Test for positive ions
- 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
- Hold loop in blue flame of Bunsen burner
- Dipped in concentrated hydrochloric acid and heated to clean it first, dipped in acid again before dipping in metal compound
- LITHUIUM: crimson
- SODIUM: yellow
- POTASSIUM: lilac
- CALCIUM: red
- BARIUM: green
- Small amount of compound to be tested in wire loop
- 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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