Copper can be extracted by hydrometallurgy but not zinc. Explain.

Explanation

The `E^(@)` of zinc `(Zn^(2+)//Zn=-0.76V)` or iron `(Fe^(2+)//Fe=-0.44V)` is lower than that of copper `(Cu^(2+)//Cu=+0.34V)`. Hence, both zinc and iron can displace copper from `Cu^(2+)` solutions. Though zinc is a stronger reducing agent, scrap iron is cheaper and hence is chiefly used in hydrometallurgy of copper.
`Fe(s)+Cu^(2+)(aq)rarr Fe^(2+)(aq)+Cu(s)`
A more reactive metal like `Al(E_(Al^(3+)//Al)^(@)=-1.66V)`,
`Mg(E_(Mg^(2+)//Mg^(@))=-2.37V), Ca(E_(Ca^(2+)//Ca)^(@)=-2.87V)`,
`K(E_(K^(+)//K)^(@)=-2.93V),` etc, are required to displace zinc from its solution. However, these metals react with water to form corresponding ions with the evolution of `H_(2)` gas.
`[2H_(2)O+2erarr H_(2)(g)+2OH^(-)(aq), E^(@)=-0.83V]`
Al, Mg, etc. cannot be used to displace Zn from its solution. Thus, Cu can be extracted by hydrometallurgy but not Zn.