Question

Describe in general terms an experiment to determine the molal freezing point depression constant of water. assume the availablity of deionized water and solid NaNO3

Answer 1

The phenomenon of freezing of a solution at a temperature lower than the pure solvent is called freezing point depression. This is a colligative property of the solution and depends upon the number of dissolved particles in the solution. Thus a higher solute concentration results in greater freezing point depression

The freezing point depression of any electrolytic solution can be calculated by using the equation,

Tf = i Kf m

Where Kf is the molal freezing point depression constant of the solvent

m is the molality

i is the Van’t Hoff Factor

The experimental procedure for the determination of freezing point depression is as follows

1. Place 10 mL of deionized water in a test tube. Insert a stirring apparatus and immerse a thermometer in the liquid.

2. Place the entire experimental setup in a salt ice-bath. Allow the water to cool with stirring until ice-water slush is formed.

3. Remove the test tube and note temperature. This is the freezing point of pure water.

4. In a similar manner, find the freezing point of 1.00 g of NaNO₃ in 10.0 g of water

Now, freezing point depression can be calculated as,

Freezing point depression:, Tf = Tf^o - Tf

Where Tf^o is the freezing point of pure solvent

Tf is the freezing point of solution