Question

When a chalk stick is dipped in ink, then

• A. The coloured pigments in the ink get absorbed in the chalk
• B. The solvent got adsorbed at the surface of chalk
• C. Inside of the chalk will remain as white while the surface will have coloured pigment
• D. Inside of the chalk will have coloured pigments while the surface will remain white.

Answer 1

The correct option is C Inside of the chalk will remain as white while the surface will have coloured pigment

Adsorption:
The substance is concentrated only at the surface and does not penetrate through the surface to the bulk of the adsorbent.

Absorption:
The substance is uniformly distributed throughout the bulk of the solid.

When both absorption and adsorption, of the same substance, take place simultaneously, it is called sorption.
Example: Chalk in ink solution

When a chalk stick is dipped in ink, the surface retains the colour of ink due to adsorption of coloured molecules while solvent of ink goes deeper and distributes throughout the chalk due to absorption.
Since, the colour pigment is only present on surface, the inside of chalk remains white.