TESTING FOR CATIONS

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  • TESTING FOR CATIONS
    • FLAME TESTS
      • Potassium (K+) --> lilac flame
      • Calcium (Ca2+) --> brick red flame
      • Lithium     (Li+)  --> red flame
      • Sodium  (Na+) --> orange flame
      • How to do a flame test
        • 2. Hold the wire in a flame and it should burn with no colour
        • 1. Get a wire loop and clean it by dipping it into some dilute hydrochloric acid
        • Then you can dip the loop into the sample you want to test and put it back in the flame
    • IDENTIFYING METAL CATIONS
      • COPPER (II)
        • blue precipiate
        • Cu2+ + 2OH- ---> CU(OH)2
      • IRON (II)
        • sludgy green precipitate
        • Fe2+ + 2OH- ---> FE(OH)2
      • IRON (III)
        • Fe3+ + 3OH- ---> FE(OH)3
        • red/brown precipitate
      • Many metal hydroxides are insoluble and precipitate out of solution when formed
        • Some of these hydroxides have a characteristic colour which you can see if you add a few drops of sodium hydroxide solution
    • TESTING FOR AMMONIUM IONS
      • TEST: add sodium hydroxide to the solid or solution being tested
      • RESULT: if ammonium ions are present then a pugnent smelling gas is produced
        • The gas produced is called ammonia gas (NH3)
          • When ammonia gas is present, it turns damp red litmus paper blue

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