(b) Write the expression for the solubility-product constant for each of the following ionic compounds: MnCO₃, Hg(OH)₂, and Cu₃(PO₄)₃.

Verified step by step guidance

1. 1. The solubility product constant, Ksp, is the product of the concentrations of the ions, each raised to the power of its coefficient in the balanced chemical equation. It is used to describe the equilibrium between a solid and its ions in a solution.
2. 2. For MnCO3, the dissolution equation is: MnCO3(s) ⇌ Mn2+(aq) + CO3 2-(aq). So, the expression for the solubility product constant is: Ksp = [Mn2+][CO3 2-].
3. 3. For Hg(OH)2, the dissolution equation is: Hg(OH)2(s) ⇌ Hg2+(aq) + 2OH-(aq). So, the expression for the solubility product constant is: Ksp = [Hg2+][OH-]^2, because the coefficient of OH- is 2.
4. 4. For Cu3(PO4)2, the dissolution equation is: Cu3(PO4)2(s) ⇌ 3Cu2+(aq) + 2PO4 3-(aq). So, the expression for the solubility product constant is: Ksp = [Cu2+]^3[PO4 3-]^2, because the coefficients of Cu2+ and PO4 3- are 3 and 2, respectively.
5. 5. Remember, the solubility product constant, Ksp, does not include the concentration of the solid, as the activity of a pure solid is considered to be 1 in the equilibrium expression.

Key Concepts

Solubility Product Constant (Ksp)

The solubility product constant (Ksp) is an equilibrium constant that applies to the solubility of sparingly soluble ionic compounds. It is defined as the product of the molar concentrations of the ions, each raised to the power of their coefficients in the balanced dissolution equation. Ksp provides insight into the extent to which a compound can dissolve in water, with higher values indicating greater solubility.

Dissociation of Ionic Compounds

Ionic compounds dissociate into their constituent ions when they dissolve in water. For example, when MnCO3 dissolves, it separates into Mn²⁺ and CO3²⁻ ions. Understanding the dissociation process is crucial for writing the Ksp expression, as it determines the ions involved and their respective stoichiometric coefficients in the equilibrium expression.

Writing Ksp Expressions

To write the Ksp expression for an ionic compound, one must first identify the ions produced upon dissolution and their stoichiometric ratios. The Ksp expression is formulated by multiplying the concentrations of the ions, each raised to the power of their coefficients from the balanced equation. This process is essential for calculating the solubility of the compound and understanding its behavior in solution.