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ICH402S - INTRODUCTION TO CHEMISTRY B - 1ST OPP - NOV 2022 |
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nAm I BIA un IVERSITY
OF SCIEnCE Ano TECHn OLOGY
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: INTRODUCTIONTO CHEMISTRYB
SESSION:
NOVEMBER 2022
PAPER:
N/A
DURATION: 3 HOURS
MARKS:
100
EXAMINER(S)
MODERATOR:
FIRST OPPORTUNITY EXAMINATION PAPER
Ms Elvira van Wyk
Mr Victor Nwagbara
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 12
THIS EXAMINATION PAPER CONSISTS OF 12 PAGES (Excluding this front page)
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Question 1
[15]
Dinitrogen pentoxide, N2Os,is dissolved in an inert solvent (solv) and the rate of
Decomposition of N2Osis investigated. This reaction produces nitrogen dioxide, which
remains in solution, and oxygen gas.
1.1
Suggest what measurements could be used to follow the rate of this reaction
from the given information.
(1)
1.2
In a separate experiment, the rate of the decomposition of N2Os(g)is investigated.
The graph below shows the results obtained:
0.30
0.25
0.20
0.15
0.10
0.05
0
I
'-~
•-~ ~ct-
I
,->- >-+- I\\ II.
I->- >-- >-I- ~I' i'\\~
1'-1,
,r, ....
I
-+ I->-
,i'.. .....
I
r--
.....
-
r-
I
-- -f'7 I
0 100 200 300 400 500 600 700
time/s
The reaction is first order with respect to N2Os. This can be confirmed from the
graph using half-lives.
1.2.1 Explain the term half-life of a reaction.
(1)
1.2.2 Determine the half-life of this reaction.
(1)
1.2.3 Suggest the effect on the half-life of this reaction if the initial concentration of
N2OsIs halved.
(1)
1.2.4 Use the graph in 1.2 to determine the rate of reaction at 200 s. Show your
working and the unit.
(2)
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The rate equation for this reaction is shown:
1.2.5 Use your answer to 1.2.4 to calculate the value of the rate constant, k, for this
reaction and state its units.
(1)
1.3
Nitrogen dioxide reacts with ozone, 03, as shown:
The rate equation for this reaction is rate= k [N02][03].
Suggest a possible two-step mechanism for this reaction.
(2)
1.4
GasesA and B react as shown in the following equation:
2A{g) + B(g) C(g) + D(g)
The initial rate of the reaction was measured in a series of experiments at a
constant temperature. The following rate equation was determined:
rate= k[A]2
An incomplete table of data for the reaction between A and Bis shown in the
Table below.
Experiment
1
Initial [A] / mol dm- 3 Initial [B] / mol dm-3 Initial rate/ mol dm- 3 s-
-
4.2 X 10- 3
2.8 X 10- 3
3.3 x 10- 5
2
7.9 X 10- 3
2.8 X 10- 3
3
5.6 X 10- 3
1.8 X 10- 4
1.4.1 Use the data from Experiment 1 to calculate a value for the rate constant, k, at
this temperature. What is the units of k?
(3)
1.4.2
Use your value of k from Question 1.4.1 to complete the Table for the reaction
between A and B.
{If you have been unable to calculate an answer for Question 1 (a), you may
assume a value of 2.3 This is not the correct answer.)
{2)
1.4.3 The reaction is zero order with respect to B. State the significance of this zero
order for the mechanism of the reaction.
(1)
2
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Question 2
[15]
When dilute sulfuric acid is electrolysed, water is split into hydrogen and oxygen.
A current of x A is passed through the solution for 14.0 minutes. 462 cm3 of hydrogen
are produced at the cathode, measured under room conditions.
2.1
Calculate the number of hydrogen molecules produced during the electrolysis. (2)
2.2
Calculate the total number of electrons transferred to produce this number of
hydrogen molecules.
(1)
2.3
Calculate the quantity of charge, in coulombs, of the total number of electrons
calculated in 2.2.
(1)
2.4
Calculate the current, x, passed during this experiment.
