Question

calculate the vapor pressure at 80C of a solution prepared by dissolving 0.0300 moles of glucose in 100.0g water. vapor pressure of water at 80C is 355torr. Please explain!

Answer 1

Vapour pressure of the solution = Mole fraction of solvent x pure vapor pressure of the solvent.

Calculation of mole fraction of solvent.

Mole fraction of solvent = moles of solvent / total moles

Moles of glucose (solute) = 0.0300 mol

Moles of water (solvent ) = 100.0 g x 1 mol water / 18.0148 g water = 5.55 mol H2O

(we used molar mass of water to convert mass into moles)

Mole fraction of water = 5.55 / ( 0.0300 + 5.55 ) = 0.995

Vapor pressure of the solution = mole fraction of solvent x vapor pressure of pure solvent

= 0.995 x 355 torr

= 353.1 torr

Vapour pressure of the solution would be = 353.1 torr