Calculate the vapor pressure at 35C of a solution made by dissolving 20.2g of sucrose, C12H22O11, in 60.5g of water.

Question

V.P water 35 C = 42.2 mmHg

Answer 1

The vapor pressure of the solution can be found using Raoult's Law.

P_soln = X_H2O * P_o where P_soln is vapor pressure of solution; X_H2O is mol fraction of H₂O and P₀ is vapor pressure of pure H₂O

molar mass sucrose = 342 g/mol

moles sucrose present = 20.2 g x 1 mol/342 g = 0.0591 moles

molar mass H2O = 18 g/mol

moles H2O present = 60.5 g x 1 mol/18 g = 3.36 moles

Total moles present = 0.0591 moles + 3.36 moles = 3.42 moles

mole fraction of H2O = 3.36 mol / 3.42 mol = 0.983

Vapor pressure of solution = mol fraction of H2O x vapor pressure of pure water = 0.983 x 42.2 mm Hg

Vapor pressure of solution = 41.5 mm Hg