a. Thallium(I) chloride is a salt that is sparingly soluble in water. When hydrochloric acid is added to a saturated solution of thallium(I) chloride, a precipitate is formed. Explain why a precipitate is formed.

b. Calcium sulfate is a sparingly soluble salt that can be made by mixing solutions containing calcium and sulfate ions. A 0.001 00 mol dm^–3 solution of aqueous calcium chloride, CaCl₂, is mixed with an equal volume of 0.001 00 mol dm^–3 solution of aqueous sodium sulfate, Na₂SO₄.

i. Calculate the concentration of calcium and sulfate ions when equal volumes of these solutions of calcium chloride and sodium sulfate are mixed.

ii. Will a precipitate of calcium sulfate form? (Ksp of calcium sulfate = 2.0 × 10^–5 mol² dm^–6)