Question

Determine the vapor pressure in torr of the solution when 43.78 g of a non-volatile, non-electrolyte substance X with molar mass of 210 g is dissolved at in 100 g of ethanol at 298K. Please note that ethanol has a molar mass of 46.07 g/mol and vapor pressure of 58.9 torr at 298K.

Answer 1

Answer:

The vapor pressure in torr of the solution is 53.7

Explanation:

Vapor pressure lowering is the colligative property that is solved with this formula:

ΔP = P° . Xm

ΔP = Vapor pressure of pure solvent (P°) - vapor pressure of solution

Xm = mole fraction for solute.

Let's solve the mole fraction (moles of solute / total moles)

Total moles = moles of solute + moles of solvent

Moles of solute = 43.78 g / 210 g/mol = 0.208 moles

Moles of solvent = 100 g / 46.07 g/mol = 2.17 moles

Total moles = 2.17 mol + 0.208 mol → 2.378 moles

Mole fraction for solute = 0.208 / 2.378 = 0.087

Let's replace the data in the main formula.

P° = 58.9 Torr

Xm = 0.087

ΔP = P° . Xm

58.9 Torr - Vapor pressur of solution = 58.9 Torr . 0.087

Vapor pressure of solution = - (58.9 Torr . 0.087 - 58.9 Torr)

Vapor pressure of solution = 53.7 Torr