Question

How would we differentiate calcium chloride, and copper sulfate?

Answer 1

Dissolve a bit of both powders in water. `CuSO_4` will give a beautiful blue colour.

Explanation:

`CuSO_4` is a white solid (a residue of water will probably give a faint blue colouration). Dissolution in water gives `[Cu(OH_2)_6]^(2+)`, which gives a characteristic blue colour in solution; this is truly one of the most beautiful colours you can see.

On the other hand, calcium chloride, a pure white powder (or colourless crystals) will give a colourless solution. Why the difference in colour? `Cu^(2+)` possesses `d` electrons, whose transitions give rise to the colour.