Methods of separating and purifying substances

• what is the definition of pure in Chemistry?

  A Substance made up of a single element or compound.
• A pure substance contains a specific and sharp melting point. However, if a substance is a mixture, then it would melt gradually over a range of temperatures. This means that they are impure. A melting point apparatus is used to find the exact melting point of a mixture.
• What is simple distillation used for?

  Simple distillation is used for separating a liquid from a solution.
• What is a method used in a simple distillation experiment?


  Example:

  • Pour seawater into distillation flask.
  • Set up apparatus with condenser connected to cold tap.
  • Heat flask to evaporate water with lowest boiling point.
  • Water vapor condenses in condenser, collected in beaker.
  • Salt remains in distillation flask.

  
• What is fractional distillation used for?

  Fractional distillation is used for separating a mixture of liquids.
• What is a method used in a fractional distillation experiment?


  Example:

  • Put mixture in flask with fractionating column and condenser.
  • Gradually heat flask, liquids evaporate at different temperatures.
  • Liquid with lowest boiling point reaches top of column first.
  • Higher boiling point liquids may start to evaporate but condense and run back down.
  • Raise temperature to collect next liquid once first one is collected.
• What is filtration used for?

  Filtration is used for separating insoluble solids from liquids. You use filter paper, a funnel and a beaker to complete the experiment. The filter paper leaves out the solid residue from the liquid.
• What is crystallisation used for?

  Crystallisation is used to extract a solid dissolved in a liquid mixture by heating it with a Bunsen burner and an evaporating basin.
• What is paper chromatography used for?

  Chromatography is the separation of mixtures of soluble substances by running a solvent (mobile phase) through the mixture on the paper (the paper contains the stationary phase), which causes the substances to move at different rates over the paper.
• What is the mobile phase in chromatography?

  The solvent or liquid that carries the sample through the stationary phase.

  
• What is the stationary phase in chromatography?

  The molecules that cannot move like a solid or thick liquid. (The Paper).
• The components in the mixture separate out as the mobile phase movies through the stationary phase..
• What is the method for setting up a chromatogram?

  • Draw baseline near bottom of paper.
  • Spot mixture on baseline.
  • Dip bottom of paper into solvent in beaker.
  • Place watch glass on beaker to prevent solvent evaporation.
  • Solvent moves up paper, carrying chemicals with it.
  • Chemicals separate, forming spots at different positions.
  • Remove paper before solvent reaches top.
  • Mark solvent front distance in pencil.

  
• In chromatography, a pure substance would move as a single blob; rather than multiple blobs found in a mixture.
• A Chromatogram can help us find the substances in the mixture by comparing it to a standard.
• How do you calculate RF value?

  Distance travelled by needed solute / Distance travelled by solvent.

  
• What is the process for making potable water?

  • Filtration: Wire mesh removes large debris, and gravel and sand beds filter smaller particles.
  • Sedimentation: Iron sulfate or aluminium sulfate is added to clump fine particles, allowing them to settle.
  • Chlorination: Chlorine gas bubbles through water to kill harmful bacteria and microbes.
• Potable water can also be made by distilling sea water, which is a process that removes salt and other dissolved substances from the water.
• During chemical analysis, the water must be 100% pure (deionised) so that the ions and other chemicals do not interfere with the results.
• This is a fractional distillating diagram: