Question

9. Calculate the freezing point and boiling point of the following aqueous solutions, assuming
complete dissociation:
(a) 10.5 g FeCl3 in 1.50

Answer 1

(a) The expression for the depression in the freezing point is

Here, Kf is the depression in the freezing point constant, W2 is the mass of solute in kg, M2 is the molar mass of solute in kg and W1 is the mass of water in kg.

Substitute values in the above expression.

The freezing point of the solution is

The expression for the elevation in boiling point is

Here, Kb is the elevation in boiling point constant, W2 is the mass of solute in kg, M2 is the molar mass of solute in kg and W1 is the mass of water in kg.

Substitute values in the above expression.

The boiling point of the solution is

(b) The expression for the depression in the freezing point is

Here, Kf is the depression in the freezing point constant, W2 is the mass of solute in kg, M2 is the molar mass of solute in kg and W1 is the mass of water in kg.

Substitute values in the above expression.

The freezing point of the solution is

The expression for the elevation in boiling point is

Here, Kb is the elevation in boiling point constant, W2 is the mass of solute in kg, M2 is the molar mass of solute in kg and W1 is the mass of water in kg.

Substitute values in the above expression.

The boiling point of the solution is

(c) The expression for the depression in the freezing point is

Here, Kf is the depression in the freezing point constant, and m is the molality of the solution.

Substitute values in the above expression.

The freezing point of the solution is

The expression for the elevation in boiling point is

Here, Kb is the elevation in boiling point constant and m is the molality of the solution.

Substitute values in the above expression.

The boiling point of the solution is