8.9: Explain why Cu+ ion is not stable in aqueous solutions?

In an aqueous medium, Cu2+ is more stable than Cu+. This is because although energy is required to remove one electron from Cu+ to Cu2+, high hydration energy of Cu2+ compensates for it. Therefore, Cu+ ion in an aqueous solution is unstable. It disproportionates to give Cu2+ and Cu.
2Cu(aq) Cu2+(aq) + Cu(s)