Calculate the vapor pressure of a solution? CHEMISTRY - Please check my answers??!!

Question

Calculate the vapor pressure of water above a solution made by adding 15.0 g of lactose (C12H22O11) to 100.0 g of water at 338 K. (vapor pressure of pure water at 338 K is 187.5 torr)

P (vapor pressure of solution) = X (mole fraction of compound a) * P (normal vapor pressure of a at that temp)

15.0 g lactose (1mol / 342.34 g) = 0.043816083 mol lactose
100.0 g h20 (1 mol / 18.02 g) = 5.549389567 mol H2O

mole fraction of water = 5.5493 mol H2O / (5.5493 + 0.04381)mol = 0.992 mol H2O

P = (0.992 mol H2O) * (187.5 torr) = 186 torr


Is this right or completely wrong? Thanks for the help!!!

Answer 1

Your steps are correct.

 

Basically, you used the Raoult's Law formula (used when non evaporating solutes are added to solvents).