Question

Why is CuI2 unstable?

Answer 1

`CuI_2` will have a redox reaction

Explanation:

If we bring together `Cu^(2+)` and `I^-` ions the copper(II) will be reduced to copper(I), while part of the iodide will be oxidized to iodine.
Copper(I)iodide is badly soluable:

`2Cu^(2+)(aq)+4I^-(aq) -> 2CuI(s)+I_2(aq)`

The partial reactions being:
`2Cu^(2+)(aq)+2e^(-) ->2Cu^+(aq)` = reduction
`2I^(-)(aq) ->I_2(aq)+2e^-` = oxidation
`2Cu^+(aq) +2I^(-)(aq)->2CuI(s)` = precipitation