Thus,the freezing point is 0.0-7.70=-7.70C (iii)Calculate the vapor pressure(mm Hg)of the solution at 25C.(The vapor pressure of pure water at 25C is 23.8 mm Hg.) In 1 L of the solution,we have 1.5 moles CaCl2 (=4.5 moles ions)and 1083.3 g H2O=1083.3/18.0=60.18 mol H20 nH.o 60.18 Xnoao"6018+4s-0930 Poh=p°aXa=23.8mmHg×0.930=22.1mmHg 8Thus, the freezing point is 0.0 – 7.70 = -7.70o C (iii) Calculate the vapor pressure (mm Hg) of the solution at 25o C. (The vapor pressure of pure water at 25o C is 23.8 mm Hg.) In 1 L of the solution, we have 1.5 moles CaCl2 (= 4.5 moles ions) and 1083.3 g H2O = 1083.3/18.0 = 60.18 mol H2O 2 2 2 H O H O H O solute 0 soln solv solv n 60.18 X 0.930 n n 60.18 4.5 p p X 23.8 mm Hg 0.930 22.1 mm Hg = == + + = = ×= 8