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

15. A particle model of dissolving a solid (solute) in a solvent to give a solution

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.


15. Dissolving solids and solution formation

(c) doc b) + (c) doc b) reversible (c) doc b)
  • 3a. WHAT HAPPENS TO PARTICLES WHEN A SOLID DISSOLVES IN A LIQUID SOLVENT?

  • What do the words SOLVENT, SOLUTE and SOLUTION mean?

  • When a solid (the solute) dissolves in a liquid (the solvent) the resulting mixture is called a solution.

    • In general: solute + solvent == dissolving ==> solution

    • So, the solute is what dissolves in a solvent, a solvent is a liquid that dissolves things and the solution is the result of dissolving something in a solvent.

    • The solid loses all its regular structure and the individual solid particles (molecules or ions) are now completely free from each other and randomly mix with the original liquid particles, and all particles can move around at random.

    • This describes salt dissolving in water, sugar dissolving in tea or wax dissolving in a hydrocarbon solvent like white spirit.

    • It does not usually involve a chemical reaction, so it is generally an example of a physical change.

    • Whatever the changes in volume of the solid + liquid, compared to the final solution, the Law of Conservation of Mass still applies, no loss or gain of the total mass of the system.

    • This means:

    • mass of solid solute + mass of liquid solvent = mass of solution after mixing and dissolving.

    • You cannot create mass or lose mass, but just change the mass of substances into another form.

    • If the solvent is evaporated, then the solid is reformed e.g. if a salt solution is left out for a long time or gently heated to speed things up, eventually salt crystals form, the process is called crystallisation.

  • 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 solutions e.g. aqueous solutions of soluble salts are homogeneous mixtures.

Learning objectives for a particle models of solution formation

Be able to describe with particle model diagrams the difference between a solid, liquid and a solution.

Know what is meant by the words solvent, solute and solution and relate them to the particle model.

Know that the law of conservation of mass applies to the preparation of a solution (no loss or gain in mass, nothing disappears!).

Know what is meant by a homogeneous mixture i.e. here all the solid dissolves without any undissolved solid left over.


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INDEX of all my notes on the states of matter

(GCSE level and advanced pre-university level revision notes)

Detailed notes on the states of matter and their properties

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