Chemical analysis

• A pure substance is made of only one type of compound or element.
• A chemically pure substance will boil at a specific temperature. Impurities in the substance will lower the melting point and increase the melting range.
• Impurities in a substance will increase the boiling point and range of temperatures.
• Formulations are mixtures made using a formula. Each component is in a measured quantity and is added to the mixture in a precise ratio.
• Formulations are really important in the pharmaceutical industry. In everyday life, they are products like paint, cleaning products, fuels, cosmetics, fertilisers, metal alloys and foods.
• Chromatography uses two phases: the mobile and stationary phase
• In paper chromatography, the mobile phase is water and the stationary phase is the filter paper
• During chromatography, the substances in a sample constantly move between the mobile and stationary phase and an equilibrium is formed.
• In chromatography, the chemicals that spend more time in the mobile phase travel further. The amount of time spent in each phase depends on how soluble they are in the solvent, and how attracted they are to the stationary phase.
• The Rf value is:

  distance travelled by substance / distance travelled by solvent
• The Rf value changes depending on the solvent used.
• Tests for gases:

  • Chlorine - bleaches damp litmus paper
  • Oxygen - relights a glowing splint
  • Carbon dioxide - makes limewater cloudy when bubbled through
  • Hydrogen - causes a 'squeaky pop' when a lit splint is held near
• To test for carbonates, add dilute acid and bubble through limewater. The limewater will turn cloudy if a carbonate is present.
• To test for sulfates, add dilute hydrochloric acid and barium chloride. A white precipitate of barium sulfate will form if sulfates are present.
• To test for halides, you add dilute nitric acid and silver nitrate solution.

  • A chloride produces a white precipitate
  • A bromide produces a cream precipitate
  • An iodide produces a yellow precipitate
• In a flame test:

  • Lithium burns crimson
  • Sodium burns yellow
  • Potassium burns lilac
  • Calcium burns orange-red
  • Copper burns green
• To do a flame test, dip a platinum loop of wire into HCl to clean it and then hold it in a flame. Then dip it into the solution you want to test and hold that in the flame and observe the colour change.

  This only works for solutions with one metal ion.
• In a sodium hydroxide test:

  • Calcium (Ca2+) forms a white precipitate
  • Copper II (Cu2+) forms a blue precipitate
  • Iron II (Fe2+) forms a green precipitate
  • Iron III (Fe3+) forms a brown precipitate
  • Aluminium (Al3+) forms a white precipitate
  • Magnesium (Mg2+) forms a white precipitate
• The white precipitate produced by aluminium (Al3+) redissolves in excess sodium hydroxide to produce a colourless solution.
• During flame emission spectroscopy, a sample is placed in a flame and their electrons become 'excited'. When they drop back to their original energy levels, they emit light which is measured through a spectroscope.
• Each ion produces a different wavelength of light, so a different line spectrum. This can be used to identify them.
• Flame emission spectroscopy also works for mixtures.