Question

A 0.001 molal solution of a complex $\left[M{A}_8\right]$ in water has the freezing point of $-{0.0054}^{\circ }C$. Assuming 100% ionization of the complex salt and $K_f$ for $H_{2}O=1.86k.m^{-1}$, write the correct representation for the complex.

• A. $\left[M{A}_8\right]$
• B. $\left[M{A}_7\right]A$
• C. $\left[M{A}_6\right]A_2$
• D. $\left[M{A}_5\right]A_3$

Answer 1

The correct option is C $\left[M{A}_6\right]A_2$

The expression for the depression in freezing point is $\Delta T_f=k_f\times m\times i$

Substitute values in the above expression

$0.0054=1.86\times 0.001\times i$

$i=2.9\simeq 3$

Thus one molecule of the complex on dissociation gives 3 particles.

Hence, the complex can be represented as $\left[M{A}_6\right]A_2$

Hence, the correct option is $C$