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STUDENT ID:
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UNIVERSITY OF GHANA
(All rights reserved)
BSc./BAHSc./MBChB/DVlVI/B.Ed FIRST SEMESTER EXAMINATIONS: 2020/2021
DEPARTMENT OF CHEMISTRY
CHEM 271: FOUNDATION CHEMISTRY III (2 CREDITS)
INSTRUCTIONS: ANSWER ALL QUESTIONS ON THE QUESTION PAPER
TIME ALLOWED: TWO (2) HOURS
You may End these constants useful:
Molar Gas Constant, R = 8.314 JK"mol", Faraday Constant, F = 96500 J/V.m0l
You may End the following equations useful
_
K,,,K„
J Kb
‘
ri
<1—»·>
_
_
’
Kw
V
K"l.
Define the following as used in acid~basc chemistry and give
an example each with a
suitable equation.
2.
a.
Bronsted—Lowry base:
[2 marks]
b.
Lewis acid:
[2 marks]
c.
Ampholyte:
[2 marks]
Write down proton balance and charge balance for 0.0lM HCN.
A. K. Donkor; L. Hamenu; J.] Harrison.
[2 marks]
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10‘8
3.
What is the pH ofa 5.0 x
4.
A 25 mL of 0.l0M HCN is mixed with 50 mL of 0.05 M aqueous NH;.
1<„[„„,,,] :
10-10
6.2 X
5.
Msolution of Na0H?
and
[3 marks]
1<,,[„„3] = 1.85 X 10-S
a.
Calculate the degree of hydrolysis of the resulting solution.
[2 marks]
b.
What is the pH of the solution?
[2 marks]
a.
State the Henderson-Hasselbalch equation.
A. K. Donkor; L. Hamenu; J.J Harrison.
[l mark]
Page 2 of 5
_
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b.
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Z 5.00 if
What is the coneentration of acetate ion in a buffer solution which has a pH
acetic
Ka
for
acid is
The
is
0.50
M?
(CI·I3COOI-I)
acid
the concentration ofthe acetic
[3 marks]
1.8 x 10'5.
c.
6.
[2 marks]
What is a buffer solution?
A student studying the iron content in a mineral ore was given 3.9 g ofthe ore. The
student dissolved all the ore in sulfuric acid solution to convert all the iron to iron (II)
which was then titrated with 0.15 M potassium permanganate solution. In the titration,
iron (II) was oxidized to iron (III). The titration required 19.5 rnL ofthe permanganate
solution to reach the end point. Use the information provided to answer the questions that
follow.
Z 16.00]
[Fe = 55.85; O
a.
b.
Write down the oxidation and reduction ion—eleetron lizxlllcell rcactions involved in
the titration.
[4 marks]
Deduce the balanced chemical equation for the titration rcaction.
[2 marks]
A. K. Donkor; L. Hamenu; J.} Harrison.
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c.
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What is the percentage of iron in the iron ore sample?
[5 marks]
Ifthe iron was present in the sample as Fe;O3, what would be the percentage by mass
[3 marks]
d.
of Fe;O3 in the sample?
7.
A cell is made up 0fZn/Zn? in a 0.25M [Zng'] solution and Cu/Cu2‘ in 0.015 M [Cu2’]
solution haltlcells at 25°C respectively.
Zn2+(aq) + 2eCu2*(aq) + 2e-
—>
—>
Zn(s)
E° (V) = -0.76 V
Cu(s)
E° (V) = +0.34 V
Write down the balanced haltlreactions at the:
a.
i.
ii.
Anodez
[1 marks]
Cathode:
[1 marks]
A. K. Donkor; L, Hamenu; .1.J Harrison.
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„
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iii.
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Overall cell reactionz
[l marks]
b,
Write the electrochemical cell notation for the cell?
[2 marks]
c.
Calculate the standard emfof the cell (E°mu) at 25°C.
[2 marks]
cl.
Calculate the emfofthe cell (Emu) at 25°C.
[3 marks]
e,
.
Calculate the Gibbs free energy (AG) in kJ/mol ofthe cell at 25°C
[2 marks]
A. K. Donkorg L, Hamenu; J,] Harrison.
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