1.229
)
+1.08
⇌
( )+2
⇌
( )
⇌
(
)
+0.771
(
)
+0.40
)+2
(
(
⇌
4
()
+0.96
+0.80
( )
+0.34
⇌
( )
0.00
)+2
⇌
( )
−0.14
)+3
⇌
( )
− 1.66
(
)+2
⇌
( )
−0.25
(
)+2
⇌
( )
−0.403
(
)+2
⇌
( )
−0.44
(
)+2
⇌
( )
⇌
( )+2
⇌
( )
Un
iv
⇌
( )+2
(
)+4
(
(
2
(
2
)+2
( )+4
)
⇌
(
( )+2
(
⇌
er
(
2
si
( )+2
2
ty
( )+2
( )
)+
−0.763
(
)
−0.8277
−3.045
©
*Versus the standard hydrogen electrode
CHM 171
Final Examination
13/14
Information page
© University of Pretoria
2019
Key
1
Atomic number
Element symbol
183.85 Relative Atomic mass
1.7 Electronegativity
74
H
2
W
1.0079
2.1
3
4
Li
Be
6.941
9.0122
1.0
1.5
11
12
Na
Mg
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THE PERIODIC TABLE OF THE ELEMENTS
He
4.0026
5
6
7
8
9
10
B
C
N
O
F
Ne
10.811
22.9898 24.3050
12.011 14.0067 15.9994 18.9984 20.1797
2.0
2.5
3.0
3.5
13
14
15
16
4.0
17
18
Al
Si
P
S
Cl
Ar
26.9815 28.0855 30.9738 32.066 35.4527 39.948
0.9
1.2
1.5
1.8
2.1
2.5
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
47.867 50.9415 52.9961 54.9380 55.847 58.9332 58.693
63.546
65.39
69.723
72.61
74.9216
78.96
79.904
83.80
1.9
1.6
1.6
1.8
2.0
2.4
2.8
39.0983 40.078 44.9559
0.8
1.0
1.3
1.5
1.6
1.6
1.5
1.8
1.9
1.8
3.0
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
Rb
Sr
Y
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
85.4678
87.62
88.9059
91.224 92.9064
95.94
(98)
101.07 102.906 106.42 107.868 112.411 114.82 118.710 121.757 127.60 126.905 131.29
0.8
1.0
1.2
1.4
1.6
1.8
1.9
2.2
2.2
2.2
1.9
1.7
1.7
1.8
1.9
2.1
55
56
57
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
Cs
Ba
La
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
(209)
(210)
(222)
2.0
2.2
132.905 137.327 138.906
0.7
178.49 180.948 183.85 186.207 190.23
0.9
192.22 195.084 196.967 200.59 204.383 207.20 208.980
1.3
1.5
1.7
1.9
2.2
2.2
2.2
2.4
1.9
1.8
1.9
1.9
87
88
89
104
105
106
107
108
109
110
111
112
114
116
Fr
Ra
Ac
Rf
Db
Sg
Bh
Hs
Mt
Ds
Rg
Cn
Fl
Lv
(261)
(262)
(263)
(262)
(265)
(266)
(271)
(272)
(285)
(223)
226.025 227.028
0.9
58
59
60
61
62
Ce
Pr
Nd
Pm
Sm
140.115 140.908 144.24
(145)
150.36 151.965 157.25 158.925 162.50 164.930 167.26 168.934 173.04 174.967
90
91
92
93
94
Th
Pa
U
Np
Pu
232.038 231.036 238.029 237.048
(244)
63
64
65
66
67
68
69
70
71
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
of
0.7
2.5
95
96
97
98
99
100
101
102
Am
Cm
Bk
Cf
Es
Fm
Md
No
103
Lr
(243)
(247)
(247)
(251)
(252)
(257)
(258)
(259)
(260)
Volume of a sphere = 
=ℎ
Δ = +
=
Δ
∆
=− ℎ
=
−
°=Σ ∆
∆ °=Σ
1
∆
ℎ
°=Σ ∆
= −log[
]
+
= 14
)−Σ ∆
°(
=
=−
)
°(
°(
°(
∙
iv
of/or ∙
Δ
°=Δ
Δ
=∆ °+
= ℱ
°=− ℱ °
° = −RT ln
∆
∆
)
)
= °−
)
) + ∆ °(
= °−
∆
ln
er
∆
ℎ = 6.626 × 10
∙
= 1.097 × 10
∙
= 2.998 × 10
= 6.022 × 10
ℱ = 9.6485 × 10 ∙
= 1.602 × 10
= 9.109 × 10
)−Σ
) = ∆ °(
∆ °(
Constants
)−Σ ∆
°(
°(
si
∆ =− ℎ
1
ty
Equations
0° = 273.15
∙
(H2O(ℓ)) = 4.184 ∙
∙
(H2O(s)) = 2.06 ∙
∙
(H2O(g)) = 1.92 ∙
(
) = 6.01 ∙
∆
(
) = 40.65 ∙
∆
°− Δ °
ln
ℱ
0.0257
°
=
0.0257
Gas constant, :
= 8.3145 ∙
ln
ln
(25°C)
(25° )
∙
Conversion Factors
Un
1 = 1.661 × 10
=1
1 = 10
1
= 1.000 × 10
1 =1
∙1
1
ℎ = 3.6 × 10
1
= 1.602 × 10–
1
ℎ = 2.54
1 = 12
ℎ
1
=3
1
= 0.62137
1
= 4.184
1 Å = 10
∙ ∙
=1 ∙ =1
1 = 0.2390
=1 ∙ =1
= 1.013 × 10
= 760
1
= 1.013 × 10 ∙
1
= 16
= 453.59
∙1
= 760
Equilibrium
©
At equilibrium:
= 0 and
=
( )+ ( )⇌ ( )+
( )+
( )
[ ] [ ]
of/or =
of/or =
[ ] [ ]
Liquids and solids are given a value of 1 unit in the and expressions
CHM 171
Final Examination
(
)+
(
)⇌
14/14
Information page
( )
For insoluble salts
( )⇌
( )+
=[
] [
]
(
© University of Pretoria
2019
)