Discussion Forum

Calculate the depression in the freezing point of a solution  containing 0.1 g of $K_{3}[Fe(CN)_{6}]$ in 100 g of $H_{2}O$? (molecular  weight of  $K_{3}[Fe(CN)_{6}]$ =369; $K_{f}$=1.86 K Kg mol^-1)

Answer:

Explanation:

Given,

Mass of  $K_{3}[Fe(CN)_{6}]$ =0.1 g

 Mass of solvent =100 g

 Molar mass of $K_{3}[Fe(CN)_{6}]$ =329 g mol^-1 

$k_{f}$ =1.86 K kg/mol

$K_{3}[Fe(CN)_{6}]\rightleftharpoons3K^{+}+Fe(CN)_{6}]^{-}$

 i(van't Hoff factor)=3+1=4

 From, depression in freezing point,

$T_{f} =i \times K_{f} \times m$

 $T_{f}= 4 \times 1.86 K kg  /mol \times \frac{0.1 g}{329 g} \times  \frac{1000}{100 kg}$

 $T_{f}=0.0226 K$

Thus, option (c)  is correct