Ion-exchange reactions

In electrolyte solutions reactions go on between ions, and a reaction goes to completion only if at least one product is an insoluble precipitate, a gas or a weak electrolyte (such as water). We write the equation in three forms: molecular; full ionic (strong electrolytes as ions, precipitates, gases and weak electrolytes as molecules); and net ionic (identical ions on both sides are cancelled). The essence of neutralisation is H⁺ + OH⁻ → H₂O, so HCl + KOH and HNO₃ + NaOH have the same net ionic equation. Ba²⁺ + SO₄²⁻ → BaSO₄↓ detects the sulfate ion, Ag⁺ + Cl⁻ → AgCl↓ the chloride ion and Cu²⁺ + 2OH⁻ → Cu(OH)₂↓ the copper(II) ion; CO₃²⁻ gives CO₂ gas with an acid, and Na⁺ colours a flame yellow and K⁺ violet. If all ions stay free in solution (e.g. KCl with NaNO₃) there is no reaction. Experiments, especially with acids and alkalis, are shown or supervised by the teacher only.