Question

The vapour pressure of pure water is 12.3 Kpa at 300 Kelvin find the vapour pressure of solution containing 1 molal non volatile solute..

Options are: i) 12.9KPa, ii) 11.17KPa, iii) 11.71KPa, iv) 12.17KPa, v) 12.71KPa​

Answer 1

For non- volatile solute vapour pressure of solution = P = Ppure *mole fraction of solvent
= 12.3*55.6/1+55.6 Kpa
= 12.3*0.9 Kpa
=11.17 Kpa

Here , non volatile solute is 1 molal
Means 1 mole of solute in 1 kg of solvent
So, moles of solvent = 1000/18 = 55.6
Moles of solute = 1
Thus mole fraction of solvent = 55.6/1+55.6



Hope it helps.