Electrolysis

Question 1

What is the purpose of electrolysis?

Answer 1

To reverse ionic bonding

Question 2

What charges are the cathode and the anode?

Answer 2

Cathode = Negative
Anode = Positive

Named after the charges they attract

Question 3

Explain how electrolysis forms a complete circuit

Answer 3

• Anode and Cathode are connected to a power supply
• Solution of molten ionic compound has free moving ions : ions are charged particles and their movement creates a current

Question 4

Electrolysis of molten ionic Compounds (MELTS)

Answer 4

• Uses inert electrodes (normally graphite)
• Compound exists in a state of free-moving ions

Question 5

Industrial Electrolysis (Extraction of Al)

Answer 5

• Anode = Graphite “lid”
• Cathode = Graphite “tub”
• Inside “tub” is Al2O3 + Cryolite (which lowers MP)
• Large p.d in circuit

Question 6

When are Reactive and Inert electrodes used?

Answer 6

Reactive = Electroplating
Inert = Splitting ionic solutions

Question 7

Electrolysis at Inert electrodes (Copper Sulphate example)

Answer 7

Cathode:
• Competition between Cu ions and H ions from solution to react with Sulphate
• Winner is more reactive element, which stays in solution
• Less reactive element forms via reduction at cathode

Anode:
• Competition between anions (Hydroxide vs Sulphate)
• Hydroxide will always be oxidised out if solution unless halide is present
(this means hydroxide will split and form oxygen at anode)

Halides = Group 7

Question 8

Electroplating

Answer 8

Anode = Reactive Metal electrode (eg. Copper)
Cathode = Object being covered in metal

• Anode will release metal ions that will form at cathode (plating the cathode)