Question

Which one of the following aqueous solutions will have the lowest freezing point ?

• A. $0.1$ molal solution of urea
• B. $0.1$ molal solution of sucrose
• C. $0.1$ molal solution of sodium chloride
• D. $0.1$ molal solution of calcium chloride

Answer 1

Answer: (D)

$0.1$ molal solution of calcium chloride

Depression in freezing point is a colligative property which depends upon the amount of the solute.

$\Delta T_f=i\times k_f\times m$

where $T_f$ is the change in freezing point, $i$ is Vant Hoff factor, $m$ is molality and $k$ is freezing point constant.

1% glucose will have Vant Hoff factor 1, 1% sucrose will have Vant Hoff factor 1.

Also, 1% NaCl will have Van't Hoff factor 2 and 1 % $CaC{l}_2$ will have Vant Hoff factor $i$ as 3.

Thus 1% $CaC{l}_2$ produces most ions and thus lowers the freezing point to the maximum value.

The correct option is $D$.