(i) Refer answer number 4(i).
(ii) In this method, the impure metal is made to act as anode. A strip ofthe same metal in pure form is used as cathode. They are put in a suitableelectrolytic bath containing soluble salt of the same metal. The more basicmetal remains in the solution and the less basic ones go to the anodemud.
‌‌‌Anode: :M ––––▶Mn++ne−
‌‌Cathode :Mn++ne− ––––▶M
Copper is refined using an electrolytic method. Anodes are of impurecopper and pure copper strips are taken as cathode. The electrolyte isacidified solution of copper sulphate and the net result of electrolysis isthe transfer of copper in pure form from the anode to the cathode:
‌‌Anode : Cu ––––▶Cu2++2e−
‌Cathode : Cu2++2e− ––––▶Cu
Impurities from the blister copper deposit as anode mud which containsantimony, selenium, tellurium, silver, gold and platinum; recovery ofthese elements may meet the cost of refining.
Zinc may also be refined this way.
(iii) In this method, the metal is converted into its volatile compound andcollected elsewhere. It is then decomposed to give pure metal. So, the tworequirements are:
(a) The metal should form a volatile compound with an availablereagent.
(b) The volatile compound should be easily decomposable, so that therecovery is easy.
Following example will illustrate this technique.
Mond process for Refining Nickel : In this process, nickel is heatedin a stream of carbon monoxide forming a volatile complex, nickeltetracarbonyl:
Ni+4CO

330−350 K

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Ni( CO)4
The carbonyl is subjected to higher temperature so that it is decomposedgiving the pure metal :
Ni(CO)4

450−470 K

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Ni+ 4CO