What happens to the vapour pressure when volatile solute is dissolved in solution and non volatile solute is dissolved in solution?

A non-volatile solute particle lowers the vapour pressure of solvent because solute particles become surrounded by solvent particles when dissolved. This causes the particles of solvent to evaporate less because it requires more energy for the particles to do this since the solvent to solute attraction are strong. So the vapour pressure of a solution is less than that of the pure solvent.

Vapour pressure depends on

Nature of liquid
Temperature
Presence of impurities

Economics 11 Notes - Apr 8 '12

Vapour pressure of pure water at 298 K is 23.8 mm. 50 g of urea (NH2CONH2) is dissolved in 850 g of water. Calculate the vapour pressure of water for this solution and its relative lowering.

Vapoure pressure of pure water (solvent) at 298 K, p0 = 23.8 mmVapour pressure of solution, p = ?Mass of solvent ,W = 850 gMass of solute,M = 50 g

Mol. mass of water (H2O), M = 18 g mol–1
Mol.mass of urea NH2 CO NH2
= 14 + 2 + 12 + 16 + 14 + 2

= 60 g mol–1
According to Raoult's law, p0-pp0=ωMWm

p=p0-w×Mm×W×p°

p=23.8-50×1860×850

=23.8-0.017=23.78

Hence, 23.78 mm Hg. Ans.

What happens to the vapour pressure when a volatile solute dissolves in the liquid b the dissolved solute is non volatile

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