Question

The freezing point depression constant for water is $-1.86^{\circ} Cm^{-1}$. If $5.00 \,g$ $Na_2SO_4$ is dissolved in $45.0\,g$ $H_2O$, the freezing point is changed by $- 3.82^{\circ} C$. Calculate the Van't Hoff factor for $Na_2SO_4$.

• A. 0.381
• B. 2.05
• C. 2.63
• D. 3.11

Answer 1

Answer: (C)

Using, $\Delta T _{ f }= i \times K _{ f } {\times m }$

$i =\frac{\Delta T _{ f } \times W _{ A }}{ K _{ f } \times n _{ B } \times 1000}$

$=\frac{3.82 \times 45}{1.86 \times\left(\frac{5}{142}\right) \times 1000} $

$=2.63$