Question

determine the colligitive molarity of a truly saturated salt solution and it's freezing point

Answer 1

We know that, the freezing point depression of a solution is given as:

Tf = Kf * i * m    ...................(1)

where,

Tf = depression in freezing point

Kf = molal freezing point depression constant

i = van 't Hoff factor

m = molality of solution

Now,

Let w be the mass of solute (molecular weight is M.W) in W grams of solvent and V is the volume of the solution.

m = Moles of solute / Mass of solvent (kg)

m = w * 1000 / ((M.W) * W)

W = w * 1000 / ((M.W) * m)

and,

Molarity, M = w * 1000 / ((M.W) * V)

V = w * 1000 / ((M.W) * M)

density, d = (w + W) / V

Solving this we get;

Putting above value of m in equation (1).

Freezing point of solution = T^of - Tf

where, T^of is its freezing point in its pure state