Equation for dissolving calcium carbonate in water:
CaCO3(s) ⇄ Ca²⁺(aq) + CO₃²⁻(aq).
The equilibrium constant expression for this reaction: K = [Ca²⁺] [CO₃²⁻] / [CaCO3(s)], but concentration of CaCO3(s) is 1 (for all solid), so
the simpler expression for the equilibrium constant is:K = [Ca²⁺] [CO₃²⁻].
