preparation and separation techniques 

• chemists often have to carry out reactions and then separate the products from the initial reactants
• when deciding which techniques to use the following must be taken into consideration
• liquid or solid reagents
• how long the reaction takes
• amount of heat required and volatility of liquid reagents
• preparation and separation techniques
  • reflux
  • distillation
  • fractional distillation
  • drying
  • solvent extraction
  • precipitation
  • crystallisation
  • filtration
  • chromatography
• apparatus
  • condenser
  • round bottomed flask
  • heating mantle
  • lab jack
  • anti bumping granules
• reflux
  • allow organic substances with low boiling point to be heated for long periods without loss due to evaporation
  • many organic reactions require heating for long periods in order to maximise the yeild
  • the reaction mixture is places in a flask and a lie big condenser is attached
  • the condenser cools the evaporating vapours returning them to the flask
• precautions
  • use a heating mantle for higher temperatures than boiling water
  • use anti bumping granules to prevent formation of large gas bubbles in the reaction mixture
  • water flow goes in at the bottom of the condenser and out at the top
• distillation
  • used to separate compounds out from a mixture of liquids
  • relies on differences in boiling points
  • liquids are heated until the vapour pressure equals that of atmospheric pressure where the compound starts to boil
  • components of lower boiling point boil first and are collected first
• fractional distillation
  • used to separate several liquids from a mixture
• solvent extraction
  • a way of separating compounds based on their differing solubility in 2 immiscible liquids eg petroleum spirit and water
  • a way of purifying a a substance eg chlorophyll extraction
  • chlorophyll is more soluble in petroleum spirit than water.when it is extracted from pant leaves an acetone/water mixture is used

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