Practice question
Question
The vapor pressure of pure water is 25 mm Hg at a certain temperature. A solution with a non-volatile solute has a vapor pressure of 23 mm Hg. If the solute’s molar mass is 60 g/mol, what is the mass of solute in 180 g of water?
Explanation
(p⁰ - p/p⁰) = xsolute . (25 - 23/25) = 0.08 . Moles of water = (180/18) = 10 . xsolute = (nsolute/nsolute + 10) = 0.08 . nsolute = 0.08 (nsolute + 10) , nsolute - 0.08 nsolute = 0.8 , 0.92 nsolute = 0.8 , nsolute ≈ 0.8696 . Mass = 0.8696 × 60 ≈ 52.18 g .