Chemical analysis

• Formulations


  Mixtures of chemicals designed to create useful products
• Role of each component in a formulation

  • Each component helps to decide the mixture’s overall properties
• Quantity of each component

  • Each chemical component must be present in a precisely measured quantity
• Chromatography


  Separates a mixture into its different components
• 2 phases of chromatography


  • Mobile phase (liquid or gas)
  • Stationary phase (solid or viscous liquid)
• Separation of substances in chromatography

  • Depends on the distribution of a substance across the 2 phases
• A substance is more attracted to the mobile phase


  It moves far
• A substance is more attracted to the stationary phase


  It doesn't move far
• Strength of attraction in chromatography

  • Different components can be equally attracted to a solvent
• Paper chromatography


  Mixtures of soluble substances are separated using a solvent on paper
• Paper chromatography method


  1. Dip chromatography paper

  2. Solvent travels up paper

  3. Substances move at different rates
• Distance travelled in chromatography

  • Components that travel furthest are highly soluble and minimally attracted to the paper
• Different metal ions produce different flame colours when heated strongly
• Flame test procedure


  1. Dip clean wire loop

  2. Put loop in blue flame

  3. Observe and record flame colour
• Flame test colours for metal cations

  • Lithium, Li+: Crimson
  • Sodium, Na+: Yellow
  • Potassium, K+: Lilac
  • Calcium, Ca2+: Orange-red
  • Copper, Cu2+: Green
• If a mixture of ions is present, some flame colours may not be clearly visible
• Metal hydroxide precipitate tests

  Tests for some metal ions that form insoluble metal hydroxides
• Metal hydroxide test example

  Copper sulfate + sodium hydroxide → sodium sulfate + copper hydroxide
• Copper hydroxide forms a blue precipitate
• Coloured precipitates formed by metal ions

  • Aluminium, Al3+: White
  • Calcium, Ca2+: White
  • Magnesium, Mg2+: White
  • Copper(II), Cu2+: Blue
  • Iron(II), Fe2+: Green
  • Iron(III), Fe3+: Brown
• Distinguishing between aluminium, calcium, and magnesium ions

  • Aluminium hydroxide dissolves in excess sodium hydroxide
  • Calcium hydroxide precipitate is unchanged
  • Magnesium hydroxide solution is unchanged
• Ionic equations


  Represent precipitation reactions including only the ions involved in the formation of the precipitate
• Cu2+(aq) + 2OH-(aq) → Cu(OH)2(s) shows the copper ion has a charge of 2+
• Fe3+(aq) + 3OH-(aq) → Fe(OH)3(s) shows three hydroxide ions are needed to react with the Fe3+ ion
• Testing for negatively charged ions

  • Formation of different precipitates allows identification of negatively charged ions
• Testing for carbonate ions

  1. Add dilute acid

  2. Bubbles produced confirm presence

  3. Use limewater to confirm gas is carbon dioxide
• Testing for sulfate ions

  1. Add dilute hydrochloric acid

  2. Add dilute barium chloride solution

  3. White precipitate forms if sulfate ions are present
• Testing for halide ions

  1. Add dilute nitric acid

  2. Add dilute silver nitrate solution

  3. Observe and record precipitate colour
• Halide ion precipitate colours

  • Chloride, Cl-: White
  • Bromide, Br-: Cream
  • Iodide, I-: Yellow
• Method for practical


  1. Carry out tests on each salt

  2. Dissolve solid samples if needed

  3. Record observations carefully
• Flame tests can be carried out as described earlier
• Hydroxide precipitate tests


  1. Add dilute sodium hydroxide solution

  2. Observe and record precipitate colour
• Test for carbonate ions

  1. Add dilute hydrochloric acid

  2. Bubbles produced confirm presence

  3. Use limewater to confirm gas is carbon dioxide
• Test for sulfate ions

  1. Add dilute hydrochloric acid

  2. Add barium chloride solution

  3. White precipitate forms if sulfate ions are present
• Test for halide ions

  1. Add dilute nitric acid

  2. Add silver nitrate solution

  3. Observe and record precipitate colour
• Instrumental methods of analysis rely on machines
• Instrumental methods of analysis

  • Improved speed
  • Accuracy
  • Sensitivity
• Flame emission spectroscopy


  A scientific instrument based on flame testing
• Data from a spectroscope can be used to identify metal ions in a sample
• Data from a spectroscope can be used to determine the concentration of metal ions in dilute solutions