Question

The freezing point (in ${}^{\circ }$ C) of solution containing 0.1g of $K_3\left[Fe\right(CN{)}_6]$ (mol.wt. 329) in 100g of water ($K_f=1.86Kkgmo{l}^{-1}$) 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

The correct option is A

$-2.3\times {10}^{-2}$

Van't hoff factor (i) $=4\{3K^{+}+{\left[Fe\right(CN{)}_6]}^{3-}\}$
$=\frac{0.1}{329}\times \frac{1000}{100}=\frac{1}{329}$
$\Rightarrow \Delta T_f=i{K}_f.m=4\times 1.86\times \frac{1}{329}=2.3\times {10}^{-2}$
$\Rightarrow T-f=-2.3\times {10}^{-2}{}^{\circ }C$