(a) Give the chemical names and formulae of the main ores of

(i) aluminium,

(ii) iron and

(iii) zinc.

(b) Which impurities are present in bauxite?

(c) What is red mud, how is it removed?

In order to obtain 1 tonne of aluminium, the following inputs are required: 4 tonnes of bauxite, 150 kg of sodium hydroxide and 600 kg of graphite. The aluminium compound in bauxite is aluminium oxide and the main impurity is iron (III) oxide. Aluminium is obtained by the electrolysis of aluminium oxide dissolved in cryolite.

(a) When bauxite is treated with sodium hydroxide solution, what happens to

(i) the aluminium oxide

(ii) the iron (III) oxide

(b) (i) Name the process used for the purification of bauxite.

(ii) Write the equation for the action of heat on aluminium hydroxide.

(c) (i) Write the formula of cryolite.

(ii) Write down the word which correctly completes the following sentence:

By dissolving aluminium oxide in cryolite a …………… (conducting/non-conducting) solution is produced.

(iii) Why is so much graphite required for the electrolytic process?

(iv) Write the equation for the reaction which takes place at the cathode

(v) What is the cathode made up of?

(a) A to F below relate to the source and extraction of either zinc or aluminium:

A. Bauxite

B. Coke

C. Cryolite

D. Froth floatation

E. Sodium hydroxide solution

F. Zinc blende

(i) Write down the three letters each from the above list which are relevant to

1. Zinc
2. Aluminium

(ii) Fill in the blanks using the most appropriate words from A to F.

1. The ore from which aluminium is extracted must first be treated with …………… so that pure aluminium oxide can be obtained.

2. Pure aluminium oxide is dissolved in …………… to make a conducting solution.

(iii) Write the formula of cryolite.

Explain with reasons:

In the electrolytic reduction of alumina, the graphite anode is gradually consumed.

or

Why the anode has to be replaced from time to time in this process?