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ICH402S - INTRODUCTION TO CHEMISTRY B - 2ND OPP SUPL - JAN 2023 |
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n Am I BI A u n IVE RS ITY
OF SCIEn CE Ano TECHn
FACULTY OF ENGINEERING AND THE BUILT ENVIRONMENT
lnSTEM
QUALIFICATION: INTRODUCTION TO SCIENCE, TECHNOLOGY, ENGINEERING AND MATHEMATICS
QUALIFICATION CODE: 04STEM
LEVEL: 4
COURSE CODE: ICH402S
COURSE NAME: INTRODUCTION TO CHEMISTRY B
SESSION:
DURATION:
JANUARY 2023
3 HOURS
PAPER:
N/A
MARKS:
100
SECOND OPPORTUNITY/SUPPLEMENTARY EXAMINATION PAPER
EXAMINER{S)
Ms Elvira van Wyk
Mr Victor Nwagbara
MODERATOR:
Dr Kayini Chigayo
INSTRUCTIONS
1. Answer all questions.
2. Write all the answers in ink.
3. No books, notes, correction fluid (Tippex) or cell phones allowed.
4. Pocket calculators are allowed.
5. You are not allowed to borrow or lend any equipment or stationary.
6. Periodic Table on page 9
THIS EXAMINATION PAPER CONSISTS OF 10 PAGES (Excluding this front page)
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Question 1
[10]
1.1 Chlorate(!) ions undergo the following reaction under aqueous conditions.
A series of experiments was carried out at different concentrations of Clo- and
NH3.
The table below shows the results obtained.
[Clo-] /mol
experiment
dm-3
[NH3]
/moldm- 3
initial rate
/moldm- 3 s-1
1
0.200
2
0.400
3
0.400
0.200
0.200
0.400
1.025
2.05
8.20
1.1.1 Use the data in the table to determine the order with respect to each reactant,
Clo- and NH3.
Show your reasoning.
(2)
11.2 Write the rate equation for this reaction.
(1)
1.1.3 Use the results of experiment 1 to calculate the rate constant, k, for this reaction.
Include the units of k.
(2)
1.2 In another experiment, the reaction between chlorate(!) ions and iodide ions in
aqueous alkali was investigated. A solution of iodide ions in aqueous alkali was
added to a largenexcess of chlorate(!) ions and W]was measured at regular
intervals.
1.2.1 Describe how the results of this experiment can be used to confirm that the reaction
is first-order with respect to [I]
(2)
1.2.2 A three-step mechanism for this reaction is shown.
Step 1 1 Clo-+ H20 -+ HCI O + OW
Step 2 1-+ HCIO -+ HIO + c1-
Use this mechanism to deduce the overall equation for this reaction.
(1)
1.2.3 In the three-step mechanism in 1.2.2, Identify a step that involves a redox reaction.
Explain your answer.
(2)
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Question 2
[14]
Entropy changes and free energy changes can be used to predict the feasibility of
processes.
2.1 Three processes are given below.
For each process, predict and explain whether the entropy change, fj,5, would be
positive or negative.
• The melting of iron.
• The reaction of magnesium with dilute sulfuric acid.
• The complete combustion of ethane: 2C2H5(g)+ 7O2(g) _. 4CO2(g)+ 6H2O(I) (3)
2.2 Ammonia can be oxidised as shown in the equation below.
= = At 450°C, /j,H -907 kJ moI- 1 and /j,G -1041 kJ moI- 1. Calculate the standard
entropy change, fj,5, in J K-1 moI- 1, for this reaction.
Show all your working.
(4)
2.3 A reaction is not feasible at low temperatures but is feasible at high temperatures.
Deduce the signs of /j,H and fj,5for the reaction and explain why the feasibility
changes with temperature.
(3)
2.4 The metal tungsten is obtained on a large scale from its main ore, wolframite.
Wolframite contains tungsten(VI) oxide, WO3.
Tungsten is extracted from wolframite by reduction with hydrogen:
WO3(s) + 3H2(g) -t W(s) + 3H2O(g)
/j,H = +115 kJmoI-1
Standard entropies are given in the table below.
Substance WO3(s)
s0 /JK-1moI-1
76
H2(g)
131
W(s)
33
H2O(g)
189
2.4.1 Calculate the free energy change, /j,G, in kJmoI-1, for this reation at 25°C.
(2)
2.4.2 Calculate the minimum temperature, in K, at which this reaction becomes feasible.
(Show your working)
(2)
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Question 3
[21]
This question is about acids, bases and buffers solutions.
3.1 Ethanoic acid, CH3COOH,and propanoic acid, C2HsCOOH,are weak Br¢nsted-Lowry
acids.
