Equilibrium Question 300

Question: The values of $ K _{sp} $ for $ CuS,Ag_2S $ and $ HgS $ are $ {10^{-31}},,10^{42} $ and $ {10^{-54}} $ respectively. The correct order of their solubility in water is [MP PMT 2003]

Options:

A) $ Ag_2S>HgS>CuS $

B) $ HgS>CuS>Ag_2S $

C) $ HgS>Ag_2S>CuS $

D) $ Ag_2S>CuS>HgS $

Show Answer

Answer:

Correct Answer: D

Solution:

$ Ag_2S>CuS>HgS $ . Solubility of CuS $ =\sqrt{{10^{-31}}}=3.16\times {10^{-16}}mol/lit. $ Solubility of $ Ag_2S $

$ =\sqrt[3]{\frac{K _{sp}}{4}}=\sqrt[3]{\frac{{10^{-42}}}{4}}=6.3\times {10^{-5}}mole/litre $ Solubility of HgS $ =\sqrt{K _{sp}}=\sqrt{{10^{-54}}} $

$ ={10^{-27}}mol/litre. $



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