Question

Which will have the lowest freezing point?
A) A 0.01 molar solution of $HN{O_3}$
B) A 0.01 molar solution of $H{C_2}{H_3}{O_2}$
C) A 0.01 molar solution of $Cu{\left( {N{O_3}} \right)_2}$
D) A 0.01 molar solution of $NaN{O_3}$

Answer 1

Freezing point of the solvent in a solution changes because the concentration of the solute in the solution changes. But it does not depend on the identity of either the solvent or the solute particles. We have to count the amount of dissociation of the ions of each solute. The greater the dissociation, the lower will be the freezing point.

Complete step by step answer:
- The freezing point is defined as the temperature at which a liquid becomes a solid or freezes. Usually, increased pressure raises the freezing point like it happens with a melting point (though slightly). But the opposite also happens. If we add a volatile or non-volatile solute (which is insoluble to a solid solvent) to a definite solvent, we can see the opposite effect on the freezing point of the solution. The solution will have a lower freezing point than in the case of the pure solvent.
- Again, the freezing point also depends on the number of ions dissociated or on the concentrations of the particles when the compounds will dissociate in their aqueous solution. The greater the dissociation, the lower will be the freezing point.
- Similarly, the 0.01-molar solution of $Cu{\left( {N{O_3}} \right)_2}$ will have the lowest freezing point. Because of the dissociation of one molecule of cupric nitrate, it gives 3 ions. But all other solutes in the solution will give less ion. As the cupric nitrate gives the maximum number of particles in solution, the depression in freezing point for cupric nitrate is maximum.

The correct option is (A).

Note: We should remember that the depression in freezing point is a colligative property. The colligative property explains the property of the solution, which depends on the ratio of the number of solute particles to the solvent molecules. Also, does not depend on the nature of the chemicals present.