Some Basic Principles Of Organic Chemistry Question 229
Question: In which of the following pair of metals, both are commercially extracted from their respective ores by self- reduction method?
Options:
A) Zn, Cu
B) Pb, Cu
C) Sn, Zn
D) Al, Ag
Show Answer
Answer:
Correct Answer: B
Solution:
(i) Extraction of tin (carbon reduction): $ SnO_2+2C\to Sn+2CO $
(ii) Extraction of zinc (carbon reduction): $ ZnO+C\xrightarrow{coke,673}Zn+CO $
(iii) Extraction of lead (self-reduction): $ PbS+2O_2\to PbSO_4; $
$ PbS+3O_2\to 2PbO+2SO_2 $
$ PbS+2PbO\to 3Pb+SO_2; $
$ PbS+PbSO_4\to 2Pb+2SO_2 $
(iv) Extraction of copper (self-reduction): $ 2CuFeS_2+4O_2\to Cu_2S+2FeO+3SO_2 $
$ Cu_2S+FeO+SiO_2\to FeSiO_3 $
$ (fusible,slag)+Cu_2S(Matte) $
$ 2Cu_2S+3O_2\to 2Cu_2O+2SO_2; $
$ 2Cu_2O+Cu_2S\to 6Cu+SO_2 $
(v)Extraction of aluminium (electrolytic reduction, Hall- Heroult process): The purified $ Al_2O_3 $ is mixed with $ Na_3AlF_6 $ (cryolite) or $ CaF_2 $ , (fluorspar) which lowers the melting point of the mixture and increases conductivity.
The fused matrix is electrolysed.
Cathode: $ A{{l}^{3+}} $ (melt) + $ 3{{e}^{-}}\to Al,(l) $
Anode: $ C(s)+{{O}^{2-}} $ (melt) $ \to CO(g)+2{{e}^{-}} $ $ C(s)+2{{O}^{2-}}(melt)\to CO_2(g)+4{{e}^{-}} $
(vi) Extraction of gold/silver (leaching and displacement method): $ 4Au/Ag(s)+8C{{N}^{-}}(aq)+2H_2O(aq)+O_2(g) $
$ \to 4{{[Au/Ag{{(CN)}_2}]}^{-}}(aq)+4O{{H}^{-}}(aq) $
$ 2{{[Au/Ag{{(CN)}_2}]}^{-}}(aq)+Zn(s)\to 2Au/Ag(s) $
$ +{{[Zn{{(CN)}_4}]}^{2-}}(aq) $
