For each of the substance listed below. Describe the role played in the extraction of aluminium.
(1) Cryolite:
(2) sodium hydroxide
(3) Graphite
(1) Cryolite: to reduce the melting point of alumina and increase the conductivity of the solution.
(2) sodium hydroxide: for purification of bauxite ore as a leaching agent.
(3) Graphite: As anode and make the reduction of Al2O3 easier.