Question

The freezing point (in ${ }^{\circ} C$ ) of a solution containing $0.1\, g$ of $K _{3}\left[ Fe ( CN )_{6}\right.$ (Mol. Wt. 329$)$ in $100\, g$ of water $\left( K _{ f }=1.86\, K\, kg\, mol ^{-1}\right)$ is

• A. $-2.3 \times 10^{-2}$
• B. $-5.7 \times 10^{-2}$
• C. $-5.7 \times 10^{-3}$
• D. $-1.2 \times 10^{-2}$

Answer 1

Answer: (A)

$K _{3}\left[ Fe ( CN )_{6}\right] \rightarrow 3 K ^{+}+\left[ Fe ( CN )_{6}\right]^{3-}$
$i =4$
$\Delta T _{ f }= K _{ f } \times i \times \frac{ m }{ M } \times \frac{1000}{ W }$
$=1.86 \times 4 \times \frac{0.1}{329} \times \frac{1000}{100}$
$=2.3 \times 10^{-2}$
$T _{ f }=-2.3 \times 10^{-2}$