Chemical Analysis | AQA GCSE Chemistry Notes | Topic 8

  • Pure substance: a single element or compound, not mixed with any other substance.
  • Pure elements and compounds melt and boil at specific temperatures.
  • Formulation: a mixture that has been designed as a useful product e.g. paint.
  • Chromatography can be used to separate and identify parts of a mixtures.
  • Chromatography has a stationary phase (paper) and mobile phase (solvent).
  • Some parts of the mixture are more soluble than others, so they travel different distances in the mobile phase.
  • Rf = distance moved by substance/ distance moved by solvent (0 to 1).
  • Tests for gases
    • Hydrogen: burning splint will produce a squeaky pop
    • Oxygen: glowing splint will relight
    • Carbon dioxide: bubble in limewater and shake and it will turn cloudy.
    • Chlorine: use damp litmus paper and it will bleach and turn white.
  • Tests for metal ions
    • Lithium: crimson
    • Sodium: yellow
    • Potassium: lilac
    • Calcium: orange-red
    • Copper: green
  • Sodium hydroxide test (add sodium hydroxide and it forms these precipitates)
    • Aluminium: white
    • Calcium: white
    • Magnesium: white
    • Copper(II): blue
    • Iron(II): green
    • Iron(III): brown
  • Test for carbonates: since acid + metal carbonate forms salt + water + carbon dioxide, react supposed carbonate with acid and then do carbon dioxide test.
  • Halide test: react with silver nitrate (and dilute nitric acid). Forms precipitate.
    • Silver Chloride: white
    • Silver Bromide: cream
    • Silver Iodide: yellow
  • Sulfate test: react with barium chloride solution (and HCl) and it forms a white precipitate.
  • Instrumental methods are an accurate, sensitive and rapid way to detect and identify elements and compounds.
  • Flame emission spectroscopy is an example.
  • The sample is put into a flame and the light given out is passed through a spectroscope.
  • The output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations.