Some of the demonstrations could be duplicated in a school laboratory and used in conjunction with the programme, which employs graphics to highlight what is being illustrated.

The programme is divided into three sequences:

• 1.Electrolysis of a Melt
• 2.Electrolysis of a Solution
• 3.Electroplating

The programme could be used at any stage of the teaching of electrolysis and electroplating, and would make an excellent summary or revision aid. It could be shown in full or in discrete sections as appropriate.

Electrolysis of a Melt

00.00 The usefulness of electrolysis

Aluminium is manufactured by using electricity to decompose aluminium oxide.

00.56 Electrolysis of molten lead bromide

Molten lead bromide is electrolysed using simple laboratory apparatus. This produces lead at the negative electrode and bromine at the positive electrode.

02.57 Explaining the electrolysis of molten lead bromide

Lead bromide contains positive lead ions and negative bromine ions. During electrolysis, the positive ions move to the negative electrode and the negative ions move to the positive electrode. The discharge of these ions at the electrodes is illustrated by an animated graphic sequence.

04.00 Electrolysis of zinc chloride

The behaviour of molten zinc chloride during electrolysis is investigated.

04.59 Industrial electrolysis

On a much bigger scale, a similar method is used to extract a reactive metal, such as aluminium, from its ore.

Electrolysis of a Solution

05.22 Electrolysing sodium chloride solution

The electrolysis of an aqueous solution of salt produces useful substances. This is demonstrated in the laboratory using carbon electrodes. The gas which collects at the anode bleaches litmus paper, which shows that the gas is chlorine. The gas at the cathode burns with a squeaky pop: it is hydrogen.

07.46 Explaining the electrolysis of sodium chloride solution

The electrolyte contains sodium and chloride ions from salt. Hydrogen and hydroxide ions come from water. Both sodium and hydrogen ions - which are positive - go to the negative electrode, but only the hydrogen ions are discharged. At the positive electrode, only the chloride ions lose their charge.

08.46 Using the products of sodium chloride electrolysis

Examples are given of how we use chlorine, hydrogen and sodium hydroxide.

Electroplating

09.21 Electrolysing copper sulphate solution with carbon electrodes

Copper sulphate solution produces oxygen gas at the positive electrode and copper metal at the negative electrode when it electrolysed using carbon electrodes.

10.46 Electrolysing copper sulphate solution with copper electrodes

If copper electrodes are used, copper is again produced at the negative electrode but no oxygen is produced at the positive electrode. Mass measurements before and after electrolysis show a gain at the negative electrode and a loss at the positive electrode. This suggests that copper ions are discharged at the negative electrode but are going into solution at the other electrode.

13.07 Electroplating copper

A circuit with a reactive copper anode can be used to plate objects with copper. The object to be plated is made the negative electrode; the positive electrode is copper; and the electrolyte contains copper sulphate. The thickness of the copper deposit depends on the current flowing in the circuit.