Chapter 26
Question 14 (02Chem2)
A VCE chemistry student sets up a galvanic cell using two standard half cells with half reactions.
half cell 1:
Cr3+(aq) + e–  Cr2+(aq)
half cell 2:
Cr(s)  Cr2+(aq) + 2e–
Suitable materials for the electrodes of the two half cells are
Half cell 1
Half cell 2
Platinum
Platinum
A.
Platinum
Chromium
B.
Chromium
Chromium
C.
Chromium
Platinum
D.
Question 15 (02 Chem2)
A student decided to silver-plate a locker key using the apparatus shown.
In this cell, the key is the
A.
B.
C.
D.
anode and is connected to the positive terminal of the power supply.
anode and is connected to the negative terminal of the power supply.
cathode and is connected to the positive terminal of the power supply.
cathode and is connected to the negative terminal of the power supply.
Question 19 (02 Chem2)
Hydrogen peroxide can act as a reductant according to the half equation
O2(g) + 2H+(aq) + 2e–  H2O2(aq);
Eo = +0.68 V
Which of the following could all be reduced by hydrogen peroxide?
A.
Fe2+(aq), Cu(s), I–(aq)
B.
Ag+(aq), Br2(aq), H2O2(aq)
C.
Ag(s), Br–(aq), Fe2+(aq)
D.
I2(s), Cu2+(aq), Fe3+(aq)
Use the experimental arrangement below to answer Question 9.
The experimental arrangement shows a
• silver rod dipping into a 1.0 M solution of AgNO3(aq)
• nickel rod dipping into a 1.0 M solution of Ni(NO3)2(aq)
The solutions are connected to each other with a salt bridge consisting of an inverted U-tube
containing ammonium nitrate solution.
Question 9 (03 Chem2)
Which of the following alternatives correctly describes the polarity of, and the reaction that occurs at,
the anode of this cell?
anode polarity
reaction at the anode
negative
Ag+(aq) + e– → Ag(s)
A.
negative
Ni(s) → Ni2+(aq) + 2e–
B.
positive
Ag+(aq) + e– → Ag(s)
C.
positive
Ni(s) → Ni2+(aq) + 2e–
D.
Question 8 (03 Chem2)
d. Part of the electrochemical series is given below and should be used to answer the following
questions.
i. Select two of the above half reactions which together indicate that, in aqueous solution, NH3 bonds
to Co3+ rather than to Co2+.
1 mark
ii. Explain, using the above data, why aqueous solutions containing Co(H2O)63+(aq) might be too
unstable to be conveniently used in the laboratory.
1 mark
Question 7 (04 Chem2)
A student is planning to set up a demonstration of a galvanic cell using half cells constructed as
follows.
• Half cell 1: a calcium electrode in a beaker containing an aqueous solution of Ca2+ ions
• Half cell 2: a platinum electrode in a beaker containing an aqueous solution of a mixture of Sn4+
and Sn2+ ions
A salt bridge would connect the two beakers. The electrodes would be attached to a voltmeter.
This particular cell is impractical because
A. solid calcium (Ca) will react directly to reduce water to hydrogen gas.
B. there is no solid tin (Sn) in the half cell containing Sn4+(aq) and Sn2+(aq).
C. there are no known ionic compounds of calcium that are soluble in water.
D. Sn4+(aq) will be in contact with Ca and will oxidise it to Ca2+(aq).
Question 8 (04 Chem2)
In which one of the following sets of substances are all members of the set able to undergo a
spontaneous redox reaction with pure water?
A. Fe, Co2+, Cl2
B. F2, Mg, Au+
C. H+, Na+, Br2
D. Li, F2, Ag+
Question 5 (04 Chem2)
A student carries out the electrolysis of a 1.0 M solution of sodium chloride using graphite electrodes.
The set-up for this experiment is shown below.
a. Write an equation for the half
reaction that occurs at the cathode.
1 mark
b. Two different gases are produced at
the anode. Write equations for the two half reactions that result in the formation of these two gases.
i. Equation for half reaction that produces gas 1
1 mark
ii. Equation for half reaction that produces gas 2
1 mark
c. Using the same current and electrodes, the student carries out a second electrolysis, this time of a
saturated solution (approximately 6 M) of sodium chloride instead of a 1.0 M solution. What
difference, if any, would you expect in the product or products formed at the
i. cathode?
1 mark
ii. anode?
1 mark
Total 5 marks
Question 6 (05 Chem2)
Which one of the following would be predicted to spontaneously oxidise aqueous iodide ions but not
aqueous
chloride ions?
A. Au+(aq)
B. Sn2+(aq)
C. Fe2+(aq)
D. Br2(aq)
Question 8 (05 Chem2)
A galvanic cell consists of one half cell that is made up of an inert graphite electrode in a solution
containing
1.0 M Fe2+(aq) and 1.0 M Fe3+(aq) at 25°C.
Which one of the following could be used as the second half cell so that the polarity of the electrode
in this
second half cell is positive?
