CAIE IGCSE Chemistry – Salts & Indicators quick notes: solubility rules (nitrates, chlorides, sulfates; Na/K/NH₄ carbonates & hydroxides), indicator colours (methyl orange, litmus, universal, phenolphthalein, thymolphthalein).  Includes pH scale and key transition-metal colours (CuSO₄ blue, CuO black, CuCO₃ green, MnO₂ black, Fe²⁺ pale green, Fe³⁺ brown/orange) for fast revision.