Question

What is the equilibrium expression for: Ca(OH)₂(s) ⟺ Ca²⁺(aq) + 2OH⁻(aq)?

Select one:
a. Kₑᵩ = [Ca²⁺]
b. Kₑᵩ =[OH⁻]
c. Kₑᵩ =[OH⁻]²
d. Kₑᵩ =[Ca²⁺][OH⁻]
e. Kₑᵩ =[Ca²⁺][OH⁻]²
f. Kₑᵩ =[Ca²⁺][OH⁻]/[Ca(OH)₂]
g. [Ca²⁺][OH⁻]²/[Ca(OH)₂]

Answer 1

The equilibrium expression for the dissolution of Ca(OH)₂ into its ions is Ksp = [Ca²⁺][OH⁻]², which reflects the stoichiometry of the reaction and the full dissociation of the strong base in solution.

Step-by-step explanation:

The equilibrium expression for the dissolution of Ca(OH)₂ into Ca²⁺ (aq) and OH⁻ (aq) ions is based on the solubility product constant (Ksp). Because Ca(OH)₂ is a strong base and fully dissociates in solution, the solid does not appear in the expression. The correct equilibrium expression would be the one representing the concentrations of the products raised to the power of their stoichiometric coefficients in the balanced equation. Therefore, the expression is Ksp = [Ca²⁺][OH⁻]2. This takes into account that there are two moles of OH⁻ for every mole of Ca²⁺ produced.

The equilibrium expression for the given reaction is:

Ke = [Ca2+][OH-]2

The equilibrium expression is obtained by multiplying the concentration of the products (Ca2+ and OH-) raised to their stoichiometric coefficients (1 and 2 respectively). The reactant, Ca(OH)2, is not included in the expression as it is a solid and its concentration is considered constant.