The rest of the anions and a decision chart

The second group uses concentrated sulphuric acid, which is more stable and less volatile than the acids of the anions, so it displaces them from the solid salt as gases: 2NaCl + H₂SO₄ → Na₂SO₄ + 2HCl. In a laboratory the mixture is sometimes warmed; here it is paper only. Hydrogen chloride is a colourless gas that makes white fumes with ammonia, NH₃ + HCl → NH₄Cl. Hydrogen bromide and hydrogen iodide are oxidised by the acid, HBr partly and HI quickly: 2HBr + H₂SO₄ → 2H₂O + SO₂ + Br₂ gives orange-red bromine vapour, and 2HI + H₂SO₄ → 2H₂O + SO₂ + I₂ gives violet iodine vapour. Nitrate gives nitric acid, which breaks down to brown NO₂: 2NaNO₃ + H₂SO₄ → Na₂SO₄ + 2HNO₃, then 4HNO₃ → 2H₂O + 4NO₂ + O₂. Silver nitrate confirms the three halides by colour: AgCl is white (it darkens in sunlight), AgBr pale yellow and AgI yellow; AgCl dissolves in concentrated ammonia, AgBr only slowly, AgI not at all. The book’s paper tests with starch are less clear for bromine, so the vapour colour and the silver result are the reliable evidence. Nitrate is also shown by the brown-ring test: when concentrated acid is layered under a nitrate solution mixed with fresh iron(II) sulphate, a brown ring appears where they meet. It is described here in words only.