The acid dissociation constants, Ka,of the two acids are shown below.
Acid
Ka/mol dm-3
CH3COOH
C2HsCOOH
1.70 X 10-s
1.30 X 10-s
3.1.1 Explain the term weak acid.
(1)
3.1.2 Write the expression for the acid dissociation constant, Ka, of ethanoic acid.
(1)
3.1.3 Calculate the pH of a 2.85 x 10-2 mol dm- 3 solution of C2HsCOOH.
Give your answer to two decimal places.
(2)
3.1.4 Ethanoic acid is mixed with propanoic acid. An acid-base equilibrium is set up.
Copy and complete the equation for the equilibrium.
Label the conjugate acid-base pairs using the labels acid 1, base 1, acid 2, base 2.
C2HsCOOH+ CH3COOH -+ .................... + ...................
(2)
3.2 Barium hydroxide, Ba(OH)2, is a strong Br¢nsted-Lowry base.
A student prepares 250.0 cm3 of 0.1250 mol dm- 3 barium hydroxide.
3.2.1 Explain what is meant by the term Br¢nsted-Lowry base.
(1)
3.2.2 Calculate the mass of Ba(OH}2that the student would need to weigh to two decimal
places to prepare 250.0 cm3 of 0.1250 mol dm- 3 Ba(OH)2.
(3)
3.2.3 Calculate the pH of a 0.1250 mol dm- 3 solution of Ba(OH)2.
Give your answer to two decimal places.
(3)
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3.3 The student attempts to prepare a buffer solution by mixing 200 cm3 of
0.324 mol dm- 3C2HsCOOHwith 100 cm3 of the 0.1250 mol dm- 3Ba(OH}i prepared
in 3.2.
The equation for the reaction that takes place is shown below.
2C2HsCOOH(aq)+ Ba(OH)i(aq) -+ (C2HsCOO)iBa(aq)+ 2H2O(I)
Explain whether the student was successful in preparing a buffer solution.
Include all reasoning and any relevant calculations.
(3)
3.4 Blood contains a mixture of carbonic acid, H2CO3,and hydrogen carbonate ions,
HCO3-.
Explain how the carbonic acid-hydrogen carbonate mixture acts as a buffer.
In your answer include the equation for the equilibrium in this buffer solution and
explain how this equilibrium system is able to control blood pH
(5)
Question 4
[12]
4.1 20.0 cm3of 0.100 moldm- 3 NaOH were slowly added to a 10.0 cm3 sample of 0.100
moldm- 3 ethanoic acid, and the pH was measured throughout the addition.
4.1.1 Calculate the number of moles of NaOH remaining at the end of the addition.
(2)
4.1.2 Calculate the [OW] at the end of the addition.
(3)
4.1.3 Using the expression Kw=[W][OW] and your value in 4.1.2, calculate [W] and the
pH of the solution at the end of the addition.
(3)
4.2 Draw similar axes as below in your answer book, sketch how the pH will change
during the addition of a total of 20.0 cm3 of 0.100 mol dm- 3 NaOH. Mark clearly
where the endpoint occurs.
(3)
14....------,------,-----,--------,
pH
7-----+-------+----+--------1
o-----------------
0
5
10
15
20
volume NaOH added/ cm3
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4.3 From the following list of indicators, which one is most suitable for this titration
Indicator
pH
Malachite green
0-1
Thymol blue
1-2
Bromophenol blue
3-4
Phenolphthalein
9-10
(1)
Question 5
[17)
5.1.1 Define the term standard cell potential, E;ell·
(1)
The following incomplete diagram shows the apparatus that can be used to measure
the E;eufor a cell composed of the Fe3+/ Fe2+ and Ag+/ Ag half-cells.
A
B
5.1.2 Redraw and complete the diagram, labelling the components you add.
(1)
5.1.3 Identify the components A-D.
(4)
5.2.1 Use E0 values provided to write an equation for the cell reaction that takes place if
the two electrodes in 5.1.1 are connected by a wire and the circuit is completed.
(1)
Standard electrode potential and redox
potentials, E0 at 298 K {25 oC)
Ag+ + e- .==Ag
Fe3+ + e- .==Fe2+
Fe2+ + 2e- .==Fe
Fe3+ + 3e- .==Fe
Eo/v
+0.80
+0.77
-0.44
-0.04
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5.2.2 Another electrochemical cell was set up using 0.31 mol dm- 3 Ag+(aq) instead of the
standard Ag solution.
Use the Nernst equation, E = E0 + 0.059 log [Ag+(aq)], and the relevant E0 values to
calculate the new Eceliln this experiment.
