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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

Use of a separating funnel in terms of immiscible liquids (pure or solutions)

X-reference on fractional distillation to separate a miscible liquid mixture

[Author © Dr WP Brown PhD: Doc Brown's chemistry exam revision notes on states of matter - physical properties of gases, liquids and solids, suitable for students of UK GCSE level and international IGCSE/O level chemistry courses, ~US grades 9-10 chemistry notes [page updated Nov 30th 2025]

INDEX of all my notes on the states of matter

GCSE (~US grades 8-10) level multiple choice QUIZ on the states of matter: gases, liquids & solids

  • 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.

  • This constitutes a homogeneous mixture.

  • If two liquids completely mix in terms of their particles in all proportions, they are called miscible liquids because they fully dissolve in each other i.e. the moving particles randomly mix on shaking to give a homogeneous solution of one liquid dissolved in the other (or vice versa!) since its all the same in  the end.

  • 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 bonding 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.
    • You can separate a homogeneous mixture of liquids using fractional distillation.

    • You can also separate miscible liquids using a gas-liquid chromatography.

  • 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

  • BUT still a mixture, but not homogeneous

  • 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'.

    • You can separate two immiscible liquids (can be both mixtures) using a separating funnel.

(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.

Key points about the Kinetic Particle Model:

Miscible versus immiscible Liquids

Core Explanation

  • Miscible liquids:
    • Liquids that mix completely in all proportions.
    • Their particles are similar in polarity/forces, so they attract each other and intermingle.
    • Example: ethanol + water → particles mix evenly due to hydrogen bonding.
  • Immiscible liquids:
    • Liquids that do not mix; they form separate layers.
    • Their particles have very different intermolecular forces, so they do not attract each other.
    • Example: oil + water → oil particles are non-polar, water particles are polar, so they separate.

Kinetic particle model explanation:

  • Particles in liquids move randomly and collide.
  • If intermolecular forces are compatible, particles intermingle (miscible).
  • If forces are incompatible, particles cluster with their own kind, forming separate layers (immiscible).

Separation Methods

Mixture Type Separation Method Explanation (Particle Model) Example
Miscible liquids Fractional distillation Different liquids have different boiling points. Heating gives particles enough energy to escape as vapour; vapours condense separately. Ethanol + water
Immiscible liquids Separating funnel (decanting) Liquids form distinct layers due to density differences; particles of each liquid stay together. Oil + water
Miscible liquids with close boiling points Chromatography (advanced contexts) Solvent particles carry solute particles differently depending on attraction. Ink mixtures

Typical Board-Specific Requirements

Key Focus Notes
Particle model, miscibility, separation Stress diagrams of miscible versus immiscible
Solubility, miscibility, distillation Link miscibility to intermolecular forces
Kinetic particle theory, separation methods Clear particle diagrams expected
Solutions, miscibility, distillation Practical focus: fractional distillation
Miscibility, immiscibility, separation Link to industrial fractional distillation
Particle theory, miscibility, separation Emphasise random motion and forces
Miscibility, immiscibility, separation Focus on everyday examples (oil/water, ethanol/water)

Student Exam Tips about miscible and immiscible liquids

  • Draw particle diagrams: Show miscible liquids with mixed particles, immiscible with separate clusters/layers.
  • Use keywords: "random motion," "intermolecular forces," "miscible," "immiscible," "fractional distillation," "separating funnel."
  • Always state why: Miscible = similar forces; immiscible = different forces.
  • Link to practicals: Fractional distillation for miscible, separating funnel for immiscible.
  • Mention density differences: For immiscible liquids, the less dense liquid floats.

Typical Misconceptions about miscible and immiscible liquids

  •  “Immiscible liquids cannot be separated” → Correction: They can be separated using a separating funnel.
  •  “Miscible liquids always have the same boiling point” → Correction: They may have different boiling points, allowing fractional distillation.
  •  “Oil dissolves in water” → Correction: Oil and water are immiscible; they form layers.
  •  “Fractional distillation works for immiscible liquids” → Correction: It is used for miscible liquids with different boiling points.
  •  “Liquids stop moving once mixed” → Correction: Particles continue moving randomly due to kinetic energy.

Quick Revision Overlay for miscible and immiscible liquids

  • Miscible liquids: Mix completely → separated by fractional distillation.
  • Immiscible liquids: Form layers → separated by separating funnel.
  • Particle model: Random motion + intermolecular forces explain mixing or separation.

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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extra advanced notes on gas laws, ideal and non-ideal gasesWebsite content © Dr Phil Brown 2000+. All copyrights reserved on Doc Brown's Chemistry revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. GCSE level and advanced pre-university level revision notes. Detailed notes on the states of matter and their properties. Based on the syllabus-specifications for students taking the IGCSE/GCSE level physics examinations summary revision notes and key points about using the kinetic particle model to explain miscible liquids and immiscible liquids, for students taking the WJEC gcse chemistry/physics, CCEA gcse chemistry/physics, CIE igcse chemistry/physics, AQA igcse/gcse physics, Edexcel gcse chemistry/physics, OCR 21st century chemistry/physics, OCR gateway chemistry/physics or any other GCSE or IGCSE level chemistry/physics exams e.g. US grade 9-10 physics courses

INDEX of all my notes on the states of matter

GCSE (~US grades 8-10) level multiple choice QUIZ on the states of matter: gases, liquids & solids

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