Identification of anions

part 1 of 12.5 Identification of ions and gases

Test for carbonate ions CO₃^2-

• react sample with dilute acid

• bubble gas released through limewater

• if limewater turns cloudy, carbonate ion is present

Test for halide ions: Cl^-

• acidify sample with dilute nitric acid

• add aqueous silver nitrate

• a silver halide precipitate forms if a halide ion is present

  • the chloride ion forms a white precipitate of silver chloride

Test for halide ions: Br^-

• acidify sample with dilute nitric acid

• add aqueous silver nitrate

• a silver halide precipitate forms if a halide ion is present

  • the bromide ion forms a cream precipitate of silver chloride

Test for halide ions: I^-

• acidify sample with dilute nitric acid

• add aqueous silver nitrate

• a silver halide precipitate forms if a halide ion is present

  • the iodide ion forms a yellow precipitate of silver chloride

Test for nitrate ions: NO₃^-

• reduce sample with aqueous NaOH and aluminium foil & heat gently

• test for ammonia gas released

  • ammonia turns damp red litmus paper blue if present

Test for sulfate ions: SO₄^2-

• Acidify sample with dilute nitric acid

• Add a few drops of barium chloride solution

• A white precipitate of barium sulfate is formed, if the sulfate ion is present

Test for sulfite ions: SO₃^2-

• Add dilute acid to sample

• Warm the mixture gently

• Bubble the gas released through potassium manganate(VII) solution

• The potassium manganate(VII) solution changes from purple to colourless if the sulfite ion is present