Question

How does the president of important affect the boiling point and freezing point of substance?

Answer 1

EFFECT OF IMPURITY ON BOILING POINT:The boiling point of a liquid is a measure of the force of attraction between its particles.When an impurity is added to substance, its Boiling point is elevated.
Reason: The elevation[increase] in boiling point increases with the increases in concentration of the solute because on adding the solute, vapor pressure of solution becomes lower than pure solvent.Thus solution has to be heated more to make vapour pressure equal to atmospheric pressure.Example:Boiling point of water is 100⁰C  at normal atmospheric pressure. If we add salt, its vapor pressure decreases and Boiling point increases.
EFFECT OF IMPURITIES ON FREEZING POINT:When impurity is added , Its freezing point decreases.Reason:The depression in Freezing point increases with increase in concentrate of solute because on adding the solute, vapour pressure becomes  lower than that of pure solvent. Hence freezing occurs at lower temperature.Example:Freezing point of water is 0⁰C under normal atmospheric pressure. If we add salt, the freezing point decreases.