Question

In: Chemistry

Which of the following compounds becomes more soluble as pH decreases? Ca(NO3)2(s) PbBr2(s) AgCl(s) Ca(OH)2(s)

Which of the following compounds becomes more soluble as pH decreases?

	Ca(NO₃)₂(s)
	PbBr₂(s)

	AgCl(s)
	Ca(OH)₂(s)

Expert Solution

The pH does not affect the solubility of compounds that are formed by anions that are conjugate base of strong acids. This happens because these anions are not protonated by the H⁺ ion. This happen in the following examples,

Dissociation reaction of Ca(NO₃)₂

Ca(NO₃)₂ --> Ca⁺² + 2 NO₃^-

The anion NO₃^- is the conjugate base of the strong acid HNO₃. So that, the pH does not affect its solubility.

Dissociation reaction of PbBr₂

PbBr₂ -->Pb⁺² + 2 Br^-

The anion Br^- is the conjugate base of the strong acid HBr. So that, the pH does not affect its solubility.

Dissociation reaction of AgCl

AgCl -->Ag⁺ + Cl^-

The anion Cl^- is the conjugate base of the strong acid HCl. So that, the pH does not affect its solubility.

But in the case of Ca(OH)₂, this is dissociated in the following way,

Ca(OH)₂ --> Ca⁺² + 2OH^- (1)

If the pH decreases by the addition of some acid, the HO^- ions reacts with the H⁺ of the acid added in the following way,

H⁺ + HO^- à H₂O (2)

The reaction 2 produces that the concentration of HO^- decreases, so that, the equilibrium of reaction 1 is lost. According to the precipice of Le Châtelie, the reaction 1 t will move to the right ( to the products). In this way the concentration of HO^- will increase and the concentration of Ca(OH)₂ will decrease allowing to reestablish the equilibrium. This decrease in the concentration of Ca(OH)₂ shows one increase in its solubility. So that, the solubility of Ca(OH)₂ increases when the pH decreases.

queen_honey_blossom answered 2 years ago

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