Science at key stage 3 (Year 7)
Unit 7H: Solutions
Section 9: What else affects solubility?
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Objectives |
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- that many solutes are more soluble at higher temperatures
- to use tables of data to calculate quantities of material to use
- to make comparisons, identify patterns and make predictions from graphs
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Activities |
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Outcomes |
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Children: |
- Ask pupils to suggest what else affects how much solid dissolves in a liquid, perhaps showing them a saturated solution,
eg of benzoic
acid, which forms crystals as it cools. Provide pupils with a table of data showing approximate solubilities of solutes at different temperatures. Help them to work out how much they would need to dissolve in 10g of water to make a saturated solution at a particular temperature. Ask pupils to prepare a warmed solution with a suitable amount of solid and to cool it down to identify the temperature at which crystals appear. Put together class results and help pupils to draw a graph showing how solubility varies with temperature and to describe what the graph shows and what the solubility might be at other temperatures.
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- state that a saturated solution has been formed when crystals appear
- state the solubility at a particular temperature,
eg at 70C, 3g of the solid dissolved in 10g of water
- describe the way in which the solubility of the solute varies with temperature
- use the pattern of solubility data to predict solubility at higher and lower temperatures
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Points to note |
- Pupils are likely to have used a variety of thermometers in key stage 2 and this is extended in unit 7I 'Energy resources'.
- As in the previous activity, it is important to draw the distinction between 'how much' and 'how fast'.
- This activity works well using potassium chloride, potassium bromide or potassium iodide as the solute.
- Extension: pupils could look at previously prepared data about the variation of solubility with temperature of a wider range of solutes, and identify simple patterns and make predictions from these.
Safety
- remind pupils how to heat test tubes of chemicals
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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.
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