flame tests

• flame tests can be used to identify some metal ions, CATIONS
• method:

  1. place small amount of chemical onto wire mounted in a handle
  2. place the end of this into a blue bunsen burner flame
  3. colour of flame can be used to work out metal ion present
• LITHIUM COMPOUND = CRIMSON FLAME
• SODIUM COMPOUND = YELLOW FLAME
• POTASSIUM COMPOUND = LILAC FLAME
• CALCIUM COMPOUND = ORANGE-RED FLAME
• COPPER COMPOUNDS = GREEN FLAME
• Problem:

  colour of flame test can be difficult to distinguish, especially if there is a low concentration of the metal compound
• problem:

  sample can contain a mixture of metal ions, which masks the colour of the flame
• flame emission spectroscopy is an instrumental method to analyse metal ions in solutions
• in flame emission spectroscopy:

  • the sample of the metal ion is placed into a flame
  • light given out is passed through a spectroscope
  • this creates a line spectrum, the positions of the lines are specific to metal ions
• flame emission spectroscopy ADV

  • can also tell us the concentration of the metal ion
  • as the lines become more intense with higher concentrations
• instrumental method ADV:

  • rapid (faster analysis of samples than flame test)
  • sensitive (will work on even a tiny sample of metal compound)
  • accurate (more likely to identify metal ion correctly than flame test)