Colligative Properties

These are the properties that depend on the concentration of solute molecule or ions in solution but not on the chemical identity of the solute. 

For example, addition of ethylene glycol to water lowers the freezing point of water below 0°C. 

The magnitude of freezing point lowering is directly proportional to the number of solute molecules added to a particular quantity of solvent. 

(1) If 0.01 mole of ethylene glycol is added to 1 kg of water, the freezing point is lowered to - 0.019°C while

(2)  On adding 0.020 mole of ethylene glycol to 1 kg of water, the freezing point is lowered to -0.038°C. 

The various colligative properties are 

(1) Relative lowering of vapour pressure 

(2) Osmotic pressure 

(3) Elevation of boiling point 

(4) Depression of freezing point 

Henry's law constant for CO2​ in water is 1.67×10^8 Pa at 298K. Calculate the quantity of CO2​ in 500 ml of soda water when packed under 2.5 atm CO2​ pressure at 298K.

If N2 gas is bubbled through water at 293 K, how many millimoles of N2 gas would dissolve in 1 litre of water. Assume that N­2 exerts a partial pressure of 0.987 bar. Given that Henry’s law constant for N2 at 293 K is 76.84 kbar.

The solubility of gas is related to its mole fraction in the aqueous solution. The mole fraction of the gas in the solution is calculated by applying Henry’s law. Thus,

As 1litre water contains 55.5 mol of it, therefore, if n represents number of moles of N₂ in solution,

Related Questions:

(1) The vapour pressure of ethanol and methanol are 44.5 mm and 88.7 mm Hg respectively. An ideal solution is formed at the same temperature by mixing 60 g of ethanol with 40g of methanol. Calculate total vapour pressure of the solution.

(2) What is the composition of the vapour which is in equilibrium at 30°C with a benzene-toluene solution with a mole fraction of benzene of 0.400?