Some standard electrode (or reduction) potentials in acidic solutions are as follows:
`Cu^(2+)//Cu =0.34 V, Ag^(+)//Ag=0.80V`
Predict whether the following reactions occur:
(i) Will copper(s) reduce `Ag^(+)` ion in aq. solution ?
(ii) Will copper(s) dissolve in 1 MHCl?

Explanation

A reaction is feasible if e.m.f. for the cell reaction is positive.
e.m.f. = Reduction potential of the electrode at which reduction takes place-Reduction potential of the electrode at which oxidation takes place.
(i) For the reaction, `Cu(s) +2Ag^(+) to Cu^(2+) +2Ag`
e.m.f `=0.80V-0.34V=0.46V`
As the e.m.f. for the reaction is positive, therefore, Cu(s) will reduce `Ag^(+)` ion in aqueous solution.
(ii) For the reaction
`Cu(s) +2HCl to CuCl_(2) +H_(2)`
or `Cu(s) +2H^(+) to Cu^(2+) +H_(2)`
e.m.f `=0.0V-0.34V= -0.34V`
As the e.m.f is negative for the reaction, therefore, Cu(s) will not dissolve in 1 MHCl.