Calculate the vapor pressure, in mm hg, at 25c of water above a solution made by dissolving 100. g sucrose, (fw = 342.3) in 250. g of water. the vapor pressure of pure water at 25c is 23.8 mm hg.

We need two pieces of information to calculate the reduction of the vapor pressure of the solvent in a solution containing a nonvolatile nonelectrolyte:

The mole fraction of the nonvolatile solute, Xsolute, in the solution. The vapor pressure of the pure solvent, Psolv.

Psoln = Psolvent (1 - Xsolute)

Xsolute = (100g / 342.3 g / mol) / (100g / 342.3 g / mol) + (250 g / 18 g / mol)

X solute = 0.0206

P soln = (23.8 mmHg) (1 - 0.0206)

Psoln = 23.31 mmg Hg