1.1.4

Separating Mixtures

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Separation Techniques

We can normally separate mixtures and compounds into the elements or compounds found in them. We use physical processes to separate them - these don't create new chemical substances. Separation processes include:

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Filtration

  • Filtration separates mixtures that contain insoluble (can't dissolve) solids and liquids (which are soluble).
  • Filtration is performed by pouring the mixture through filter paper:
    • The insoluble solid is trapped by the filter paper.
    • The liquid runs through the filter paper and is collected below.
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Crystallisation

  • Crystallisation separates solutions into their different parts: dissolved solids (solutes) and liquids (solvents).
  • Crystallisation is performed by heating the mixture so that the solvent evaporates.
    • Eventually, crystals of the solute (dissolved solids) will form.
    • We can collect the solvent (liquid) by condensing it as it evaporates.
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Chromatography

  • Chromatography separates solutions with a number of different solutes (solids) in the solvent (liquid).
  • Place a drop of the solution to be separated near the bottom of a piece of chromatography paper. Dip the very bottom of the paper into a suitable solvent. The solvent (liquid) moves up the paper and carries the solutes (solids) in the solution with it.
    • Different solutes (solids) move at different speeds, so they separate on the paper.

Distillation

Distillation is a special technique used to separate mixtures of liquids. It uses the different boiling points of liquids to separate them. There are 2 types of distillation:

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Simple distillation

  • Separates 2 liquids with different boiling points.
    • The mixture is heated until the liquid with the lower boiling point starts to boil.
    • The vapour released passes through a condenser, where the gas cools back into a liquid.
  • Simple distillation can also separate a solute from a solvent, when the solvent has a lower boiling point than the solute.
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Fractional distillation

  • Separates lots of liquids with different boiling points.
    • The mixture is slowly heated until the liquid with the lowest boiling point boils and then condenses.
    • Then we increase temperature slowly to collect (boil then condense) the other fractions.

Jump to other topics

1Atomic Structure

2Chemical Bonding

3Quantitative Chemistry

4Chemical Changes

5Energy Changes

6The Rate & Extent of Chemical Change

7Organic Chemistry

8Chemical Analysis

9Chemistry of the Atmosphere

10Using Resources

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