Predicting Products of Electrolysis

Question 1

Can an ionic solid be electrolysed?

Answer 1

No

Question 2

Why can’t an ionic solid be electrolysed?

Answer 2

Because the ions are in fixed positions and can’t move.

Question 3

Can molten ionic compounds be electrolysed?

Answer 3

Yes

Question 4

Why can molten ionic compounds be electrolysed?

Answer 4

Because the ions can move freely and conduct electricity.

Question 5

What happens to positive metal ions at the cathode?

Answer 5

They are reduced to metal atoms.

Question 6

What happens to negative ions at the anode?

Answer 6

They are oxidised to atoms or molecules.

Question 7

What is the example of OIL RIG at the electrodes for PbBr2?

Answer 7

At the anode, you would see a brown vapour of bromine gas.
2Br- → Br2 + 2e-

At the cathode, you would see a silver coloured liquid as molten lead is formed.
Pb 2+ + 2e- → Pb

Question 8

In aqueous solutions, as well as the ions from the ionic compound, what other ions are present?

Answer 8

There will also be hydrogen ions (H+) and hydroxide ions (OH-) from the water:
H2O (l) ⇌ H+ (aq) + OH- (aq)

Question 9

At the cathode, hydrogen gas can be produced if what are present?

Answer 9

H+ ions and metal ions need to be present, and the metal must be more reactive than hydrogen (e.g. sodium).

Question 10

At the cathode, what happens if the metal is less reactive than hydrogen?

Answer 10

If the metal is less reactive than hydrogen (e.g. copper or silver), then a solid layer of the pure metal will be produced instead.

Question 11

At the anode, if OH- and halide ions (Cl-, Br-, I-) are present, what is produced?

Answer 11

Molecules of chlorine, bromine or iodine will be formed.

Question 12

At the anode, if no halide ions are present, what is produced?

Answer 12

Oxygen will be formed.