For a binary solution, when a nonvolatile nonelectrolyte solute is dissolved in solvent, the vapour pressure of solvent decreases by 20 % . what is mole fraction of solvent in solution ?

Step-by-step solution

Let the vapour pressure of the pure solvent be P^0 . The decrease in vapour pressure is given as 20 % , so the lowering of vapour pressure is P = 0.20 P^0 . According to Raoult's law, the relative lowering of vapour pressure is equal to the mole fraction of the solute, X_ solute . P P^0 = X_ solute X_ solute = 0.20 P^0 P^0 = 0.20 For a binary solution, the sum of mole fractions of solute and solvent is 1 . X_ solvent = 1 - X_ solute X_ solvent = 1 - 0.20 = 0.8 Answer: 0.8