- Show pupils a beaker of water of a particular mass,
eg 100g, and ask them to predict what the total mass will be if some salt,
eg 4g, is dissolved in the water, and to test their predictions by weighing. Ask them to explain why the mass remains the same and to say how much salt they would expect to get if they evaporated the water.
- Remind pupils of work they did on particles in solids and liquids in unit 7G 'Particle model of solids, liquids and gases', referring back to the annotated diagrams drawn at the end of the unit.
- Show a model or models,
eg
ICT simulation, mixing rice and peas, to illustrate the mixing of particles when a solid dissolves in a liquid, asking pupils to put in their own words what is happening.
- Ask pupils to draw the water particles before and after the addition of salt and to use these to explain,
eg that mass is conserved, why filtering will not separate the salt.
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- state that the mass of a solution is the same as the mass of the solute and solvent,
eg if you dissolve 5g of salt in 200g of water, you'll get 205g of salt solution
- describe,
eg using annotated diagrams, how solute and solvent particles mix
- explain that as the particles mix no matter is lost, so the mass remains the same
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