Question

Calculate the vapor pressure of a solution prepared by dissolving 0.50mol of nonvolatile solute in 275g of hexane (molar mass=86.18g/mol) at 49.6C. (The vapor pressure of pure hexane at 49.6C is 400.0 mmHg)

Answer 1

Ans

The vapour pressure of a solution of a non-volatile solute is equal to the vapour pressure of the pure solvent at that temperature multiplied by its mole fraction.

P = X solv • P°solv

Calculaye for Num of mole of hexane

Num of mole of hexane = 275/86.18 =3.19 moles

We have already given mole of solute= 0.50 mole

Total number of mole = 3..19 + 0.50 = 3.69 mole

Mole fraction of solvent X solv = moles of solvent / total number of moles

Mole fraction of solvent X solv = 3.19 /3.69

Mole fraction of solvent X solv = 0.864

P°solv   = 400 mmhg

P = X solv • P°solv  

P = 0.864 x 400

P= 345.6 mmhg

So vapour pressure of solution is 345.6 mmhg.