Question

The depression in freezing point for $0.01 \,m$ aqueous solution of $K_{x}\left[F e(C N)_{6}\right]$ is $0.0744 \,K$. The molal depression constant for solvent is $1.86 \,K \,kg\, mol ^{-1}$. If the solute undergoes complete dissociation, what is the correct molecular formula for the solute?

• A. $K_{2}\left[F e(C N)_{6}\right]$
• B. $K_{3}\left[F e(C N)_{6}\right]$
• C. $K\left[ Fe ( CN )_{6}\right]$
• D. $K_{4}\left[F e(C N)_{6}\right]$

Answer 1

Answer: (B)

$\Delta T_{b}=i K_{ f } m$
$0.0744= i \times 1.86 \times 0.01$
$\Rightarrow i =4$
So, $n =4$
Formula is $K_{3}\left[ Fe ( CN )_{6}\right]$