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Separating Mixtures

Chemistry: IB Diploma Higher Level, topic 1.6.5

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:

Simple distillation

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 vapor released passes through a condenser, where the gas cools back into a liquid.
Fractional distillation

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.

Separation Techniques

We can normally separate mixtures and compounds into the elements or compounds that are found in them. We use physical processes to separate them. These processes don't create new chemical substances (there are no chemical reactions). Some separation processes are:

Filtration

Filtration

  • Separates mixtures of insoluble (can't dissolve) solids and liquids.
  • Done by pouring the mixture through filter paper:
  • The insoluble solid is trapped.
  • The liquid runs through the paper and is collected below.
Crystallization

Crystallization

  • Separates solutions into their constituent (different) parts: dissolved solids (solutes) and liquids (solvents).
  • Heat 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.
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.

Test yourself on Separating Mixtures

  • Why is a thermometer used in simple distillation?

  • Which of these techniques separates solutions with more than one type of dissolved solid (solute)?

  • Filtration

  • Chromatography

  • What is Chromatography used to separate?

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