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CHEMISTRY · Stage 7 · Chapter 2: Elements, Compounds and Mixtures

Chemistry 2.10 What’s in a solution? — Solutes, Solvents and Dissolving

5 min read 6 parts Lesson 10 of 13

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Lesson summary

2.10 What's in a solution?

  • Arrangement
  • Dissolving
  • Rice and beans model
  • Limitations
  • Prediction
  • Conclusion

Part 1 of 6What a solution is

1Solution1 point
= a mixture that forms when a substance dissolves in a liquid.
  • All parts of a solution are the same throughout.
2Solvent
= the liquid in a solution.
3Solute
= the substance that dissolves in a solution.
4Example1 point
— in coffee made with hot water, coffee powder and sugar dissolve in the water.
  • In a solution of sugar in water the solute is sugar and the solvent is water.

Part 2 of 6Soluble and insoluble

  • Soluble able to dissolve in a liquid, for example sugar and salt in water.
  • Insoluble not able to dissolve in a liquid, for example sand and chalk in water.

Part 3 of 6Particles in a solution

  • Arrangement — particles of the solute and solvent are mixed randomly, and they move around, sliding over each other.
  • Molecules — a water molecule has one oxygen atom joined to two hydrogen atoms.
    • A sugar molecule has 12 carbon atoms, 22 hydrogen atoms and 11 oxygen atoms.
  • Dissolving — the solute does not disappear, because it spreads out as separate particles among the solvent particles.

Part 4 of 6Modelling solutions

  • Rice and beans modelrice grains represent water particles and beans represent sugar particles.
  • Strengthit shows that two types of particle are mixed together and spread out.
  • Limitationsrice and beans are much bigger than real particles, they are solid and do not show real attraction between particles.

Part 5 of 6Why a solution is a mixture

  • The solution contains particles of more than one substance that are not joined together.
  • The amounts of the substances in the solution can change.
  • It is easy to separate the water and sugar, by letting the water evaporate.
  • The substances in the solution keep their own properties, for example the sugar can still be tasted.

Part 6 of 6Investigating what happens to the sugar

  1. Find the mass of a beaker of water.
  2. Weigh out 10 g of sugar.
  3. Add the sugar to the water and stir until it dissolves.
  4. Find the mass of the beaker and its solution.
  • Predictionthe total mass at the start will equal the mass of the beaker and solution at the end, because there are the same number of water and sugar particles before and after mixing.
  • Resultthe masses were equal, for example 200 g + 10 g = 210 g at the start and 210 g at the end.
  • Conclusionall the sugar dissolves and the sugar particles have not disappeared.
  • Limitationonly one solute, sugar, was investigated, so the same conclusion may not be true for other solutes such as salt.

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