RP4-Identification of cations and anions

• To test for group 2 cations, use either sodium hydroxide, dilute sulfuric acid or an ammonium solution with barium, calcium, magnesium and strontium chloride.
• When testing for group 2 cations with sodium hydroxide, barium chloride stays as a colourless solution and calcium, magnesium and strontium chloride form white precipitates.
• Barium, calcium, magnesium and strontium chlorides are all colourless solutions.
• When testing for group 2 cations with sodium hydroxide, adding an excess does not affect the result.
• When testing for group 2 cations with dilute sulfuric acid, barium, calcium, magnesium and strontium chloride will all form white precipitates.
• When testing for group 2 cations with sulfuric acid, adding an excess causes magnesium chloride to form a colourless solution, but has no affect on barium, calcium or strontium chloride.
• When testing for group 2 cations with an ammonium solution, magnesium chloride will form a white precipitate but barium, calcium and strontium chlorides will have no visible change.
• When testing for ammonium ions, mix equal amounts of ammonium chloride and sodium hydroxide, and warm gently with a water bath. Test fumes released using damp litmus paper which will turn from red to blue.
• When testing for group 7 anions, use either silver nitrate then dilute and concentrated ammonia or concentrated sulfuric acid with potassium chloride, potassium bromide and potassium iodide.
• When testing for group 7 anions using silver nitrate, add nitric acid first to remove any ions that may form a different precipitate. Potassium chloride forms a white precipitate, potassium bromide a cream precipitate and potassium iodide a yellow precipitate.
• When testing for group 7 anions using dilute ammonia after using silver nitrate, potassium chloride produces a colourless solution, and potassium bromide and iodide have no visible change.
• When testing for group 7 anions using concentrated ammonia after silver nitrate, potassium chloride and bromide becomes colourless solutions and potassium iodide has no visible change.
• When testing for group 7 anions using sulfuric acid, potassium chloride produces white fumes, potassium bromide produces orange fumes and potassium iodide produces purple fumes and a purple solid. They all turn blue litmus paper red.
• To test for hydroxide ions use red litmus paper on sodium hydroxide, and it will turn blue.
• To test for carbonate ions, add hydrochloric acid to sodium carbonate solution and bubble the gas produced through limewater, which will turn cloudy.
• To test for sulfate ions, add hydrochloric acid first to remove any other compounds that may react, and then add barium chloride to the solution which will form barium sulfate. Add more hydrochloric acid. If the solution doesn't dissolve, sulfate ions are present.
• Safety: barium chloride is toxic - wear a lab coat and eye protections; concentrated ammonia is corrosive - wear gloves, a lab coat and eye protection and use a fume cupboard; nitric acid is an irritant - wash hands if spilled; concentrated sulfuric acid is corrosive, and fumes produced are toxic and corrosive - use as small an amount as possible, use a fume cupboard, wear a lab coat, goggles and gloves.