A. a lead electrode in a solution of 1.0 M Pb2+(aq)
B. a silver electrode in a solution of 1.0 M Ag+(aq)
C. an iron electrode in a solution of 1.0 M Fe2+(aq)
D. an inert graphite electrode in a solution of 1.0 M Br.(aq)
Question 6 (05 Chem2)
Give concise explanations for each of the following.
b. Hydrogen gas is bubbled through a solution of 1.0 M Fe3+(aq) ions. On the basis of the
electrochemical
series, a redox reaction is predicted to occur. In practice, no reaction occurs at room temperature.
1 mark
constructed from the following half cells, at 25°C.
electrode half cell solution (all concentrations 1.0 M)
half cell 1 silver colourless solution of AgNO3
half cell 2 copper blue-coloured solution of CuCl2
The half cells are connected with a salt bridge and the electrodes are joined by a wire.
Question 4 (06 Chem2)
Which one of the following is likely to occur?
A. The copper electrode will increase in mass.
B. Bubbles of gas will form at the copper electrode.
C. The concentration of silver ions in solution will increase.
D. The blue colour of the copper (II) chloride solution will become more intense.
Question 5 (06 Chem2)
When the current is ß owing
A. the anode is positive and the cathode is negative.
B. an oxidation reaction occurs at the positive electrode.
C. anions in the salt bridge move towards the negative electrode.
D. electrons travel in the external circuit from the cathode to the anode.
Question 11 (07 Chem2)
Consider the following half cells which are set up under standard conditions.
half cell electrode electrolyte
I metal A A2+(aq)
II platinum B2+(aq) and B3+(aq)
III metal C C+(aq)
. When a galvanic cell is constructed from half cell I and half cell II, the electrode in half cell II is
negative.
. When a galvanic cell is constructed from half cell II and half cell III, the electrode in half cell III is
negative.
The strongest oxidant is
A. A2+(aq)
B. B2+(aq)
C. B3+(aq)
D. C+(aq)
Question 7 (07 Chem2)
The following diagram represents a H+(aq)/H2(g) half cell for the reaction
2H+(aq) + 2e. ! H2(g)
a. i. For this half cell, identify an appropriate material for electrode Z.
ii. For this half cell to be a standard half cell, state
. the temperature at which it must operate ____________
. the required pH of the solution of H+(aq) ions ______________________
1 + 2 = 3 marks
b. A galvanic cell consists of the following half cells which have been set up under standard
conditions.
. Half cell 1: the H+(aq)/H2(g) half cell described in part a.
. Half cell 2: a cadmium (Cd) electrode in a solution containing Cd2+(aq)
After some time, the pH in half cell 1 has increased. Use this information to identify the species in this
galvanic cell which is the stronger reductant and explain how you reached this conclusion.
The stronger reductant is
Explanation
2 marks
c. A second galvanic cell consists of the following half cells.
. Half cell 1: an inert electrode in 100.0 mL solution of 1.00 M X2+(aq)
. Half cell 2: an electrode of Cu(s) in 100.0 mL solution of 1.00 M Cu2+(aq)
This galvanic cell is shown in the diagram below.
After discharging 2654 C of
electricity, the concentration of the X2+(aq) in solution in half cell 1 was found
to be 0.725 M. The volume of the solutions in the two half cells had not changed.
i. Calculate the amount, in mol, of X2+(aq) that reacted in half cell 1.
ii. Calculate the ratio of n(X2+) reacted to n(e.) that passed through the cell.
That is, calculate: n(X2+) reacted: n(e.)
iii. State the oxidation state of the product of the half reaction in half cell 1.
iv. Write an equation for the half reaction that occurred at the electrode of half cell 1.
2 + 2 + 1 + 1 = 6 marks
Total 11 marks
Question 8 (07 Chem2)
Faraday.s constant is deÞ ned as the charge on one mole of electrons. The value of Faraday.s constant
can be
determined experimentally by electrolysis using inert electrodes.
A current of 1.62 A is passed through a solution of copper (II) nitrate for 581 s. At the end of that
time, the
copper deposited at the negative electrode was collected. Its mass was found to be 0.306 g.
a. Write an equation for the half reaction occurring at the negative electrode of this electrolytic cell.
1 mark
b. Use the experimental data given above to calculate, to an appropriate number of signiÞ cant Þ
gures,
the
. charge, in coulombs, that was passed through the electrolytic cell
. amount, in mol, of copper deposited at the negative electrode.
3 marks
c. Use the values obtained in part b. to calculate the experimentally determined value of Faraday.s
constant.
2 marks
d. The value of Faraday.s constant given in your data sheet is 96 500 C mol.1. The experiment above
was
repeated and a value for Faraday.s constant was found to be 98 400 C mol.1. The amount of charge
passed
is accurately known. Describe one possible source of experimental error which would result in
obtaining
an experimental value that was higher than the one given in the data sheet.
1 mark
Total 7 marks