Question 6
[25]
6.1 Electrolysis of an aqueous solution of copper(II) sulfate, CuSOa, can be carried out
using platinum electrodes.
6.1.1 State an equation for the half-reaction occurring at the positive electrode (anode)
and one observation that could be made as a result.
(2)
6.1.2 State an equation for the half-reaction occurring at the negative electrode
(cathode).
(2)
6.1.3 Describe two changes or observations in the electrolyte as result of these
half-reactions.
(2)
6.1.4 Determine the relative amount, in moles, of products formed at each electrode.
(1)
6.1.5 Identify another compound which will form the same products at the positive and
negative electrodes.
(1)
6.1.6 The same process is carried out using copper electrodes instead of the platinum
electrodes. Describe the changes or observations that take place at both the
electrodes and in the electrolyte.
(3)
6.2 Identify two factors that affect the quantity of copper produced during the
electrolysis of an aqueous copper(II) sulfate solution.
(1)
6.3 Consider the following half cell reactions and their standard electrode potentials:
Ni** (aq) + 2e- Y Ni(s)
£9 =-0.2V
MnOsg (aq) + 8H* (aq) +S5e Y Mn2* (aq) + 4H20 (I) £°=41.51v
6.3.1 State the conditions needed for the electrode potentials to be described as standard.(1)
6.3.2 Deduce a balanced equation for the overall reaction which will occur spontaneously
when the two half cells are connected.
(2)
6.3.3 Identify the reducing agent in the above reaction and determine the change in
oxidation number for the oxidizing agent.
(2)
6.3.4 Determine the cell potential when the two half cells are connected.
(1)
6.3.5 Draw and label a diagram of the voltaic cell from part 6.3. Indicate the anode,
cathode, the direction of the electron movement and ion flow.
(5)
6.3.6 Outline two differences between an electrolytic cell and a voltaic cell.
(2)
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