Chemistry [2 Mark Question Answer]

(a) Roasting : The process of strongly heating the ore in excess of air is called roasting.
(b) Objectives achieved during the roasting of ore : In addition to all the objectives achieved during calcination, it oxidises sulphide ores to oxide ores.

Importance of calcination : (i) It removes moisture from ore (ii) It makes the ore porous (iii) It expels volatile impurities (iv) It decomposes carbonate ores to their oxides (v) It removes water of crystallization from their hydrated salts.

(i) Froth floatation
(ii) Gravity process/Hydraulic washing

Metallurgy : The different processes involved in the extraction of pure metals from their ores are collectively called metallurgy.
Any metallic or non-metallic compounds occurring in nature is called a mineral, whereas a metallic mineral, from which a metal can be profitably extracted, is called an ore.

(i) Malleability (ii) Cryolite

(i) Powdered coke prevents burning of carbon anodes and prevents heat loss from the molten electrolyte.
(ii) Zinc ion is lower in electrochemical series. Thus, carbon monoxide provides enough energy and hence, reduces zinc oxide to zinc. Aluminium ion is higher in electrochemical series. The carbon monoxide does not produce enough energy and hence aluminium oxide is not reduced to aluminium.

(i) 1. Cryolite (Na₃AlF₆) : It increases the conductivity of mixture and lowers the m.p. of electrolyte from 2050°C to 950°C.
2. Fluorspar (CaF₂) : It increases mobility of ions in the mixture as it acts as solvent for alumina and cryolite.
(ii) Powdered coke prevents (i) heat loss from the electrolyte (ii) burning of electrodes projecting out electrolyte.