# Question #b39e6

Oct 19, 2016

$C {u}^{2 +} \left(a q\right)$ has a lovely blue colour.

#### Explanation:

The anhydrous salt, $C u S {O}_{4}$, is pure white. It dissolves in water to form the hexa-aqua ion, ${\left[C u {\left(O {H}_{2}\right)}_{6}\right]}^{2 +}$, whose electronic transitions gives rise to the blue colour. The sulfate ion is along for the ride.

This video shows the color change that takes place when copper (II) sulfate (blue color) is heated. The heating drives off the water and forms anhydrous copper (II) sulfate which has a white color.