The rate of evaporation decreases when common salt is added to water ? Why
Answers
Answer:
When a non-volatile solute that is salt is added to a solvent that water, the vapour pressure of the resulting solution (salt solution) is less than the vapour pressure above the pure solvent (water). Thus rate of evaporation decreases.
This happen so because the surface of a pure solvent is populated only by solvent molecules. Some of these molecules are escaping from the surface, and others are returning to the liquid state. The surface of a solution is populated by two kinds of molecules; some are solvent molecules,others are solute molecules. Only the solvent molecules are volatile. They alone can escape to build up the vapour pressure of the solution. There are fewer solvent molecules on the surface of the solution than on the surface of the pure liquid. Fewer will vaporise and, as a consequence, the vapour pressure of the solution will be less than that of the pure liquid at the same temperature. Hence, rate of evaporation decreases.