chemical tests

    Cards (20)

      • 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.
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