Question

Which of the metals any easy and b are extracted by complex formation reduction with carbon electrolysis of fused

Answer 1

Electrolytic reduction : The oxides of the highly electropositive metals like Na, K, Mg, Ca, Al, etc., cannot be reduced easily with carbon at moderate temperatures. For reduction, a very high temperature is required at which the metal may combine with carbon to form a carbide. These metals are thus extracted by the electrolysis of their oxides, hydroxides or chlorides in fused state. Sometimes, a small amount of some other salt is added as to lower the fusion temperature or to increase the conductivity or both. The metal is liberated at the cathode. Sodium is obtained by the electrolysis of fused mixture of NaCl and CaCl2 (Down’s process) or by electrolysis of fused sodium hydroxide (Castner’s process). 




(d) Hydrometallurgy : This process is based on the fact that more electropositive metal can displace less electropositive metal from its salt solution. The ore is teated with such chemical reagents which convert it into soluble compound. By the addition of more electropositive metal to the filtrate, the metal present in the ore can be precipitated. The following two examples illustrate this process.

(i) Extraction of copper : Malachite ore is first roasted.

CuCO3·Cu(OH)2  2CuO + H2O + CO2

Copper oxide obtained is dissolved in sulphuric acid.

CuO + H2SO4   CuSO4 + H2O

   (Soluble) 

To the solution of copper sulphate, scrap iron is added which precipitates copper.

CuSO4 + Fe   Cu + FeSO4

   ppt. Soluble 

(ii) Extraction of silver : The ore is dissolved in sodium cyanide solution. 

Ag2S + 4NaCN  2NaAg(CN)2 + Na2S

By the addition of zinc turnings, Ag is precipitated

2NaAg(CN)2 + Zn   Na2Zn(CN)4 + 2Ag

   Solubleppt.