Question

(a) What is meant by Corrosion? Name any two methods used for the prevention of corrosion.
(b) Suppose you have to extract metal M from its enriched sulphide ore. If M is in the middle of the reactivity series, so write the various steps used in extracting this metal.

Answer 1

Hint: Corrosion is an effect of oxidation reaction. It is the process in which metal when in contact with oxygen, water vapour and acid for a long time, gets corroded and forms a layer of compound on its surface which has a distinctive colour. This process is also referred to as the eaten up of metal by the action of air, vapour or chemicals.

Complete answer:
(a) Corrosion is a process when a layer of coloured substance is formed on the metal surface when metal is kept in open air for a long time and it reacts with oxygen, water vapour and chemicals present in the surrounding.
The two methods used for prevention of corrosion are galvanizing and electroplating.
(b) M is present in the middle of the reactivity series, which means that it is moderately reactive. The steps involved to extract to form its enriched sulphide ore are:
(1) Concentration of ore: Sulphide ore is concentrated by froth-floatation method in which gangue remains at bottom and ore is present in the froth.
(2) Roasting: The enriched sulphide ore of metal M is strongly heated in the presence of air and it is converted into metal oxide.
 $ 2MS + 3{O_2} \to \;2MO + 2S{O_2} $
(3) Reduction: The metal oxide obtained is converted to metal ‘M’ by reducing agents like carbon.
 $ MO + C \to \;M + CO $
(4) Electrolytic Refining: The impure metal obtained undergoes purification. The process for purifying impure metal is called refining.

Note:
The other processes for the concentration of ores are froth floatation method, leaching, hydraulic washing and magnetic separation while other methods for the refining process are Mond process, Van arkel method, electrolytic refining, distillation vapour phase refining and zone refining.