A) Zn, Cu
B) Pb, Cu
C) Sn, Zn
D) Al, Ag
Correct Answer: B
Solution :
[b]| (i) Extraction of tin (carbon reduction): |
| \[Sn{{O}_{2}}+2C\to Sn+2CO\] |
| (ii) Extraction of zinc (carbon reduction): |
| \[ZnO+C\xrightarrow{coke,673}Zn+CO\] |
| (iii) Extraction of lead (self-reduction): |
| \[PbS+2{{O}_{2}}\to PbS{{O}_{4}};\] |
| \[PbS+3{{O}_{2}}\to 2PbO+2S{{O}_{2}}\] |
| \[PbS+2PbO\to 3Pb+S{{O}_{2}};\] |
| \[PbS+PbS{{O}_{4}}\to 2Pb+2S{{O}_{2}}\] |
| (iv) Extraction of copper (self-reduction): |
| \[2CuFe{{S}_{2}}+4{{O}_{2}}\to C{{u}_{2}}S+2FeO+3S{{O}_{2}}\] |
| \[C{{u}_{2}}S+FeO+Si{{O}_{2}}\to FeSi{{O}_{3}}\] |
| \[(fusible\,slag)+C{{u}_{2}}S(Matte)\] |
| \[2C{{u}_{2}}S+3{{O}_{2}}\to 2C{{u}_{2}}O+2S{{O}_{2}};\] |
| \[2C{{u}_{2}}O+C{{u}_{2}}S\to 6Cu+S{{O}_{2}}\] |
| (v)Extraction of aluminium (electrolytic reduction, Hall- Heroult process): |
| The purified \[A{{l}_{2}}{{O}_{3}}\] is mixed with \[N{{a}_{3}}Al{{F}_{6}}\] (cryolite) or \[Ca{{F}_{2}}\], (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)\[\to CO(g)+2{{e}^{-}}\] |
| \[C(s)+2{{O}^{2-}}(melt)\to C{{O}_{2}}(g)+4{{e}^{-}}\] |
| (vi) Extraction of gold/silver (leaching and displacement |
| method): |
| \[4Au/Ag(s)+8C{{N}^{-}}(aq)+2{{H}_{2}}O(aq)+{{O}_{2}}(g)\]\[\to 4{{[Au/Ag{{(CN)}_{2}}]}^{-}}(aq)+4O{{H}^{-}}(aq)\] |
| \[2{{[Au/Ag{{(CN)}_{2}}]}^{-}}(aq)+Zn(s)\to 2Au/Ag(s)\]\[+{{[Zn{{(CN)}_{4}}]}^{2-}}(aq)\] |
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