CaO (quicklime): Made by heating CaCO3 in lime kiln. Reacts with water exothermically: CaO + H2O → Ca(OH)2 (slaking). Ca(OH)2 (slaked lime): Used in whitewashing, water treatment, sugar refining. Ca(OH)2 + CO2 → CaCO3 (milky) + H2O; CaCO3 + CO2 + H2O → Ca(HCO3)2 (milkiness disappears). CaSO4.2H2O (gypsum): Heated at 120 degrees C → CaSO4.1/2H2O (Plaster of Paris, POP). POP sets by rehydration: CaSO4.1/2H2O + 3/2 H2O → CaSO4.2H2O (expands slightly — good for moulds). Heated above 200 degrees C → anhydrous CaSO4 (dead burnt plite, does not set). MgSO4.7H2O (Epsom salt): Purgative. BaSO4: Insoluble, used as barium meal for X-ray of GI tract (opaque to X-rays but non-toxic because insoluble).