Electrolysis of salts

When a molten salt is electrolysed ions are discharged as atoms or molecules at the electrodes.

• Molten lead bromide
• Anode product is bromine gas
• Cathode product is molten lead metal

Reaction at Cathode

Pb 2+ + 2e- ----> Pb 

Reaction at Anode

2Br- ----> Br2 + 2e-

When a molten salt is electrolysed ions are discharged as atoms or molecules at the electrodes.

• Molten lead bromide
• Anode product is bromine gas
• Cathode product is molten lead metal

Reaction at Cathode

Pb 2+ + 2e- ----> Pb 

Reaction at Anode

2Br- ----> Br2 + 2e-

Water ionises to a very small extent, so in an aqueous solution of a salt there are hydrogen ions and hydroxide ions as well as ions of the dissolved salt. 

• Cu 2+ and Cl - from the salt
• H+ and OH- from the water

Copper loses it's charge more readily than hydrogen ions

Chloride loses it's charge more readily then hydroxide ions

Therefore:

• Copper metal is discharged from the cathode
• Chlorine gas is discharged from the anode
• Leaving water

• Cu2+ and SO4 2- from the salt
• H+ and OH- from the water

Copper loses it's charge more readily than hydrogren

Hydroxide loses it's charge more readily than sulfate

Therefore:

• Copper is the product at the cathode
• Hydroxide ions are discharged from the anode and oxygen is produced
• Water is also produced

• Na2+ and SO4 2+ from the salt
• H+ and OH- from the water

Hydrogen ions lose there charge more readily than sodium ions

Hydroxide ions lose there charge more readily than sulfate ions

Therefore:

• Hydrogren gas is discharged at the cathode
• Oxygen gas is discharged at the anode