Question
A. 10.0 g sample of the solid sucrose ( sugar, C12H22O11) was dissolved in 200.0 g of water. What will the vapor pressure of this solution be at 25C, if the normal vapor pressure of pure water at 25C is 23.8 torr?

B. Predict the vapor pressure of a solution prepared by dissolving 49.4 g of solid calcium chloride, CaCl, in150 g of water at 25C. The vapor pressure of water at 25C is 23.8 torr.

A. Vapor Pressure depression of glucose solution

Amount of the sugar present = 10.0g/ (342) = 0.0292397661 mol
Amount of water present = 200g/ (18) = 11.11111111 mol

Thus, X(H2O), which signifies the fraction of water present,
= 11.11111111/ (11.11111111 + 0.0292397661)
= 0.9973753281

At 25 deg Celsius,
Vapor Pressure of Water is then = 0.9973753281 x 23.8
= 23.73753281 Torr.

B. Vapor pressure of CaCl2 solution

Amount of Calcium Chloride = 49.4g/ (40.1) = 1.2319202 mol
Amount of water = 150g/ (18) = 8.333333333 mol

Thus, X(H2O), which signifies the fraction of water present,
= 8.333333333/ (8.333333333 + 1.2319202 )
= 0.8712088294

Vapor Pressure of Water is then = 0.8712088294 x 23.8
= 20.73477014 Torr.