Question

The vapour pressure of water is 12.3 kPa at 300 K. Calculate vapour pressure
of 1 molal solution of a non-volatile solute in it​

Answer 1

Answer:

The vapour pressure of water is 12.3 kPa at 300 K. We need to calculate the vapour pressure of 1 molal solution of a non-volatile solute in it.

1000 g of water contains 1 mole of solute.

The molar mass of water is 18 g/mol.

Number of moles of water =

18

1000

=55.56 mol

Mole fraction of the solute in the solution is x=

1+55.56

1

=0.0177.

The relative lowering in the vapour pressure is equal to the mole fraction of solute.

p

0

p

0

−p

=x

12.3

12.3−p

=0.0177

⇒p=12.08

Hence, the vapour pressure of the solution is 12.08 kPa.