Question

In which aqueous solution will the most CaSO4 dissolve?

1)0.1 M CaCl2

2)0.1 M ZnSO4

3)0.1 M (NH4)2S

4)0.1 M Na2SO4

Answer 1

3) 0.1 M (NH₄)₂S

in the ammonium sulfide solution

Answer 2

In 0.1 M
`(NH_(4))_(2)S` solution,
`CaSO_(4)` will be most soluble

Step-by-step explanation:

Dissociation equilibrium of
`CaSO_(4)` :

`CaSO_(4)\rightleftharpoons Ca^(2+)+SO_(4)^(2-)`

According to Le-chatliers principle, addition of either
`Ca^(2+)` or
`SO_(4)^(2-)` ions into solution of
`CaSO_(4)` leads to shifting in dissociation equilibrium toward left. Therefore solubility of
`CaSO_(4)` decreases.

According to Le-chatliers principle, removal of either
`Ca^(2+)` or
`SO_(4)^(2-)` ions into solution of
`CaSO_(4)` leads to shifting in dissociation equilibrium toward right. Therefore solubility of
`CaSO_(4)` increases.

`Ca^(2+)` gets removed from solution by forming sparingly soluble salt CaS upon addition of
`(NH_(4))_(2)S` solution.

So solubility of
`CaSO_(4)` increases upon addition of
`(NH_(4))_(2)S` solution