Question

What do you observe when water droplets fall on white copper sulphate.

Answer 1

The white copper sulphate is known as anhydrous copper sulphate as it does not contain any water molecule. But when water droplets fall over this white anhydrous copper sulphate the color of copper sulphate changes from white to blue.

Complete Answer:
The copper sulphate $\left( {CuS{O_4}} \right)$ is generally white in colour. This is also known as anhydrous copper sulphate. Here $C{u^{ + 2}}$ forms an ionic bond with sulphate ion. When we add water molecules there is a change of colour of the copper sulphate. When water molecules are added to the anhydrous copper sulphate then $C{u^{ + 2}}$ ion makes a co-ordinate bond with some of the water molecules. While some of the water molecules make a complex with the copper sulphate. Now the colour of the copper sulphate changes from white to blue. Now these crystals become blue in colour. This is because of the complex formed with the water molecules. Also after adding water droplets the anhydrous copper sulphate becomes hydrous copper sulphate. Also generally copper acquires water molecules in the ratio of $1:5$. Therefore five moles of water will be making a complex compound with the anhydrous copper sulphate. This can be represented as,
${\text{CuS}}{{\text{O}}_{\text{4}}}{\text{ + 5 }}{{\text{H}}_{\text{2}}}{\text{O }}\xrightarrow{{}}{\text{ }}{\left[ {{\text{Cu}}{{\left( {{H_2}O} \right)}_5}} \right]^{2 + }}{\text{ + S}}{{\text{O}}_4}^{2 - }$

Note:
The reason for the change in colour of hydrated copper sulphate is the presence of oxygen atoms around the copper atom. Also when water droplets are added to anhydrous copper sulphate the reaction is exothermic in nature. Thus the energy released during the reaction. Thus the addition of water molecules changes the electronic energy of water which in turn gives the blue colour of the crystals of copper sulphate.