Separating Mixtures

Simple distillation

Used to separate a dissolved solute from a solution. Works because the solvent has a lower boiling point than the solute.

  • Solution is heated; solvent evaporates
  • Solvent gas travels to a condenser where it is cooled and condensed
  • Solvent left in the beaker

Used to separate salt from water.

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Fractional distillation

Used to separate liquids from a mixture of liquids. Works because each liquid has a different boiling point.

  • Mixture is heated until it is a gas
  • Vapour rises up the fractioning column, which is hotter at the top and cooler at the bottom
  • Vapours condense when they reach their boiling point
  • Vapours travel down individual condensers; collected as liquids

Used to separate ethanol and water, or fractions of different fuels from crude oil.

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Filtration

Used to sepatate an insoluble solid from a liquid. Works because pores in filter paper are only big enough for small molecules or dissolved ions to pass through, not large insoluble solid particles.

  • Mixture poured into a funnel lined with filter paper
  • Liquid molecules pass through the paper
  • Solid molecules left behind in the filter paper

Used to separate excess reactant from a solution.

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Crystallisation

Used to produce solid crystals from a solution.

  • Heat solution in an evaporating basin until almost all the solvent has evaporated
  • Let the remaining solution cool
  • Remove excess liquid and leave crystals to dry
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Paper chromatography

Used to separate mixtures of soluble substances. Works because the different substances move up the chromatography paper at different speeds, so they separate.

  • Pencil line drawn on chromatography paper
  • Dyes being tested are spotted along the line
  • Paper lowered into solvent above the pencil line
  • Dyes travel up the paper, producing spots of each substance in their mixture at different heights

Used to find the substances used in dyes, food colouring and plant pigments.

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