7.12 Common-Ion Effect

Adding an ion already in the equilibrium (like Cl⁻ to AgCl) shifts the equilibrium left, so less solid dissolves.

Solve with the common ion's concentration in the ICE table.

AgCl in 0.10 M NaCl: Ksp = s(0.10) → s = 1.8 × 10^−9 M (vs. 1.3 × 10^−5 in water).

Worked example: Why does CaF₂ dissolve less in NaF solution? Extra F⁻ pushes the equilibrium toward solid.