The Chemist's tools 9.1.8 - Pure substances and mixtures


Students should:

  • Know the definition of a mixture
  • Be able to identify the components of simple mixtures
  • Know the techniques of filtration, simple distillation, fractional distillation, decanting and chromatography


Matter: states and properties of matter.

Particle/kinetic theory, diffusion.

Pure and impure substances. Types of mixtures (solutions, oils, alloys, emulsions)

Separation techniques, including filtration, distillation [including crude oil - myp10], chromatography.

Student activity

Separation techniques circus.

  • Filtration
  • Distillation
  • Fractional distillation (teacher lead)
  • Paper chromatography
  • Column chromatography
  • Decanting
  • Physical separation

Student follow-up

Find examples from everyday life for each of the following types of mixtures:

  • Solid - solid
  • Solid - liquid
  • Liquid - liquid
  • Liquid - gas
  • Gas - gas
  • Solid - gas

And suggest which of the techniques learned could be applied to separate each mixture.

Students should research the following terms:

  • Colloid
  • Emulsion
  • Suspension
  • Alloy

They should describe each type of mixture and give two examples from everyday life.

Teacher's notes

A colloidal system is one with components of one or two phases – gas, liquid or solid. In a relatively straightforward system there are two components, one of which is being dispersed and the other known as the continuous medium.

Colloids bridge the gap between solutions and suspensions.

They represent a type of mixture intermediate between a homogeneous mixture (also called a solution) and a heterogeneous mixture, and have properties that are also intermediate between the two.

The size of dispersed phase particles in a colloid range from one nanometre (1 x 10-9 m) to one micrometre (1 x 10-6 m).

Colloids can be classified according to the phases involved.

Liquid in gas: often known as an aerosol – e.g. mist
Solid in gas: this is a smoke – e.g. dusty air, smoke from a bonfire

Gas in liquid: this is a foam – e.g. whipped cream
Liquid in liquid: this is an emulsion – e.g. blood, mayonnaise, milk
Solid in liquid: this is a sol – e.g. paint, starch ‘solution’, the iron(III) oxide seen in this demonstration

Gas in solid: this is usually known as a solid foam – e.g. pumice, expanded polystyrene foam
Liquid in solid: this is a gel – e.g. gelatine, jelly, many types of cheese
Solid in solid: this is a solid sol – e.g. coloured glass

Notice that ‘gas in gas’ is not on the list. This is because all gases are ‘soluble’ in each other and thoroughly mix to give a homogeneous system.

Adapted from


Separation techniques circus

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