The electrolysis of other molten substances

2 marks · Hard

Balance the following ionic half-equation for the electrolysis of a molten ionic compound, so that both the number of atoms and the charges are equal on both sides:

where M represents a generic metal.

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

2 electrons

Also accept: 2; 2e-

Common mistakes: Putting 1 electron instead of 2; Placing electrons on the wrong side

Show mark scheme and worked solution

Marking points

M1 · 1 mark · Correctly balances the number of atoms on both sides

A1 · 1 mark · Correctly balances the total charge on both sides (states or shows that 2 electrons must be added)

Worked solution

Each M has a +1 charge, so two M^{+} ions have a total charge of +2. The right side, M_2, is neutral.

To balance charges:

Atoms: 2 M on each side. Charges: +2 + (–2) = 0 left, 0 right. Both atoms and charges are now balanced.