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NCERT Class XII Chemistry
Chapter - General Principle of Process of Isolation of Elements
Questions with Solutions

Question : 1
Total: 31
The E0 of zinc ( Zn2+ / Zn =0.76 V ) is lower than that of copper (Cu2+ / Cu =+0.34V ). Hence, zinc can displace Cu from solutions of Cu2+ ions.
Zn( s)+ Cu2+(aq) Zn2+(aq)+ Cu(s)
But to displace zinc from solution of Zn2+ ions, we need a metal more Al reactive than it, i.e, Al (E0 Al3+Al=1.66 V ) , Mg (E0 Mg 2+Mg=2.37 V ) , Ca(E0Ca2+Ca=2.87 V ), K(E0 K +K=2.93 V ) etc.
But all these metals react with water forming their corresponding ionswith the evolution of H2 gas. Hence, Al, Mg, etc. cannot be used todisplace zinc from the solution of Zn2+ ions. Thus, copper can be extractedby hydrometallurgy but notzinc.
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