CHE1010 Tutorial Sheet 5

The University of Zambia
School of Natural Sciences

Chemistry Department
2020 ACADEMIC YEAR TERM 1
CHE1010: Introductory Chemistry for Medical and Health Science
TUTORIAL SHEET 5 May 2021
1. Using given standard reduction potentials, calculate the standard potential of a

copper−zinc cell:
Cu2+(aq) + 2e- → Cu(s) E°= +0.34 V
Zn2+(aq) + 2e- → Zn(s) E° = -0.76 V
2. A silver oxide–zinc cell maintains a fairly constant voltage during discharge (1.60 V).
The button form of this cell is used in watches, hearing aids, and other electronic devices.
The half-reactions are:
Zn(s) + 2OH-(aq) → Zn(OH)2(s) + 2e-
Ag2O(s) + H2O(l) + 2e- → 2Ag(s) + 2OH(aq)
(a) Identify the anode and the cathode reactions.
(b) What’s the overall reaction in this galvanic cell?
3. Write the cell notation for a galvanic cell with the following half-reactions.
(a) Ni(s) → Ni2+(aq) + 2e-
Pb2+(aq) + 2e- → Pb(s)
(b) Galvanic cell constructed from a hydrogen electrode (cathode) in 1.0 M HCl and a
nickel electrode (anode) in 1.0 M NiSO4 solution. The electrodes are connected by a salt
bridge.
4. Write the overall cell reaction and draw the fully labelled for the following galvanic cell:
Fe(s) Fe2+(aq) Ag+(aq) Ag(s)
5. A galvanic cell whose cell reaction is 2Fe3+(aq) + Zn(s) → 2Fe2+(aq) + Zn2+(aq) has a
cell potential of 0.72V. What is the maximum electrical work that can be obtained from
this cell per mole of iron(III) ion?
6. Calculate the maximum work available from 50.0 g of aluminum in the following cell
when the cell potential is 1.15 V.
Al(s) |Al3+(aq) || H+(aq) | O2(g) |Pt.
Note that O2 is reduced to H2O.
7. Using standard reduction electrode potentials, calculate standard free-energy change at

25°C for the following reaction:
3Cu(s) + 2NO3-(aq) + 8H+(aq) → 3Cu2+(aq) + 2NO(g) + 4H2O(l).
8. Copper(I) ion can act as both an oxidizing agent and a reducing agent. Hence, it can react
with itself.
2Cu+(aq) → Cu(s) + Cu2+(aq).
Calculate the equilibrium constant at 25°C for this reaction, using appropriate values of
electrode potentials.
9. What is the maximum electrical work that can be obtained from 6.54 g of zinc metal that
reacts in a Daniel cell, whose cell potential is 1.10 V?
The overall cell reaction is
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
10. Calculate the equilibrium constant (K) for the following reaction from standard electrode
potentials.
Fe(s) + Sn4+(aq) → Fe2+(aq) + Sn2+(aq)
11. Calculate the cell potential of a cell operating with the following reaction at 25°C, in
which [MnO4-] = 0.010 M, [Br-] = 0.010 M, [Mn2+] = 0.15M, and [H+] = 1.0 M.
2MnO4-(aq) + 10Br-(aq) + 16H+(aq) → 2Mn2+(aq) + 5Br2(l) + 8H2O(l)
12. What is the Nickel (II)-ion concentration in the electrochemical cell if the cell potential is
0.34 V at 25°C?
Zn(s) | Zn2+(1.00 M) || Ni2+(aq) | Ni(s)
13. You have 1.0 M solutions of Al(NO3)3 and AgNO3 along with Al and Ag electrodes to
construct a voltaic cell. The salt bridge contains a saturated solution of KCl. Complete the
diagram below by
a) Writing the symbols of the elements and ions in the appropriate areas (both
solutions and electrodes).
b) Identifying the anode and cathode.
c) Indicating the direction of electron flow through the external circuit.
d) Indicating the cell potential (assume standard conditions, with no current flowing).
e) Writing the appropriate half-reaction under each of the containers.
f) Indicating the direction of ion flow in the salt bridge.
g) Identifying the species undergoing oxidation and reduction.
h) Writing the balanced overall reaction for the cell.
14. The zinc–copper electrochemical cell shown below is running under standard conditions.
How would the intensity of light from the bulb change if you were to:
a) Dissolve some additional CuSO4(s) in the CuSO4 solution?
b) Dissolve some additional Zn(NO3)2(s) in the Zn(NO3)2 solution?
c) Add H2O to the CuSO4 solution?
d) Remove the salt bridge?
15. Discuss the advantages and disadvantages of fuel cells over conventional power plants in
producing electricity.
16. Galvanized iron is steel sheet that has been coated with zinc; “tin” cans are made of steel
sheet coated with tin. Discuss the functions of these coatings and the electrochemistry of
the corrosion reactions that occur if an electrolyte contacts the scratched surface of a
galvanized iron sheet or a tin can.
17. Explain why chlorine gas can be prepared by electrolyzing an aqueous solution of NaCl
but fluorine gas cannot be prepared by electrolyzing an aqueous solution of NaF.
18. Chromium plating is applied by electrolysis to objects suspended in a dichromate

solution, according to the following (unbalanced) half-reaction:
How long (in hours) would it take to apply a chromium plating 1.0 x10-2 mm thick to a
car bumper with a surface area of 0.25 m2 in an electrolytic cell carrying a current of 25.0
A? (The density of chromium is 7.19 g/cm3.)
19. In an electrolysis experiment, a student passes the same quantity of electricity through
two electrolytic cells, one containing a silver salt and the other a gold salt. Over a certain
period of time, she finds that 2.64 g of Ag and 1.61 g of Au are deposited at the cathodes.
What is the oxidation state of gold in the gold salt?
20. Due to COVID-19 coupled with erratic power supply from ZESCO, you decide to play
around with galvanic cells and you construct a zinc–copper battery operating at a zero
resistant small light emitting diode (L.E.D) at 25OC as follows:
Zn | Zn2+(0.10 M) || Cu2+ (2.5 M) | Cu
The mass of each solid electrode is 2.00 g.
a) Which of the two is a reducing agent?
b) Calculate the cell potential when this battery is first connected.
c) Calculate the cell potential after 10.0 A of current has flowed for 10.0 hours.
(Assume each half-cell contains 1.00 L of solution.)
d) Calculate the mass of each electrode after 10.0 hours.
e) What will cause the battery to die after some time?

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The University of Zambia

School of Natural Sciences

1. Using given standard reduction potentials, calculate the standard potential of a

7. Using standard reduction electrode potentials, calculate standard free-energy change at

2MnO4-(aq) + 10Br-(aq) + 16H+(aq) → 2Mn2+(aq) + 5Br2(l) + 8H2O(l)

18. Chromium plating is applied by electrolysis to objects suspended in a dichromate

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