Test for positive ions

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  • Created by: Jasmin
  • Created on: 17-05-13 11:24
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  • Test for positive ions
    • Metals always form positive ions
    • Flame test
      • Small amount of compound to be tested in wire loop
        • Dipped in concentrated hydrochloric acid and heated to clean it first, dipped in acid again before dipping in metal compound
          • Hold loop in blue flame of Bunsen burner
            • Use colour of flame to identify metal ion
      • LITHUIUM: crimson
      • SODIUM: yellow
      • POTASSIUM: lilac
      • CALCIUM: red
      • BARIUM: green
    • Reactions with sodium hydroxide
      • Metal hydroxides insoluble and precipitate out
      • Add few drops of sodium hydroxide solution
      • CALCIUM: white Ca2+ +2OH- = Ca(OH)2
      • COPPER (II): blue Cu2+ + 2OH- = Cu(OH)2
      • IRON (II): green Fe2+ +2OH- = Fe(OH)2
      • ALUMINIUM: white at first but then redissolves to form colourless
        • Al3+ + 3OH- = Al(OH)3 then Al(OH)3 + OH- = Al(OH)4
      • IRON (III): brown Fe3+ + 3OH- = Fe(OH)3
      • MAGNESIUM: white Mg2+ + 2OH- = Mg(OH)2

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