Pure and Impure

• In advertising the word 'pure' means nothing added
• Pure (chemistry)

  a pure substance contains only 1 element or compound
• To determine whether a substance is pure or impure, you heat it until it boils
• Pure substances boil at one defined temperature
• Impure substances boil over a range, as the different substances that it contains have different melting and boiling temperatures
• The presence of an impurity usually:

  • lowers the melting point
  • raises the boiling point

  The greater the amount of an impurity, the bigger the differences from the true melting and boiling point.
• Formulation

  a mixture that has been designed to produce a useful product - they contain precise specific measured quantities.
• Examples of a formulation:

  • fuel
  • food
  • cleaning products
  • paint
  • medicine
  • fertiliser