Write the name and principle of the method used for refining of (a) Tin, (b) Copper, (c) Nickel.

(a) Name of method used for refining of tin is Liquation. This method is suitable for low melting metals like tin. In this the impure metal is heated on a sloping hearth so that pure metal melts and flows down leaving behind high melting impurities.

(b) Name of method used for refining of Cu is electrolytic refining. This method is based on the difference in standard electrode potential. Here, the cathode and anode are pure Cu strip and impure Cu respectively and both are immersed in CuSO₄/H₂SO₄ solution. On passing current pure Cu from anode deposits on cathode whereas the impurities settle down under anode.

Cathode: Cu → Cu²⁺ + 2e^-

Anode: Cu²⁺ + 2e^- → Cu

(c) Name of method used for refining of Ni is Mond’s process. In this process crude Ni is heated in a stream of CO to form volatile nickel carbonyl. That nickel carbonyl is then subjected to high temperature to get pure Ni.

Ni + 4 CO ^{330-350 K} → Ni(CO)₄

Ni(CO)₄^{450-470 K} → Ni + 4 CO