Question

When a chalk stick is immersed in water, bubbles are emitted. Why?

Answer 1

Hint: Chalk is made up of an infinite number of fine pores of varying size which are interconnected.

Complete step by step answer:
Chalk is composed mainly of Calcium Carbonate .It is a porous substance with a large number of pores filled with air in its dry state. When a chalk is immersed in the water, the water enters into these capillaries due to the capillary action of the water, the air gets displaced from these pores which results in the formation of air bubbles in the water. Also, from the definition of chemical reaction, calcium carbonate (CaCO₃) of chalk reacts with water (H₂0) leading to the formation of air bubbles due to the evolution of carbon dioxide gas (CO₂).
Additional information:
(1) Chalk is a soft, white, sedimentary carbonate rock formed underwater, generally on the sea bed.
(2) When a chalk is dipped in water and applied on a surface, the colour gets more intense and brighter than if it were in its dry state.
(3) Chalk does not dissolve in water due to the stronger force of attraction between calcium and carbonate ions as compared to the ions of calcium carbonate and water.
(4) Chalk dissolves faster in the solution of vinegar.

Note: Due to the capillary action, the water moves in all the directions inside the chalk and the air bubbles get evolved. In water the air bubbles behave like a concave lens as the refractive index of water is more than air.