Question

Answer the following questions:
(i) Name a metal which is found abundantly in the earth's crust.
(ii) What is the difference between calcination and roasting?
(iii) Name the process used for the enrichment of sulphide ore.
(iv) Write the chemical formulae of one main ore of iron and aluminium.
(v) Write the constituents of electrolyte for the extraction of aluminium.

Answer 1

(i) A metal that is found abundantly in the earth's crust is aluminium.
(ii) The difference between calcination and roasting is given below:

Calcination	Roasting
1. The process of heating a concentrated ore in the absence of air is called calcination.	1. The process of heating a concentrated ore in the presence of air is called roasting.
2. Generally, hydrated oxides and carbonate ores are calcined.	2. Generally, sulphide ores are roasted.
3. During calcination, hydrated oxides and carbonate ores are converted to metallic oxides.	3. During roasting, sulphide ores are converted to metallic oxides, metallic sulphates or into metals.
4. Calcination removes moisture, volatile impurities and any organic matter present in the ore and makes the ore porous.	4. Roasting removes moisture, volatile impurities of P, As and S (escapes in the form of gases).
5. Calcination is carried out in a reverberatory furnace by keeping the holes in the furnace closed.	5. Roasting is carried out in a reverberatory furnace by keeping the holes in the furnace open, in order to allow air to enter the furnace.

(iii) The process used for the enrichment of sulphide ore is the froth flotation process.
(iv) The chemical formula of one main ore of iron is ${\mathrm{Fe}}_2{\mathrm{O}}_3$ (h) and that of aluminium is ${\mathrm{Al}}_2{\mathrm{O}}_3.2{\mathrm{H}}_2\mathrm{O}$ (bauxite).
(v) The constituents of the electrolyte for the extraction of aluminium are molten pure alumina (${\mathrm{Al}}_2{\mathrm{O}}_3$) mixed with
cryolite (${\mathrm{Na}}_3{\mathrm{AlF}}_6$) and fluorspar (${\mathrm{CaF}}_2$).