8. Chemical analysis

• pure substances contain one type of element or one type of compound. For example, pure water is a compound of hydrogen and oxygen.
• Compounds are two or more elements that are chemically combined
• Mixtures are two or more elements or compounds that are not chemically combined.
• Pure substances have a sharp melting point compared to impure substances which melt over a range of temperatures
• In chromatography the paper is the stationary phase and the solvent is the mobile phase
• Formulations are mixtures of compounds or substances that do not react together
• Formulations produce a useful product with desirable properties and are used to make medicines, detergents, and other useful products
• Test for chlorine

  Place a burning splint at the opening of a test tube and should produce a squeaky pop sound
• Test for oxygen

  Place a glowing splint inside the test tube and should relight the splint
• Test for carbon dioxide

  Pump gas into lime water and it should turn cloudy if CO2 is present
• Test for chlorine

  Damp litmus paper and it should turn bleached then white
• Flame tests

  1. Dip a wire loop into a sample of the solid compound
  2. Place the loop into the flame of the Bunsen burner. Ensure it is a burning flame
• Lithium - red flame
• Sodium - yellow flame
• Potassium - lilac flame
• Calcium - orange flame
• Copper - green flame
• To test for metal ions, sodium hydroxide needs to be added
• Calcium, magnesium and aluminium all form white precipitates when reacted with sodium hydroxide
• Aluminium precipitate dissolves in sodium hydroxide
• Iron(II) and iron (III) and copper (II) all form coloured precipitates when sodium hydroxide is added
• Iron(II) forms a green precipitate
• Iron(III) forms an orange precipitate
• Copper forms a blue precipitate
• Testing for halide ions - add nitric acid

  Chlorine produce white precipitate

  Bromide produces a cream precipitate

  Iodide produces a yellow precipitate
• Testing for sulphates you add dilute HCl and barium chloride
• Testing for carbonates you add dilute HCl
• How flame emission spectroscopy works

  1. A sample is heated in a flame
  2. Electrons in the metal ions are excited by the thermal energy - therefore go up an energy level
  3. When the electrons move into a higher energy level, they release energy in the form of light
  4. The emitted wavelengths of light are analysed instrumentally