Science at key stage 3    (Year 7)

• name some solids that dissolve in water and some that do not
• identify the components of some mixtures, eg seawater is water with salt and other solids dissolved in it
• describe one way of separating the components of a mixture

• plan a method for obtaining a sample of salt from rock salt
• obtain a sample of salt
• explain why the mass of the salt sample was less than the mass of rock salt
• explain in terms of the original sample or in terms of techniques why results of different groups differ

• 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

• describe how the solvent could be separated from the solute by heating the solution, followed by cooling
• explain that separation works because the solvent changes to a gas and back to a liquid, but the solute does not

• use chromatography to separate and identify different solutes
• use particle ideas to explain how chromatography works

• interpret chromatograms, explaining what the evidence shows
• describe a situation in which chromatography provides useful evidence

• show by modelling how particles behave in some changes
• describe what the models show, eg when marble is added to water it doesn't break up into smaller particles, so the particles can't mix together

• 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

• 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

• match the correct explanation to each change
• identify, with reasons, incorrect explanations
• summarise key points about changes and techniques in the unit