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Science at key stage 3    (Year 7)

Unit 7H: Solutions
Section 8: Is there a limit to the amount of solid that will dissolve in a liquid?

QCA

Objectives
Children should learn:
  • that when a solid is added to a liquid, eventually no more will dissolve
  • that different masses of different solids dissolve in the same volume of a particular solvent
  • that solids can dissolve in liquids other than water

Activities

Outcomes
Children:
  • Present some pupils with a selection of solids, eg salt, bicarbonate of soda, potassium nitrate, and ask them how they could find out whether there is a limit to how much will dissolve in water at room temperature. Ask other pupils to find out whether there is a limit to the amount of solid, eg salt, that will dissolve in different liquids, eg water, ethanol. Discuss with them how they will decide when no more dissolves and suggest that different groups use different volumes of solvent. Bring together results for the same solvent and look for patterns in these. Introduce the terms 'saturated solution' and 'solubility'.
  • state that there is a limit to the amount of solid that dissolves in a particular volume of water
  • describe differences between the amounts of different solids that dissolve in the same volume of water
  • state that some solids dissolve more in some liquids than others

Points to note
  • It is important to clarify with pupils that they are finding out how much of something dissolves, not how fast it dissolves. They are likely to have investigated the latter at key stage 2.

    • Safety

    • ethanol is highly flammable, potassium nitrate is oxidising. Teachers should make sure pupils can handle these and other substances carefully. This activity is not intended to explore variation in solubility with temperature and there is no need to heat the solvents

Sections in this unit

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This unit is divided into sections. Each section contains a sequence of activities with related objectives and outcomes. You can view this unit by moving through the sections or print/download the whole unit.
1. How can we tell whether a liquid is a mixture?
2. How much salt can we get from rock salt?
3. What happens to the solute when a solution is made?
4. How can we separate solvents from solutes?
5. a. How can chromatography separate and identify substances in mixtures?
6. b. How can chromatography separate and identify substances in mixtures?
7. Checking progress
8. Is there a limit to the amount of solid that will dissolve in a liquid?
9. What else affects solubility?
10. Reviewing work