Excess solid CaSO₄ is added to pure water atpH7,with undissolved solid remaining. Ksp=2.1×10⁻⁵ mol²/L². Find equilibrium sulfate concentration in mol/L, to three decimals.
Dissolution $CaSO_4\rightleftharpoons Ca^{2+}+SO_4^{2-}$ gives equal ion concentrations s in the ideal pure-water model. Ksp=s²,so s=√(2.1×10⁻⁵)=.00458258 M. Rounded, sulfate is **.005 mol/L**. Excess solid ensures saturation;it does not imply all added solid dissolves.
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