Q. 205.0( 2 Votes )
Describe the role
(i) Gold is treated with a dilute solution of NaCN in the presence of air. Au is oxidized to Au+ which thenn combines with CN- ions to form its soluble complex.
Thus, the role of NaCN in the extraction of gold from its ore is that it helps in the formation of a soluble complex.
(ii) Role of cryolite in the extraction of aluminium from pure alumina are the following:
⇒ Cryolite lowers the melting point of alumina.
⇒ It acts as a solvent for alumina.
⇒ Cryolite makes alumina a good conductor of electricity.
⇒ It also reduces the cost of the whole process.
(iii) Impure nickel is heated in a current of CO at 330-350K, it forms a volatile nickel tetracarbonyl complex leaving behind the impurities.
The nickel tetracarbonyl thus obtained is then heated to a higher temperature when it undergoes thermal decomposition giving pure nickel.
The reaction is:
Thus, the role of CO is that it forms a volatile complex with nickel which is further decomposed to give pure nickel.
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