Filtration & Crystalisation

• Filtration is used to separate an insoluble solid from a liquid.
• 'insoluble' means it will not dissolve in liquid
• This is the equipment used for filtration:

  
• What do you need for a filtration?

  • Conical Flask
  • Filter funnel
  • Filter Paper
• The filtrate is the liquid that is able to pass through the filter paper
• Crystallisation is used to separate a soluble solid from a liquid
• 'soluble' means that it dissolves in water
• In crystallisation you must leave the solution for a few days so that water evaporates and you are left with crystals of the solid
• You can speed up crystallisation by slowly heating the water to speed up evaporation. However you must be careful as the heat can destroy the chemical compounds.
• NaCl and Water can be separated by crystallisation
• If we place a solid in liquid and it doesn't dissolve then you have a mixture of a liquid and an insoluble solid.
• If we place a soluble solid in a liquid then it is a solution
• Filtration separates insoluble solids from liquids. Filter paper is commonly used which has lots of tiny holes so that water can pass through, but not solids. We also place our paper in a filter funnel as well, so the mixture is easily poured through it.
• Solutions can not be separated using filtration
• Evaporation

  • Place the solution in an evaporating dish on top of a tripod
  • Slowly heat with a bunsen burner
  • The solvent will start evaporating and the remaining solution will become more concentrated
  • Crystals will start to form
  • All the solvent will disappear leaving dry crystals of the solid
  • Evaporation is quicky and easy but some solids may decompose when they are heated (thermal decomposition)
• Crystallisation

  • Often used for solids susceptible to thermal decomposition
  • Place solution into evaporation dish and heat it
  • Has to be heated gently (perhaps in a water bath)
  • When some solvent has evaporated and some crystals form stop heating it
  • Leave it to cool
  • As it cools more crystals will form as solids are less soluble at colder temperatures
  • Filter out crystals from remaining solution (filtration)
  • Then dry out the crystals by leaving them somewhere warm or in an oven