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STATES OF MATTER - properties of gases and liquids (fluids) and solids

16. Using the particle model to compare miscible liquids and immiscible liquids and use of a separating funnel in terms of immiscible liquids (pure or solutions)

Doc Brown's chemistry revision notes: basic school chemistry science GCSE chemistry, IGCSE  chemistry, O level and ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old science students for national examinations in chemistry and also helpful for UK advanced level chemistry students aged ~16-18 and US grades 11-12 K12 honors.


  • A particle model for comparing miscible and immiscible liquids
  • 16a. WHAT HAPPENS TO PARTICLES WHEN TWO LIQUIDS COMPLETELY MIX WITH EACH OTHER?

  • WHAT DOES THE WORD MISCIBLE MEAN?

  • Using the particle model to explain miscible liquids.

  • If two liquids completely mix in terms of their particles, they are called miscible liquids because they fully dissolve in each other.

  • This is shown in the diagram below where the particles completely mix and move at random.

  • The process can only be reversed by fractional distillation.

  • When two liquids (e.g. A and B) fully mix it means the intermolecular forces between the components are similar e.g. A...A, B...B and A...B attractive forces are similar e.g. ethanol and water.

  • Contrast this argument with that for immiscible liquids.

(c) doc b) + (c) doc b) reversible (c) doc b)
  • Homogeneous mixtures
    • A homogeneous mixture (of at least two substances) is a gaseous, liquid or solid mixture that has the same proportions (ratios) of its components throughout a given sample of the material. A homogeneous mixture is uniform in composition throughout the whole sample.
    • Typical examples include miscible liquids.
    • Two miscible liquids e.g. ethanol (alcohol) dissolves in water to make a clear liquid homogeneous mixture.
    • Petrol is a homogeneous mixture of several hydrocarbon liquids.

  • 16b. WHAT HAPPENS TO PARTICLES WHEN TWO LIQUIDS DO NOT MIX WITH EACH OTHER?

  • WHAT DOES THE WORD IMMISCIBLE MEAN?

  • WHY DO THE LIQUIDS NOT MIX?

  • Using the particle model to explain immiscible liquids.

  • If the two liquids do NOT mix, they form two separate layers and are known as immiscible liquids, illustrated in the diagram below where the lower purple liquid will be more dense than the upper layer of the green liquid.

    • You can separate these two liquids using a separating funnel, the lower layer of the 'purple' liquid will be the more dense substance of the two.

    • The reason for this is that the interaction between the molecules of one of the liquids alone is stronger than the interaction between the two different molecules of the different liquids.

    • When two liquids (e.g. A and B) do NOT mix it means the intermolecular forces between the components are NOT similar e.g. some significant variation between the A...A, B...B or A...B attractive forces are NOT similar e.g. oil and water.

    • Contrast this argument with that for miscible liquids above.

    • For example, the force of attraction between water molecules is much greater than either oil–oil molecules or oil–water molecule attractions, so two separate layers form because the water molecules, in terms of energy change, are favoured by 'sticking together'.

(c) doc b) (c) doc b)

3d. How a separating funnel is used

1. The mixture is put in the separating funnel with the stopper on and the tap closed and the layers left to settle out.

2. The stopper is removed, and the tap is opened so that you can carefully run the lower grey layer off first into a beaker (purple in particle diagram).

3. The tap is then closed again, leaving behind the upper yellow layer liquid (green in particle diagram), so separating the two immiscible liquids.

This separating funnel technique is used in organic chemistry, using an immiscible (with water) organic solvent to extract an organic compound from an aqueous reaction mixture.
  • Heterogeneous mixtures
    • A heterogeneous mixture (of at least two substances) is a mixture in which the composition is not uniform throughout the whole sample of the material mixture.
    • e.g. a mixture of two immiscible liquids e.g. oil and vinegar in salad dressing, would be an example of a heterogeneous mixture no matter how much you shake before use.

Learning objectives for miscible and immiscible liquids

Know that when two liquids completely mix and dissolve giving a homogeneous mixture in each other they are described as miscible liquids.

When two liquids cannot mix together, i.e. cannot dissolve in each other, they are described as immiscible liquids.

Know that liquids like petrol are a mixture of miscible hydrocarbon liquids.

Know that oil and water are immiscible liquids and oil forms a separate layer on water.

Know that the less dense liquid floats on top of the more dense immiscible liquid.

Be able to describe how a separating funnel can be used to separate two immiscible liquids.


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Detailed notes on the states of matter and their properties

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