Question

Discuss why the freezing point of a solution is typically lower than the freezing point of pure solvent?

why molality is used as the unit of concentration in colligative property calculation?

Answer 1

Solution :-

The freezing point is the state where the liquid phase and solid phase are in equilibrium with each other

When we add solute to the liuid then the potential of the liquid phase decreases therefore it becomes more stable than solid phase

The concentration of the solute is directly proportional to the freezing point decrease of the solution. Therefore the freezing point of the solution is lower than the freezing point of the pure solvent.

In the calculation of the concetration of the colligative property calculations the molaity is the unit used for the concentration because. Molaity is moles per kg solvent the mass of the solvent does not change so the concentration also does not chages for the solution if the molarity is used then as the temperature changes the volume of the liquid can change because volume is affected by the temperature so the concetration also chages which would lead to the incorrect calculations therefore in the colligative property calculations concentration is used in molality.