The E0 of zinc (Zn2+ / Zn=−0.76V) 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 (E0Al3+∕Al=−1.66V) , Mg (E0Mg2+∕Mg=−2.37V) , Ca(E0Ca2+∕Ca=−2.87V),K(E0K+∕K=−2.93V) 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.