Question

Which of the following compounds solubility will not be affected by a low pH in solution?

Group of answer choices

SrF2

AgCl

CaCO3

CuS

Ca(OH)2

Answer 1

Answer : AgCl

The solubility of AgCl is unaffected by changes in pH because Cl– is the anion of a strong acid (HCl) and therefore has negligible basicity.

Other compounds:

Decreasing the pH increases the solubility of sparingly soluble bases and basic salts. This is governed by the Le- Chateliers principle.

CaCO3 is the sparingly soluble salt of the strong base Ca(OH)2 and the weak acid H2CO3.

CaCO3(s)⇌Ca2+(aq)+CO2-3(aq)

CO2-3 is a base.

CO2-3(aq)+H2O(l)⇌HCO3-(aq)+OH-(aq)

The overall equilibrium is

CaCO3(s)+H2O(l)⇌Ca2+(aq)+HCO3-(aq)+OH-(aq)

If we decrease the pH by adding H3O+ ions, the added H3O+ ions will react with the OH- ions and form water.

Then according to the principle the equilibrium will move to the right and the solubility will increase.

the solubility of CaF2 increases as the solution becomes more acidic, because the F– ion is a weak base; it is the conjugate base of the weak acid HF. As a result, the solubility equilibrium of CaF2 is shifted to the right as the concentration of F– ions is reduced by protonation to form HF.

Cafz(s) – Ca2+ (aq) + 2F (aq)

F (aq) + H+ (aq) – HF(aq)

The equation for the overall process is

CaF(s) + 2H+ (aq) Ca?+ (aq) + 2HF(aq)

Similar scenerio will be for SrF2 and CuS .

***Salts that contain basic anions, such as CO32–, PO43–, CN–, or S2–, behave similarly.

The solubility of Ca(OH)2 greatly increases as the acidity of the solution increases as the alkali and alkaline earth metal hydroxides contains strongly basic OH

ion.