JEE Main · 2018 · 08 Apr 2018 · Offline · Solutions

For 1 molal aqueous solution of the following compounds, which one will show the highest freezing point ?

(A) $[Co (H_{2} O)_{3} Cl_{3}] \cdot 3 H_{2} O$ ✓ Correct
(B) $[Co (H_{2} O)_{6}] Cl_{3}$
(C) $[Co (H_{2} O)_{5} Cl] Cl_{2} \cdot H_{2} O$
(D) $[Co (H_{2} O)_{4} Cl_{2}] Cl \cdot 2 H_{2} O$

Answer: (A)

Solution

Freezing-point depression depends only on the number of dissolved particles, so the complex that releases the fewest ions depresses the freezing point least and freezes highest. The isomer with all three chlorides bound inside the coordination sphere does not ionise at all, giving a van't Hoff factor of

1

, while the others give

2

3

4

ions. With the smallest particle count, that non-ionising complex shows the highest freezing point.

JEE Main · 2018 · 08 Apr 2018 · Offline · Single correct option

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