Question

Which one of the following solutions has the lowest freezing point ?

• A. 0.1 M Urea
• B. 0.1 M $BaC{l}_2$
• C. 0.2 M $NaN{O}_3$
• D. 0.2 M $N{a}_{2}S{O}_4$

Answer 1

The correct option is D 0.2 M $N{a}_{2}S{O}_4$

$\Delta T_f$ is directly proportional to the number of the particles of solute.

Here among all given solute, the particles of 0.2 M $N{a}_{2}S{O}_4$ are highest in number.

As 0.2 mol of $N{a}_{2}S{O}_4$ dissociates to give 0.4 mol of $N{a}^{+}$ and 0.2 mol of $S{O}_4^{2-}$

Hence total moles in 1 L of solution of $N{a}_{2}S{O}_4$ is 0.6 moles. ( after dissociation)

Whereas others have lesser moles of ions in solutions.

Hence the 0.2 M $N{a}_{2}S{O}_4$ has the lowest freezing point due to the highest moles of ions in solution.