Explain in why on addition of 1 mole of NaCl to 1L of water, the boiling point of water increases, while addition of 1 mole of methyl alcohol to 1 L of water decreases its boiling point .

Explanation

NaCl is non-volatile solute. So, its addition to water lowers the vapour pressure of the water. Hence, boiling point increases. Whereas methyl alcohol is more volatile than water. So, its addition to water increases the total vapour pressure over the solution. It results in the decreases of boiling point.