Take a small amount of hydrochloric acid in a test tube. Heat the test tube. Dip a glass rod in the ammonia solution and hold on the top of the test tube. You will observe a white smoke emanating from the tip of the glass rod. Why?

On heating, HCL vapours emanate from the test tube and NH3 gas is generated from the solution on the glass rod. The ammonia gas and hydrogen chloride gas react together to form the salt ammonium chloride in gaseous state first. However, immediately because of the condensation process at room temperature, it is converted into a solid state, thus causing the white smoke. The chemical equation for this is as follows.

NH3 (g)+ HCl(g) ➡NH4Cl(s)

Ammonia + Hydrogen chloride ➡Ammonium chloride