Question

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

Out of Cu⁺ and Cu²⁺, which ion is unstable in aqueous solution and why?

Answer 1

\[\ce{Cu^{2+}_{ (aq)}}\] is more stable than \[\ce{Cu^{+}_{ (aq)}}\]. This is because copper has a higher second ionization enthalpy, but Δ_hydH for \[\ce{Cu^{2+}_{ (aq)}}\] is more negative than that for \[\ce{Cu^{+}_{ (aq)}}\], so it compensates more for the second ionization enthalpy of copper. Thus many copper (I) compounds are unstable in aqueous solution and are disproportionated as follows:

\[\ce{2Cu^{+}_{ (aq)} -> Cu^{2+}_{ (aq)} + Cu_{(s)}}\]