(1)
2.5
The standard entropies, ~5°, of three species are given in the table.
species
H2O(I)
H2(g)
O2(g)
5°/JK- 1 mol- 1
+70
+131
+205
2.5.1 Calculate ti5° for the reaction 2H2O(I) 2H2(g)+ O2(g).
(1)
2.5.2 tiH 9 for the reaction 2H2O(I) 2H2(g)+ O2(g)is +572 kJmo1-1.
Calculate tiG 0 for this reaction at 298 K.
(2)
2.5.3
Predict the effect of increasing temperature on the spontaneity of this reaction.
Explain your answer.
(1)
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2.6 The diagram shows an incomplete voltaic cell with a light bulb in the circuit.
Mg{s)
Ag{s)
MgS04 (aq)
AgN03 (aq)
2.6.1 Identify the missing component of the cell and its function.
(2)
2.6.2 Deduce the half-equations for the reaction at each electrode when current
flows.
(2)
2.6.3 Redraw the diagram with the location and direction of electron movement when
current flows.
(1)
2.6.4
__ --- Calculate the cell potential, in V, using the given data below:
Qlllllllad-..-.._
a.i.lal..-
r'(V)
IJ'("'ll •••
U(•J
-l.O.
°' "(aq) + .-
cu•~
Hu.;
1:·("'IJ + .-
K<•)
-2,93
.- so;·c,<+0•H"<,q_)..
H,SO,t"I) >110(1}
~'1.17
.. (".,'·c•'!:l:c-
N,"("'I)
C>t•J
N>{I)
-t.WJ
-l.71
0: ·c"-l) + z,-
-1/>Jt..t_}H,O{IJ ,- Zc-
Cu(')
ZOW(~)
~(l:i.i
..o.w
Mg'•(•i\\).;1.-
1'-e(sJ
-~.1,
= 0.,4(.:sq)... c-
Cu{<)
-o.sz
Al'"('"!)+]•·
Al(s)
-1.(,6
;,,bl+~-
l"(,q,l
..;.o.s-,
Mot•(~ql-. ::z~w
H,Ot1)+•·
zv•(•'ll -.:.-
I'< .,,~1+:.-
>In(<)
-jll,(D4 OH"(,q}
ln(•J
f<(S)
-1.18
-0.1.13
-o.,~
-OA1!i
P<'"C>11Hc
... ..-.(.~ -
- 111,.(l)+c:-
-;0,<t)+?H.(:q)-.. le-·
w•(oql
,\\£1,>)
~r•(aj
H O(lJ
+Qn
*<180
-tO'l
! ;:3
Nt:•(;aq) -f
SI(<.:)
-o.:r,
t:r,(Y,'(,q)., HH'("t) + <,,:·
Cr'"("'l) i· 7H,O(IJ
... 1.:tt.
s (.>:t)... ?~·
SA{s)
-u.u
' ,<al•.-
Cl"("()
• l 36
(1)
pt,'·t.q) + 2<"
H"1oqt+ •·
p •)
-iH,w
-0.ll
o.uo
Mnu; q) +BH'("'l) • 5•·
1¥t<1),-:+:-
Mn'•+ (H.Oll)
F"(>q)
•1.s1
'1'U'7
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2 Pages 11-20 |
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Question 3
[18]
3.1
Calcium hydroxide is slightly soluble in water.
3.1.1. Write an equation to show the dissociation of calcium hydroxide, Ca(OH)i(s), in
aqueous solution. Include state symbols.
(1)
3.1.2 Calculate the solubility, in mol dm- 3, of Ca(OH)i.
[Ksp:Ca(OH)i, 5.02 x 10-6 moI3 dm- 9]
(2)
3.1.3 Suggest how the solubility of Ca(OH)i in aqueous NaOH compares to its solubility
in water. Explain your reasoning.
(1)
3.2
Silver sulfate, Ag2SO4,is sparingly soluble in water. The concentration of its
saturated solution is 2.5 x 10-2 mol dm- 3 at 298 K.
3.2.1 Write an expression for the solubility product, Ksp,of Ag2SO4,and state its units.(1)
3.2.2 Calculate the value for Ksp(Ag2SO4a)t 298 K.
(1)
3.2.3 Using Ag2SO4as an example, redraw and complete the following Hess' Law
energy cycle relating the:
(5)
• lattice energy, !::;.Hz°at,t
• enthalpy change of solution, t::;.H01; , and
• enthalpy change of hydration, t::;.H'hyd
On your diagram:
• include the relevant species in the two empty boxes,
• label each enthalpy change with its appropriate symbol,
• complete the remaining two arrows showing the correct direction of
enthalpy change.
