# What occurs when copper(II) oxide is treated with sulfuric acid?

$C u O \left(s\right) + {H}_{2} S {O}_{4} \left(a q\right) \rightarrow C {u}^{2 +} + S {O}_{4}^{2 -} + {H}_{2} O$
The $C {u}^{2 +}$ ion in water (probably $C u {\left(O {H}_{2}\right)}_{6}^{2 +}$) gives a truly beautiful blue colour, from which large macroscopic crystals can be obtained.