Question

Pure water as well as separate equimolal and dilute aqueous solutions of $NaCl,K_3\left[Fe(CN{)}_6\right]$ and $K_4\left[Fe(CN{)}_6\right]$ represented respectively as $I$ II, III and IV are available. Which of the following statements is correct, assuming $100\%$ dissociation of all solutes?

• A. I < II < III < IV is the increasing order of freezing points
• B. IV < III < II < I is the increasing order of freezing points
• C. IV < III < II < I is the increasing order of boiling points
• D. IV < III < II < I is the increasing order of van't Hoff factors

Answer 1

Answer: (B)

$\Delta T_f=i\times K_f\times m.i$ values of $NaCl,K_3\left[Fe(CN{)}_6\right]$ and $K_4\left[Fe(CN{)}_6\right]$ are respectively $2,4$ and $5$.
Hence, $K_4\left[Fe(CN{)}_6\right]$ shows the largest depression and the lowest freezing point.
Water has the highest freezing point of $0^{\circ }C$.
Also $\Delta T_b=i\times$ molality.
IV has the highest $\Delta T_b$ and the highest boiling point.
The increasing order of boiling points is $I<II<III<IV$