What does Ksp stand for?

• A. The solubility product; the product of ion concentrations at saturation.
• B. The sum of ion concentrations at saturation.
• C. The rate constant for precipitation.
• D. The equilibrium constant for gas dissolution.

Answer: (A)

Ksp is the solubility product constant for a sparingly soluble salt, representing the equilibrium condition when the solid is present and the solution is saturated. For a dissolution like MX(s) ⇌ M+(aq) + X−(aq), Ksp = [M+][X−]. More generally, for a salt with stoichiometry aA^(n+) + bB^(m−) ⇌ ... the Ksp is the product of the ion concentrations raised to their coefficients, evaluated at saturation. This product is constant at a given temperature, reflecting the balance between dissolution and precipitation. The concept here is that the dissolved ion concentrations settle to fixed values that satisfy this product, regardless of how much solid remains or is consumed, as long as the system is at equilibrium.

So the statement that Ksp is the product of ion concentrations at saturation captures the essence: it’s the equilibrium constant for the dissolution process, not a simple sum of concentrations, not a rate constant for precipitation, and not a constant for gas dissolution.