Explain why `Cu^(+)` ion is not stable in aqueous solutions.

Explanation

In aqueous solution, stability of `Cu^(2+)` ion is greater than that of `Cu^(+)` ion. This is due to the fact that the hydration enthalpy (i.e., the energy evolved in hydration process) of `Cu^(2+)` ion is much greater than that for `Cu^(+)` ion, and it more than compensates for the large value of second ionisation enthalpy of copper. In fact, most of the Cu(I) - compounds undergo disproportionation in aqueous solution.
`2Cu^(+)(aq)to Cu^(2+)(aq)+Cu(s) darr`