Question

How do you calculate freezing point depression?

Answer 1

Hint : This question is one of the most important questions from the chapter solutions. The topic is also one of the most important topics in the chapter. It is also very important from a competition point of view. To solve this question you just need to know some basics of this topic especially about temperature difference and van’t Hoff factor. The complete detailed solution is given in the below section.

Complete Step By Step Answer:
If you have studied the chapter solutions, then you should know that there is a topic in this chapter which is known as colligative properties. This depression in freezing point is also one of the colligative properties of matter. It depends upon the number of particles and not on the chemical identity of the particles and also on their mass. Now freezing point depression is calculated by using Raoult’s law and Clausius-Clapeyron equation to write an equation which is known as Blagden’s law. In the ideal solution, the freezing point depression only depends upon the concentration of the solute. For example: Calculate depression in freezing point for $0.56$ molal aqueous solution of $KCl$ . (Given: $K_{f\left(H_{2}O\right)}=1.8K\text{ Kgmo}{\text{l}}^{-1}$ ).
 $\mathrm{\Delta }{T}_f=i\times K_f\times m$
 $=2\times 1.8\times 0.56$ $=2.016$

Note :
The actual meaning of the freezing point depression is that it is a drop in the temperature at which a substance freezes and it happens when a smaller amount of another, non-volatile substance is added. Some of the examples to illustrate the above statement are adding salt into water, alcohol in water, and the mixing of two solids such as impurities into a finely powdered drug.