Ionic EquilibriumHard

Question

On dissolving a substance in water, it can produce either an ionic or molecular solution. From the following data, predict what type of solution is likely to be formed by CaCl2 and HgCl2 at 25°C?

The maximum contribution of T∆S in dissolution process is 30 kJ at 25°C

Options

A.both ionic.
B.both molecular.
C.CaCl2 is ionic but HgCl2 is molecular.
D.CaCl2 is molecular but HgCl2 is ionic.

Solution

For molecular solubility of CaCl2,

ΔHsolution = 209.2 + (–33.5) = 175.7 KJ > 30 KJ

For ionic solubility of CaCl2,

ΔHsolution = 209.2 + 1004.2 + 1715.4 – 1598.3 – 719.6 – 711.2 = – 100.3 KJ

For molecular solubility of HgCl2,

ΔHsolution = 83.7 – 66.9 = 16.8 KJ < 30 KJ

For ionic solubility of HgCl2,

ΔHsolution = 83.7 + 460.2 + 2815.8 – 1845.1 – 719.6 – 711.2 = 83.3 KJ > 30 KJ

Hence, CaCl2 is ionic and HgCl2 is molecular solubility.

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