5
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3.3
Another electrochemical cell is set up as follows:
Pt I Fe3+, Fe2+11 Ag+I Ag
Ag2SO4(s)is formed at the Ag electrode
3.3.1 Use the Data in 2.6.4 to calculate the value of under standard conditions, stating
which electrode is the positive one.
(1)
3.3.2 How would the actual Ecelol f the above cell compare to the under standard
conditions? Explain your answer.
(1)
3.3.3 How would the Ecelol f the above cell change, if at all, if a few cm3 of
concentrated Na2SO4(aq)were added to:
• the beaker containing Fe3+(aq) + Fe2+(aq),
• the beaker containing Ag2SO4(aq)?
(2)
3.3.4 Explain any changes in Ecelyl ou have stated in 3.3.3.
(1)
3.3.5 Solutions of iron(III) sulfate are acidic due to the following equilibrium.
[Fe(H2O)5]3+(aq)[Fe(H2O)s(OH)]2+(aq+) W(aq) Ka= 8.9 x 10-4mol dm- 3
Calculate the pH of a 0.1 mol dm- 3 solution of iron(III) sulfate, Fe2(SO4)3.
(2)
Question 4
[10]
4.1
Solution Y is hydrochloric acid, HCI (aq). Solution Z is aqueous 4-chlorobutanoic
acid, Cl(CH2hCO2H(aq).The pKaof Cl(CH2hCO2H(aq)is 4.52. The pH of both
solutions is 4.00.
4.1.1 Write an expression for the Kaof Cl (CH2hCO2H(aq).0
(1)
4.1.2 Write a mathematical expression to describe the relationship between Ka
and pKa.
(1)
4.1.3 Calculate [W] in solutions Y and Z.
(1)
4.1.4 Calculate the ratio:
[HCI ] dissolved in solution Y
[Cl(CH2hCO2H]dissolved in solution Z
(2)
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4.2
A buffer solution of pH 5.00 is produced by adding sodium propanoate to 5.00 g
of propanoic acid in 100 cm3 of distilled water. Calculate the mass of sodium
propanoate that must be used to produce this buffer solution.
The Ka of propanoic acid is 1.35 x 10-s mol dm- 3.
(3)
[Mr: propanoic acid, 74.0; sodium propanoate, 96.0]
4.3 Some dilute sulfuric acid is mixed with a small sample of the buffer solution
described in 4.2. The final pH of the mixture is close to 1.
Explain this observation.
(2)
Question 5
[12]
Propene, C3H&,reacts with H2Oin the presence of an acid catalyst to form an alcohol with
Molecular formula C3HsO.
5.1
Name this type of reaction.
(1)
5.2
Name the catalyst used and state the conditions needed for this reaction to
occur.
(2)
5.3
Redraw and Complete the table to show the numbers of sigma (a) bonds and
pi (rr) bonds present in propene, C3H&a, nd C3HsO.
(2)
a
IT
C3H6
C3HgO
5.4
5.4.1
5.4.2
The reaction of propene, C3H&w, ith H2Ooccurs in a two-step mechanism.
In step 1 C3H&reacts with the catalyst, W, to form a carbocation.
Draw structures to identify the more stable and less stable carbocations which
can form in step 1. Explain your answer.
(3)
Name the major organic product formed from the reaction of propene, C3H&w, ith
H2O.
(1)
5.5
2-bromopropane reacts to form propene, hydrogen bromide and water under
certain conditions.
5.5.1 Name this type of reaction.
(1)
5.5.2 Describe the reagents and conditions needed to favour this reaction.
(2)
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Question 6
[9]
The structure of phenylethanoic acid is shown:
OH
6.1
Phenylethanoic acid can be synthesised using benzene as the starting material.
In the first stage of this synthesis, benzene reacts with chloromethane in the
presence of an A/C/3catalyst to form methylbenzene. Chloromethane reacts with
A/C/3to form two ions. One of these is the carbocation +cH3.
