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. $