(2)
5.3.1 Write an expression for the solubility product, Ksp,of PbCb.
(1)
5.3.2 Calculate the value of Ksp,including units.
(2)
5.4 The behaviour of Pbb and SnCb towards reducing agents are similar, but their
behaviour towards oxidising agents are very different.
Table of some electrode potentials
Half-reaction
Zn2+ + 2 e· Zn(s)
Fe2++ 2e· Fe(s)
Pb2+ + 2e· Pb
Sn2+ + 2e· Sn
2W + 2e · H2
Sn4++ 2e· Sn
21· + 2e· Ii
Ag++ e· Ag
Br2(I)+ 2e- 2Br·
2ci- + 2e· Cb
Pb4* + 2e· Pb2+
Electrode potential {V)
-0.76
-0.44
-0.13
-0.14
0.00
0.15
0.54
0.80
1.07
1.36
1.69
5.4.1 Illustrate this comparison by quoting and comparing relevant £0 values shown in the
table above for the two metals and their ions. Explain what the relative £0 values
mean in terms of the ease of oxidation or reduction of these compounds.
(3)
5.4.2 Writing a balanced molecular or ionic equation in each case, suggest a reagent to
carry out each of the following reactions.
Pb2+-+ Pb (s) and Sn4+-+ Sn2+
(2)
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Question 6
[21)
Allyl bromide, CH2=CHCH2Bri,s used in the production of polymers.
6.1 Part of the C=Cdouble bond in allyl bromide is called an-bond. Draw a labelled
diagram to show the formation of then-bond.
(2)
6.2 Allyl bromide is a member of a homologous series. Compounds in this series have
the same general formula
6.2.1 What is meant by the term homologous series?
(2)
6.2.2 What is the general formula of the homologous series that has allyl bromide as a
member?
(1)
6.2.3 Give the systematic name for allyl bromide.
(1)
6.3 Reaction mechanisms use curly arrow and can involve electrophiles and nucleophiles.
6.3.1 What does a curly arrow represent in mechanisms?
(1)
6.3.2 What is meant by the term nucleophile?
(1)
6.4 Allyl bromide, CH2=CHCH2Brr,eacts with bromine, Br2.
Outline the mechanis of this reaction.
Include curly arrows, relevant dipoles and the intermediate and final product(s).
(4)
6.5 This part of the question is about molecules with molecular formula (4Hs02.
6.5.1 Give the structural formulae of the pair of chain isomers with the formula (4Hs02
that are carboxylic acids.
(2)
6.5.2.1 Give the structural formulae of a pair of positional isomers with the formula (4Hs02
That are esters.
(2)
6.5.2.2 Give the reagents and conditions needed to produce one of your esters in 6.6.2.1 (2)
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6.5.3
The infra-red spectra of one of the esters and of another isomer, X, are shown.
X decolourises bromine water and is not an ester or an acid.
infra-red spectrum of the ester
Transmittance
50
0
4000
3000
2000
1500
1000
500
wavenumber/ cm- 1
infra-red spectrum of X
10
transmittance
50
0
4000
3000
2000
1500
1000
500
wavenumber/ cm-1
Explain the differences between these two spectra, with particular reference to the
peaks with wavenumbers above 1500 cm- 1.
Absorption frequencies are given on the last page of this paper.
(3)
Question 7
(5]
7.1 Write the equations for the following decay processes:
The beta decay of uranium -237
(1)
7.2 A chemist determines that a sample of petrified wood has a carbon-14 decay rate of
6.00 counts per minute per gram. What is the age of the piece of wood in years?
The decay rate of carbon-14 in fresh wood today is 13.6 counts per minute per gram,
and the half life of carbon-14 is 5730 years.
· (4)
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The Periodic Table of the Elements
1
2
3
4
5
6
7
0
1.0
4.0
H
He
(1)
(2)
Key
hydrogen
1
(13)
(14)
(15)
(16)
(17)
helium
2
6.9
Li
lithium
3
9.0
Be
belytlium
4
relative atomic mass
symbol
name
atomic (proton) number
10.8
12.0
14.0
16.0
19.0
20.2
B
C
N
0
F
Ne
boron
carbon nitrogen oxygen
fbmne
neon
5
6
7
8
9
10
23.0
24.3
Na
Mg
sodium
11
1111112Qnesium(3)
(4)
(5)
(6)
m (8)
27.0
Al
28.1
SI
31p.0
s32.1
35.5
Cl
39.9
Ar
(9)
(10) (11)
aluminium
(12)
1!'1
sllcon
1.4
phosplloRJB sulfur
1~
1R
chlorine
17
aigcn
1R
39.1
K
4c0a.1
45.0
Sc
47.9
Ti
50.9
V
52.0
Cr
54.9
55.8
Mn Fe
58.9
58.7
Co
Ni
6c3.u5
85A
Zn
69.7
Ga
72.8
Ge
74.9
As
79.0
Se
79.9
Br
83.8
Kr
potassium calcium scaooium titanium vanadium chromium manganese ircn
cabal!