6.1.1 Write an equation for the reaction between chloromethane and A/C/3.
(1)
6.1.2
Redraw the diagrams below and draw the mechanism of the reaction between
benzene and +cH3. Include all relevant curly arrows, charges and the structure
of the intermediate.
{3)
0
intermediate
6.2
A three-step synthesis of phenylethanoic acid from methylbenzene is shown:
_.... step3
compound Q
6.2.1 State reagents and conditions for step 1.
(1)
6.2.2 Suggest the structure of compound Q.
(1)
6.2.3 State reagents and conditions for steps 2 and 3.
(2)
6.2.4 Draw the structure of an organic by-product that forms in step 1.
(1)
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Question 7
[10]
7.1 The reason for the wide variety of organic compounds is isomerism, either
structural isomerism or stereoisomerism.
7.1.1 Explain the meaning of the term structural isomerism.
(2)
7.1.2 Explain the meaning of the term stereoisomerism.
(2)
7.2
Pent-1-ene, CH2=CH(CH2)2CHd3o, es not show stereoisomerism.
7.2.1 Give two reasons why pent-1-ene does not show stereoisomerism.
(2)
7.2.2 A structural isomer of pent-1-ene is used as the monomer to form a polymer.
The repeat unit of this polymer is shown:
tHc1-c CI H:)-
! L,CH3
Draw the displayed formula of the monomer used to make this polymer. Give
the name of the monomer
(2)
7.2.3
A different structural isomer of pent-1-ene shows geometrical isomerism. Draw
the structure of one of the two geometrical isomers with the formula CsH10.
Give the full name of this isomer.
(2)
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3 Pages 21-30 |
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Question 8
[6]
Titration curves, labelled E, F, G and H, for combinations of different aqueous solutions
of acids and bases are shown in the diagrams below. All solutions have concentrations
of 0.1 mol dm- 3•
E
14--.----------~
12
10
pH 8
6
4
2
o+-~-~~-~--i
0 10 20 30 40 50
Volume/cm 3
F
14--.-----------,
12
10
pH 8
6
4
2
0 10 20 30 40 50
Volume/cm 3
G
14--.----------~
12
10
8
pH 6
4
2o-------_,
0 10 20 30 40 50
Volume/cm 3
H
14~------~
12
10
pH 8
6
4
2o--~~--~-
o 10 20 30 40 50
Volume/cm 3
8.1
From the curves E, F, G and H, choose the curve produced by the addition of:
8.1.1 · sodium hydroxide to 25 cm3 of ethanoic acid
(1)
8.1.2 ammonia to 25 cm3 hydrobromic acid (HBr)
(1)
8.1.3 hydrochloric acid to 25 cm3 of potassium hydroxide
(1)
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8.2
The table below shows information about some acid-base indicators.
Indicator
pentamethoxy red
naphthyl red
4-nitrophenol
cresol purple
pH range
1.2-3.2
3.7-5.0
5.6-7.0
7.6-9.2
Lower pH colour
violet
red
colourless
yellow
Higher pH colour
colourless
yellow
yellow
purple
8.2.1 Which indicator in the Table could be used for the titration that produces curve E
but not for the titration that produces curve F?
(1)
8.2.2 Give the colour change at the end point of the titration that produces curve H
when naphthyl red is used as the indicator.
(1)
8.2.3 A beaker contains 25 cm3 of a buffer solution at pH = 6.0
Two drops of each of the four indicators in Table 2 are added to this solution.
State the colour of the mixture of indicators in this buffer solution.
You should assume that the indicators do not react with each other.
(1)
Question 9
[4]
9.1
Write the equations for the following decay processes:
Positron emission from silicon-26
(2)
9.2 The radioisotope fluorine-21 had an initial mass of 80 milligrams. 20 milligrams
of sample remained unchanged after 8.32 s. What is the half life of F-21?
