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Give reasons for the following : When mercuric iodide is added to an aqueous solution of KI, the freezing point is raised.

Give reasons for the following :
When mercuric iodide is added to an aqueous solution of KI, the freezing point is raised.

Grade:11

1 Answers

Sunil Kumar FP
askIITians Faculty 183 Points
8 years ago
The virtually insoluble HgI2 complexes with the I- (from the KI) to give the soluble [HgI4]^2- ion:
Hg2+ + 4 I- ⇄ [HgI4]2- Kform = 1.9 x 10^30
The net result is
2I-(aq) + HgI2(s) → [HgI4]2-(aq)
As can be seen, this complexation reaction reduces the number of particles in solution from 4n (includes 2n K+(aq) ions) to 3n (n = original number of moles of KI) and consequently the freezing point is raised

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