Question

How many of the below compounds are white in colour as well as soluble in water.
(i) $ {\text{CuCl}} $
(ii) $ {\text{CuC}}{{\text{l}}_{\text{2}}} $
(iii) $ {\text{KI}} $
(iv) $ {{\text{I}}_{\text{2}}} $
(v) $ {{\text{I}}_{\text{2}}}{\text{ in KI}} $
(vi) $ {\text{KN}}{{\text{O}}_{\text{3}}} $

Answer 1

Hint :The colour of chemicals is a physical property of chemicals that is caused by the excitation of electrons in most of the cases. The colour depends on the energy absorbed by the chemical. White compounds look white because when light falls on them, it gets scattered at all angles without being absorbed.

Complete Step By Step Answer:
 $ {\text{CuCl}} $ is called cuprous chloride and it is the lower chloride of the element copper. It is a white solid and it is insoluble in water. $ {\text{CuC}}{{\text{l}}_{\text{2}}} $ is blue in colour and it is soluble in water. $ {\text{KI}} $ is white in colour and it is soluble in water. Iodine is violet in colour and is insoluble in water because water is extremely polar in nature whereas iodine is diatomic and is nonpolar. Iodine in $ {\text{KI}} $ is brown in colour and it is soluble in water. Potassium nitrate is white in colour and is soluble in water.
Therefore, two of the above compounds are white in colour as well as soluble in water.

Note :
When photons having sufficient energy strike molecules, the electrons move up an energy level or two. When an electron goes to another energy level, it wants to get back to its ground state. This is achieved by losing energy in the form of photons. Through some steps, the molecule will emit a photon of a single wavelength. If the emitted photon falls in the visible region, we can see it as a colour. The colour of the molecule varies for different wavelengths.