(2)
THE END
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The Periodic Table of the Elements
1
2
3
4
5
6
7
0
1.0
H
(1)
(2)
Key
hydrogen
1
(13) (14) (15) (16) (1n
6.9
Li
lithium
3
9.0
Be
beryllum
4
relative atomic mass
symbol
name
atomic (proton) number
10.8
B
boron
5
12.0
C
carbon
6
14.0
N
ritrogen
7
16.0
0
oxygen
8
19.0
F
fluorine
9
23.0
24.3
Na Mg
27.0
Al
28.1
SI
31p.0
32s.1
35.5
Cl
&Odium m&gneGlum
11
12
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
o.luminlum silicon pho8ph0r1111 suHur
1!1
14
15
18
chbrine
17
39.1
40.1
45.0
47.9
50.9
52.0
54.9
55.8
K
Ca
Sc
1i
V
Cr Mn Fe
potasslllTI calcium scandium titanllnl vmmcfium chrvrnlum ITl8ngllllelle
Iran
19
20
21
22
23
24
25
26
58.9
Co
cobalt
71
58.7
Ni
nickel
28
63.5
Cu
copper
29
65.4
Zn
zl11c
30
88.7
Ga
gallium
31
72.6
74.9
Ge As
germanium arsenic
32
33
79.0
Se
selenium
34
79.9
Br
bromine
35
85.5
Rb
rubidium
37
87.6
Sr
strontium
38
88.9
V
yttrium
39
91.2
'Zr
zirconium
40
92.9
Nb
niobium
41
96.0
1.97] 101.1
Mo
Tc
Ru
molybdem.mtechmltium rutt,-,lum
42
43
44
102.9
Rh
rhodium
45
106.4
Pd
palladium
48
107;9
Ag
silver
47
112.4
Cd
cadmium
48
114.8
In
ndiurn
49
118.7
Sn
tin
50
121.8
Sb
antimony
51
127.6
Te
tellurium
52
126.9
I
Iodine
53
132.9
Cs
caesium
55
137.3
Ba
barium
56
1L38a..9
178.5
Hf
lanthanum hafnlllTI
57
72
180.9
Ta
tuitalum
73
w 183.8
tungsten
74
186.2
Re
rhenium
75
190.2
Os
osmium
76
192.2
Ir
Iridium
n
195.1
Pt
plallnum
78
197.0
Au
gold
79
200.6
Hg
mercury
BO
n204.4
thallium
81
207.2
Pb
lead
82
209.0
Bi
bismuth
83
[209]
Po
polonium
84
[210)
At
astatine
BS
[223]
Fr
francium
87
[226)
Ra
radium
88
actinium
89
[267)
Rf
[270)
Db
[269]
Sg
[270]
Bh
nd!te!fonlium dubt1ium 881lborgi1Al1 bohrium
104
105
106
107
(.'270)
Hs
hassium
108
[278]
[281)
[281]
[285]
Mt
Os
Rg
Cn
meitnerium dennatadtiurrnoentgenium copenidum
109
110
111
112
[286]
Nh
nhonlum
113
[289)
[289]
[293]
(294)
Fl
Mc
Lv
Ts
flerovitJm mOIICXMUlJiTvIermorantennneeeine
114
115
116
117
I
4.0
He
helium
2
20.2
Ne
neon
10
39.9
Ar
argon
18
83.8
Kr
krypton
36
131.3
Xe
xenon
54
[222)
Rn
radon
86
[294]
0g
118
* 58 - 71 Lanthanides
t 90-103 Actinides
14-0.1
Ce
cerium
58
232.0
Th
thorium
90
140.9
Pr
144.2
Nd
[145) 150.4
Pm Sm
insec>drmnietmodymium promethium samarium
59
60
61
62
231.0
Pa
protactinium
91
23u8.0
U"anium
92
[237]
Np
neptunium
93
[244]
Pu
plutonium
94
152.0
Eu
157.3
Gd
europium gadolinium
63
64
(243)
Am
americium
96
[247]
Cm
curium
96
158:9
Tb
terbium
65
[247]
Bk
berkelium
97
162.5
Dy
dysprosium
66
1H64.o9
holmium
67
(251]
Cf
californium
98
(252]
Es
einsteinium
99
167.3
Er
eri>ium
68
[257]
Fm
fennium
100
168.9
Tm
thulium
69
173.0
Yb
yttedlium
70
175.0
Lu
lutetium
71
(258] (259] [262]
Md No
Lr
menclelevium nobelium lawnncium
101
102
103
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