Solution Laws

REVISION EXERCISE (SOLUTION LAWS)

1. A solution is prepared by mixing 5.81 g acetone and 11.9 g chloroform. At 35oC, this solution has a total vapour pressure of 260 torr. Is this an ideal solution? The vapour pressures of pure acetone and pure chloroform at 35oC are 345 and 293 torr, respectively.

(No, as expected vapour pressure is 319 torr compared with observed pressure of 260 torr)

2. A solution contains 3.5 mole of water and 1.5 mol of glucose (C6H12O6, non-volatile). What is the mole fraction of water in this solution? What is the vapour pressure of the solution at 25oC, given that the vapour pressure of pure water at 25oC is 23.8 torr?

(Mole fraction of water = 0.7, Vapour pressure = 17 torr)

3. Ethylene bromide, C2H4Br2, and 1,2-dibromopropane, C3H6Br2, form a series of ideal solutions over the entire range of composition. At 85°C the vapour pressures of these two pure liquids are 173 and 127 torr.

(a) If 10.0 g of ethylene bromide is dissolved in 80.0 g of 1,2-dibromopropane, calculate the partial pressure of each component and the total pressure of the solution at 85 °C.

(b) Calculate the mole fraction of ethylene bromide in the vapour in equilibrium with the above solution.

(c) What would be the mole fraction of ethylene bromide in a solution at 85 °c equilibrated with a 50:50 mole mixture in the vapour?

a) Ethylene bromide, 20.5 torr; 1,2-dibromopropane, 112 torr; total, 132 torr; (b) 0.155; (c) 0.42

4. (a) Calculate the vapor pressure of water above a solution prepared by adding 16.2 g of lactose, C12H22O11, to 105.7 g of water at 338 K, given the vapour pressure for pure water at 338 K is 187.5 torr and assuming lactose is non-volatile.

(b) Calculate the mass of propylene glycol, C3H8O2, that must be added to 0.500 kg of water to reduce the vapour pressure by 4.60 torr at 40°C, given the vapour pressure for pure water at 40oC is 55.3 torr and assuming propylene...