Topic 4 - Extracting Metals and Equilibria

Question 1

How is the process of extracting aluminium from aluminium oxide by electrolysis made cheaper?

Answer 1

The aluminium oxide is dissolved in molten cryolite to bring the melting point down from 2000C to about 900C.

This saves energy, making the process cheaper and easier.

Question 2

What occurs during the electrolysis of

aluminium oxide?

Answer 2

The positive aluminium ions are attracted to the cathode where they are reduced and turn into neutral aluminium atoms. These sink to the bottom of the electrolysis tank.
The negative oxygen ions are attracted to the anode where they are oxidised and turn into neutral oxgen atoms. These combine to form O2 molecules. Some of the oxygen produced reacts with the carbon in the electrode to produce carbon dioxide.

Question 3

What is the equipment for

electrolysing aluminium oxide?

Answer 3

• a tank
• a graphite lining around the tank which acts as a cathode
• graphite anodes placed inside the tank