Sc2b- Filtration and crystallisation

• Mixtures that can be separated by filtration

  • Crystals and a solution after crystallisation
  • Water from sea water
• Mixtures that can be separated by crystallisation

  • Sodium chloride from salt solution
  • Copper sulphate and water
• What is a solvent?

  The liquid in which a solute dissolves
• What is a solute?

  The substance that dissolves in a liquid to form a solution
• What is the solution?

  The mixture formed when a solute has dissolved in a solvent
• What is insoluble?

  Describes a substance that will not dissolve
• What is filtration?

  Technique that seperates substances that are insoluble in a solvent from those that are soluble using a filter
• What is crystallisation?

  A technique of heating a solution to evaporate the solvent, leaving the solutes behind. The solutes then become crystals
• What are the steps of crystallisation?

  1. The solution is heated to remove enough solvent to produce a saturated solution
  2. The saturated solute is allowed to cool
  3. Crystals form in the solution
  4. The crystals are separated from the liquid and dried.
• What is a saturated solution?

  A solution where no more solute can be held
• What gives more control when heating?

  A hot water bath allows more precise control
• Crystallisation equipment

  Gauze, evaporating bath, tripod

  
• What is solubility?

  The mass of solute that dissolves in a given a volume of solvent at a given temperature.
• Why does crystallisation work?

  The solubility of the solute decreases as the saturated solution cools

  • crystals form from the excess solute
• Ways to remember:

  
• Filtration equipment

  
• What are the reasons for filtration?

  -Purify a solution by removing solid impurities

  -Seperate the solid you want from the liquid it is mixed with
• Why does filtration work?

  Because the filter paper has tiny pores that are large enough for water/ dissolved substances but are too small for insoluble solids
• Explain how mixtures are seperates by filtration

  -solvent and solutes pass through fine holes in the filter paper to form filtrate

  -Bits of insoluble substances cannot fit through the holes so they leave a residue in the filter paper
• Risks of crystallisation and how to reduce them

  -Risks of spitting —> reduced by wearing eye protection, evaporating bain gently with steam or removing the bunsen burner before the solution is completely dry

  -Risks of solvent being hazardous —> Handle with care, or allow for a free flow of air
• What is thermal decomposition?

  Solids that can be broken down into something else using heat
• What is the disadvantage of evaporation?

  Solids can decompose when it is heated (thermal decomposition)
• Crystallisation is used to prevent thermal decomposition