The Total solution for NCERT class 6-12
The vapour pressure of water is12.3 kPa at 300 K. Calculate vapour pressure of 1 molal solution of anon-volatile solute in it.
1 molal solution means 1 mol ofthe solute is present in 1000 g of the solvent (water).
Molar mass of water = 18 g mol−1
= 55.56 mol
Therefore, mole fraction of thesolute in the solution is
It is given that,
Vapour pressure of water, = 12.3 kPa
Applyingthe relation,
⇒ 12.3 − p1 = 0.2177
⇒ p1 = 12.0823
= 12.08 kPa (approximately)
Hence, the vapour pressure of thesolution is 12.08 kPa.