4.3 CHAPTER 4. ELECTROCHEMICAL REACTIONS
- At the positive anode,copper metal is oxidisedto form Cu2+ions. This is
why it appears that some of the copper has dissolved from the electrode.
The half-reaction that takes place is as follows:
Cu(s)→ Cu2+(aq) + 2e−(oxidation half reaction) - The amount of copperthat is deposited at one electrode is approximately
the same as the amount of copper that is dissolved from the other. The
number of Cu2+ions in the solution therefore remains almost the same
and the blue colour of the solution is unchanged.
Conclusion:In this demonstration, an electric current was used to split CuSO 4 into its
component ions, Cu2+and SO^24 −. This process is called electrolysis.The electrolysis of water ESCBP
Water can also undergoelectrolysis to form hydrogen gas and oxygen gas according to
the following reaction:
2H 2 O(l)→ 2H 2 (g) + O 2 (g)This reaction is very important because hydrogengas has the potential to be used as an
energy source. The electrolytic cell for this reaction consists of two electrodes (normally
platinum metal), submerged in an electrolyte and connected to a sourceof electric cur-
rent.
The reduction half-reaction that takes place at the cathode is as follows:
2H 2 O(l) + 2e−→ H 2 (g) + 2OH−(aq)The oxidation half-reaction that takes place at the anode is as follows:
2H 2 O(l)→ O 2 (g) + 4H+(aq) + 4e−A comparison of galvanic and elec-
trolytic cells
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It should be much clearer now that there are a number of differences between a galvanic
and an electrolytic cell. Some of these differences have been summarised in table 4.1.