Colligative Properties
Colligative Properties
1. Boiling Point Elevation – The increase in boiling point of a solution relative to that of the pure solvent is directly proportional to the number of solute particles per mole of solvent molecules. That is,
DTb = i Kb m
where DTb = increase in boiling point relative to that of the pure solvent, Kb is called the molal boiling point elevation constant, and m = molality of the solution.
2. Freezing Point Depression – Like the boiling point elevation, the decrease in freezing point of a solution relative to that of the pure solvent is directly proportional to the molality of the solute. That is, DTf = iKf m
where DTf = decrease in freezing point relative to that of the pure solvent, Kf is called the molal freezing point depression constant, and m = molality of the solution.
Workshop on Colligative Properties
1. Determine the vapor pressure of a solution of 92.1 g of glycerin, C3H5(OH)3, in 184.4 g of ethanol at 40 °C. The vapor pressure of pure ethanol is 0.178 atm at 40 °C, and glycerin is essentially nonvolatile.
2. Find the boiling point of a solution of 92.1 g of iodine in 800.0 g of chloroform.
3. Calculate the freezing point of a solution of 0.724 g of calcium chloride in 175 g of water, assuming complete dissociation by the solute.
4. Determine the osmotic pressure of a solution with a volume of 0.750 L that contains 5.0 g of methanol in water at 37 °C.
5. List the following aqueous solutions in order of their expected freezing points: 0.050 m CaCl2, 0.15 m NaCl, 0.10 m HCl, 0.050 m HC2H3O2, and 0.10 m C12H22O11.
