Question

Write the ionic equation for dissolution and the solubility product (K_sp) expression for each of the following slightly soluble ionic compounds. (For the ionic equations, include states-of-matter under the given conditions in your answer.

Solubility equilibrium expressions take the general form: K_sp = [Aⁿ⁺ ]^a . [B^m− ]^b. Subscripts and superscripts that include letters must be enclosed in braces {}. For example: K_sp=[A⁺]².[B^2-] must be typed using K_{sp}=[A^+]^2.[B^2-]

(a) Cu₃(PO₄)₂

Net ionic equation

Solubility product expression

(b) Ag₂S

Net ionic equation

Solubility product expression

(c) BaSO₃

Net ionic equation

Solubility product expression

(d) BaF₂

Net ionic equation

Solubility product expression

AND

Use solubility products and predict which of the following salts is the most soluble, in terms of moles per liter, in pure water. (Hint: The size of Ksp tells us about solubility in general, but technically you must calculate the molar solubility in order to compare.)

Special note: mercury(I) ions forms a dimer and behaves like a polyatomic ion. So, Hg₂X₂ breaks into Hg₂²⁺ + 2X^-

Hg₂I₂, Ksp= 5.2e-29
Sn(OH)₂, Ksp= 5.5e-27
Ag₂SO₄, Ksp= 1.2e-05
BaF₂, Ksp= 1.8e-07

Answer 1

To write the net ionic equation we need to consider the following:

• The products of the dissociation equation will be the ions that make up the compound.
• It is important to include the right coefficient and the right ion charge. The coefficient equals the amount of ions in the compound, for example a compound with a formula AB has 1 A⁺ ion and 1 B^- ion (considering that the charges of the ions are +1 and -1, like Na⁺ and Cl^-).

To write the solubility product (ksp) expression, we use the coefficients of the net ionic equation as superscripts in the concentration of the ion. For example:

A₂B₃ <=> 2A³⁺ + 3B^2-

ksp = [A³⁺]²[B^2-]³

With that in mind we can answer the problem:

(a) Cu₃(PO₄)₂

Net ionic equation: Cu₃(PO₄)₂ (s) <=> 3Cu²⁺ + 2PO₄^3-

Solubility product expression: ksp = [Cu²⁺]³[PO₄^3-]²

(b) Ag₂S

Net ionic equation: Ag₂S (s) <=> 2Ag⁺ + S^2-

Solubility product expression: ksp = [Ag⁺]²[S^2-]

(c) BaSO₃

Net ionic equation: BaSO₃ <=> Ba²⁺ + SO₃^2-

Solubility product expression: ksp = [Ba²⁺][SO₃^2-]

(d) BaF₂

Net ionic equation: BaF₂ <=> Ba²⁺ + 2F^-

Solubility product expression: [Ba²⁺][F^-]²