Filtration & Crystallisation

• What are the 6 methods through which mixtures can be seperated?

  Filtration, chromatography, crystallisation, evaporation, simple distillation and fractional distillation
• What is filtration used for?

  To separate insoluble solids from liquids
• What is the technique for filtration?

  Place a piece of filter paper in a funnel, and put the funnel over a breaker. Pour your mixture through the funnel. Any insoluble solids will be caught by the filter paper, we call this the residue. Any liquid or dissolved substances will pass straight through, we call this the filtrate
• What is evaporation used for?

  To separate a dissolved solid from a liquid
• What is the technique for evaporation?


  Heat your solution until all of the solvent evaporated, and only solids remain. (this is normally done by placing the solution in an evaporating dish on a tripod, and heating it with a bunsen burner)
• What is crystallisation used for?

  To separate a soluble substance from a solvent
• What is the technique for crystallisation?

  Pour the solution into an evaporating dish. Heat it using a Bunsen burner. Stop heating it when crystals start to form (‘point of crystallisation‘) and allow it to cool down. Either leave it to allow the rest of the water to evaporate, or filter out the crystals using filter paper and a funnel. Dry the crystals in a warming oven or desiccator
• What is the benefit of using crystallisation rather than evaporation as a separating technique?

  The excess heat used in evaporation can sometime cause the crystals to break down by thermal decomposition
• How would you isolate the sand and salt from a mixture of salt and sand?

  Place the mixture in water and stir. The salt will dissolve but the sand won’t. Pour the mixture through filter paper and funnel. The sand will get stuck on the filter paper. Evaporate the water by heating. This will leave behind the salt
• What is chromatography used for?

  Separates the components of a mixture based on their solubility
• What is a ’pure’ substance?

  A substance that only contain one type of element or compound
• What is a solution?

  A mixture that contains absolute (the solid) dissolved in the solvent (the liquid)
• What do ‘soluble‘ and ’insoluble’ mean?

  A soluble substance is one that can dissolve in liquid. An insoluble substance is one that cannot dissolve in liquid