Question

The depression in freezing point for $0.01m$ aqueous solution of $K_x\left[Fe{\left(CN\right)}_6\right]$ is $0.0744K$. The motal depression constant for solvent is $1.86K$ $kg$ ${mol}^{-1}$. If the solute undergoes complete dissociation, what is the correct molecular formula for the solute?

• A. $K_2\left[Fe{\left(CN\right)}_6\right]$
• B. $K_3\left[Fe{\left(CN\right)}_6\right]$
• C. $K^{}\left[Fe{\left(CN\right)}_6\right]$
• D. $K_4\left[Fe{\left(CN\right)}_6\right]$

Answer 1

The correct option is B $K_3\left[Fe{\left(CN\right)}_6\right]$

$\Delta T_b=i{K}_{f}m$
$0.0744=i\times 1.86\times 0.01$
$i=4$
So, $n=4$
Formula is $K_3\left[Fe{\left(CN\right)}_6\right]$