chemical tests

• • Flame tests are used to identify certain metal ions in compounds.
• • In a flame test, a clean platinum or nichrome wire is dipped into a sample and then placed in a flame.
• • The flame will change colour depending on the metal ion in the sample.
• lithium flame

  crimson red
• sodim flame


  yellow
• potassium flame


  lilac
• calcium flame

  orange-red
• barium flame


  green
• copper flame


  blue-green
• • Sodium hydroxide (NaOH) reacts with many metal ions to form insoluble hydroxides.
• NAOH

  • This can be used to help identify the metal ion in an unknown sample.
  • Aluminium (Al), calcium (Ca), and Magnesium (Mg) produce a white precipitate, and iron (II) and iron (III) form green and brown precipitates respectively.
  • Copper (Cu) ions produce a blue precipitate, zinc (Zn) - a white precipitate, and lead (Pb) - a white precipitate which dissolves in excess NaOH.
• • To test for ammonium ions (NH4+), heat the sample with sodium hydroxide solution.
• • If ammonium ions are present, ammonia gas (NH3) will be released.
  • The ammonia can be detected by its characteristic strong, pungent smell.
  • Also, it turns damp red litmus paper blue.
• • To test for a carbonate, add dilute acid to the sample.
• • If carbonate ions are present, the reaction will produce carbon dioxide gas that can be tested with limewater which turns cloudy due to formation of calcium carbonate.
• • To test for a sulfate, add dilute hydrochloric acid and barium chloride solution to the sample.
• • If sulfates are present, a white precipitate of barium sulfate will form.
• • To test for halide ions (Cl-, Br-, I-), add dilute nitric acid and silver nitrate solution to the sample.
• • Chlorides, bromides, and iodides will form a precipitate with colours white, cream, and yellow respectively.
• • Chlorine water bleaches damp litmus paper, bromine water gives orange solution, iodine solution forms a blue-black complex with starch.