nickel
copper
zinc
gallium germanium anienic selenium bronine krypton
\\J_
19
20
21
22
23
24
25
26
'IT
28
29
30
31
32
33
34
35
36
85.5
Rb
rubidium
37
87.8
Sr
strontium
3B
88y.9
yttrium
39
91.2
Zr
zlrconium
40
92.9
Nb
nicbium
41
98.0
[97] 101.1
Mo
Tc
Ru
molybdetun 18chnatium ruthenium
42
43
44
102.9
Rh
rhodium
45
106.4
Pd
paladlum
46
107.9
Ag
,silver
47
112.4
Cd
cadmium
48
114.8
In
lrdum
49
118.7
Sn
tin
50
121.8
Sb
antimony
51
127.6
Te
tellurium
52
126.9
I
iodine
53
131,3
Xe
xenon
54
132.9
Cs
caesun
55
137.3
Ba
bar1Lm
58
138.9
La*
lanthanum
51
178.5
Hf
hafnium
72
180.9
'Ill
tantalum
73
w 183.8
tungsten
74
186.2
Re
menlum
75
190.2
Os
osmium
76
192.2
Ir
Iridium
77
195.1
Pt
platinum
78
197.0
Au
gold
79
200.6
Hg
mercury
80
204.4
Tl
thalllum
81
207.2
Pb
lead
82
209.0
Bl
bismuth
83
[209]
Po
polonium
84
[210)
At
astatine
85
[222)
Rn
radon
86
[223)
Fr
francium
87
[226]
Ra
radium
88
[227] [267] [270) [269]
Act Rf Db Sg
actinium llltlllllfordl111d1u1bnlum
89
104
105 -106
1270]
Bh
bolv1um
107
[270]
Hs
hessium
1M
[278]
[281]
[281] [2851 [286]
Mt
Os
Rg
Cn
Nh
--··110-·· meltnerium
109
roertgenium copemlclum nlhcnlum
111
112
113
[289]
Fl
fferovlum
114
1M28c9)
[293]
Lv
rnoecovium livsnnorium
115
116
(294] (294]
Ts Og
teone861ne ogane660l1
117
118
* 58 - 71 Lanthanldes
t 90 - 103 Actinides
140.1
Ce
cerium
58
232.0
Th
thorium
90
140.9 144.2
[145]
150.4
Pr Nd Pm Sm
praseodyinkrnneodymium promethium semarium
69
60
61
62
231.0
Pa
u238.0
pnrtactinilm innium
91
92
(.237]
Np
neptunium
93
[244]
Pu
plutonium
94
152.0
Eu
europium
63
[243]
Am
americium
95
157.3
Gd
gadolinium
64
[247]
Cm
curium
96
158.9
Tb
terbium
65
(.247]
Bk
berkelium
'if1
162.5
Dy
dysprosium
66
164.9
Ho
holmium
ffl
[251] [252)
Cf
Es
cafrfomium ainsteinil.sn
98
99
167.3
Er
erbium
6B
[257]
Fm
fermium
100
168.9
Tm
thulum
69
173.0
Yb
ytterbium
70
(.258]
Md
[259]
No
mendelllloiumnobelium
101
102
175.0
Lu
lutetium
71
[262)
Lr
lawrencium
103
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3 Pages 21-30 |
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Characteristic infrared absorption frequencies for some selected bonds
Bond
C-0
C=C
C=O
C=N
C-H
N-H
0-H
Functional groups
containg the bond
Hydroxy, ester
Aromatic
alkene
compound,
Amide
Carbonyl, carboxyl
ester
nitrile
alkane
Amine
Carboxyl
hydroxy
Characteristic IR
absorption range (in
wavenumbers)/ cm·1
1040-1300
1500-1680
1640-1690
1670-1740
1710-1750
2200-2250
2850-2950
3300-3000
2500-3000
3200-3600
10
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~-r-i··r;;:fniR/__;,,
o- R • [··;'y/,-!._..;'1·,,.,l t:frH<.'J,'(!1':"Cf·f:.1S._;_i:. 'f.,,h,.,
"~ • ,, TECHnoLOGY
\\f.;,:1:;;1,d
•,.:{.{.',;;;if.I
I
2022-m-2Yf{lloI .,
L=
.. x -- :.:..::.2,:,p~~-~-~·~
i
,a=o,d