. State the principle on which each of the following processes operates


State the principle on which each of the following processes operates

(i) Recovery of silver after the silver ore has been leached with NaCN.

(ii) Electrolytic refining of a metal.

(iii) Vapour phase refining of a metal

Best Answer

(i) Recovery of silver after silver ore was leached with NaCN: During leaching Ag is oxidised to Ag + which then combines with CN– ions to form soluble complex, [Ag(CN)2 ] – . Silver is then recovered from this complex by displacement method using more electropositive zinc metal

 electropositive zinc meta

(ii) Electrolytic refining of a metal: In this method, the impure metal is made to act as anode. A strip of same metal in pure form is used as cathode. They are put in a suitable electrolytic bath containing soluble salt of same metal. When electric current is passed the metal from the anode goes into solution as ions due to oxidation while pure metal gets deposited at the cathode due to reduction of metal ions. The voltage applied for electrolysis is such that impurities of more electropositive metals remains in the solution as ions while impurities of the less electropositive metals settle down under the anode as anode mud.

Electrolytic refining of a metal

(iii) Vapour phase refining of a metal: In this method, the metal is converted into its volatile compound and collected elsewhere. It is then decomposed to give pure metal. For example, refining of nickel by Mond process.

Vapour phase refining of a metal

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