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(b) When mercuric iodide is added to an aqueous solution of KI, the freezing point is raised.

(b) 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
9 years ago
In the presence iodide, Hg(II) forms a very stable HgI₄²⁻ complex:

Hg²⁺ + 4 I⁻ ⇌ HgI₄²⁻ . . . Kf = 6.8 × 10²⁹

Suppose, for example, you had one liter of a 0.1 M solution of KI, you'd have [K⁺] = 0.1 M and [I⁻] = 0.1 M. Now if you add 0.05 mol HgI₂ you have [K⁺] = 0.1 M and [HgI₄²⁻] = 0.05 M. The total ionic concentration is reduced the freezing point depression (compared to pure water) is reduced too. Therefore, the freezing point (compared to te KI solution) is raised.

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