Question

A to F below relate to the source and extraction of either zinc or aluminium.
A. bauxite
B. coke
C. cryolite
D. froth flotation
E. sodium hydroxide solution
F. zinc blende.
(a) Write down the three letters each from the above list which are relevant to:
(i) zinc
(ii) aluminium
(b) Fill in the blanks using the most appropriate words from A to F:
(i) The ore from which aluminium is extracted must first be treated with _________ so that pure aluminium oxide can be obtained.
(ii) Pure aluminium oxide is dissolved in _________ to make a conducting solution.
(c) Write the formula of cryolite.

Answer 1

(a) The three letters from the above list that are relevant to
(i) Extraction of zinc are as follows:
D – froth floatation,
F – zinc blende
B – coke
This is because the sulphide ore of zinc is zinc blende (ZnS), which is concentrated by the froth floatation process. The zinc oxide thus obtained after the roasting process is reduced by coke to zinc metal.

(ii) Extraction of aluminium are as follows:
​ A – bauxite
C – cryolite
E– sodium hydroxide solution
This is because bauxite is the main ore of aluminium, which is purified by its reaction with a hot sodium hydroxide solution. The pure alumina thus obtained is mixed with cryolite, which is used as a solvent in the process, and helps in lowering the melting point of alumina.

(b)
(i) The ore from which aluminium is extracted must first be treated with a sodium hydroxide solution so that pure aluminium oxide can be obtained.
(ii) Pure aluminium oxide is dissolved in cryolite to make a conducting solution.

(c) The formula for cryolite is ${\mathrm{Na}}_3{\mathrm{AlF}}_6$.