Purity, formulations and chromatography

• Pure substance


  A single element or compound, not mixed with any other substance
• Pure substances


  • They melt and boil at specific temperatures
  • Melting and boiling point data can be used to distinguish pure substances from mixtures
• Pure substance (in everyday language)


  Substance that has had nothing added to it, so it is unadulterated and in its natural state
• Formulation


  Mixture that has been designed as a useful product

  • for example: fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods
• Many products are complex mixtures in which each chemical has a particular purpose
• Making formulations


  Mixing the components in carefully measured quantities to ensure the product has the required properties
• Chromatography


  Used to separate mixtures and give information to help identify substances
• Chromatography


  • Involves a stationary phase and a mobile phase
  • Separation depends on the distribution of substances between the phases
• Rf value


  Distance moved by substance ÷ distance moved by solvent
• Different compounds have different Rf values in different solvents, which can be used to help identify the compounds
• Compounds in a mixture may separate into different spots depending on the solvent but a pure compound will produce a single spot in all solvents
• Paper Chromatography


  Analytical technique separating compounds by their relative speeds in a solvent as it spreads through paper
• Pigment


  Solid, coloured substance
• The more soluble a substance is, the further up the paper it travels
• Paper chromatography separates different pigments in a coloured substance