vapor pressure of solution 13.00 g of CaCl2 in 115.0 g of H2O at 70 ∘C, van't Hoff factor of 2.7? The vapor pressure of pure water at 70 ∘C is 233.7 mmHg.

Question

What is the vapor pressure in mmHg of a solution made by dissolving 13.00 g of CaCl2 in 115.0 g of H2O at 70 ∘C, assuming a van't Hoff factor of 2.7? The vapor pressure of pure water at 70 ∘C is 233.7 mmHg.

Answer 1

13.0 g CaCl₂ x 1 mole/111 g = 0.117 moles x 2.7 moles of ions/mole = 0.316 moles of ions.

moles H₂O =115.0 g x 1 mole/18 g = 6.38 moles H₂O

Total moles = 6.38 + 0.316 = 6.70 moles

Mole fraction of water = 6.38/6.70 = 0.952

Vapor pressure of solution = 0.952 x 233.7 mm Hg = 222.5 mm Hg