C2a Mixtures C3.1 Explain the differences 1) Begin by displaying a Students record the melting Ensure that students between a pure substance and scanning tunnelling temperature of ice over time fully understand the a mixture electron microscope and compare this with the differences between image of some atoms as melting temperature of an pure substances and students come in. salt mixture. Students should mixtures before moving Interpret melting point data to C3.2 distinguish between pure Challenge students to observe that the temperature of on to look at their write one sentence pure ice does not change as the melting points. substances which have a sharp indicating whether they ice is melting, but the melting point and mixtures think the image shows a temperature of the impure ice which melt over a range of Discuss with the class pure substance or a does. temperatures what happens to the mixture, and explaining physical arrangement how they can tell. Equipment: 250 cm3 beaker, of particles during 5 ice cubes, 100 g (NaCl), melting. A reasonable thermometer or thermocouple 2) Ask students to match focus might be the (ideally with a lower range to four materials (diamond, ordering of particles −20°C), stop clock, mass nitrogen, ice and gold) and their separation. balance with their melting points in °C (3550, -210, 0, Digital: Pure 1063). substances and mixtures video C2b Filtration C3.3 Explain the experimental 1) Hold up pieces of The aim of the investigation is Demonstrate how to and crystalisation techniques for separation of apparatus and ask what to identify which of three heat to dryness safely. mixtures by each one is. Ask students samples of rock salt contains Use the demonstration ... to explain or show how the largest quantity of salt. to compare the crystal c filtration they would draw each Students should submit their sizes produced when d crystallisation one as part of a diagram. plan for approval before forming crystals quickly ... carrying it out. using a Bunsen burner, 2) Find some examples Evaluate the risks in a practical of pictures illustrating Equipment: Should include: and those produced by C0.6 filtration on the internet. conical flask (250 cm3), filter procedure and suggest suitable slow evaporation. To
C2a Mixtures C3.1 C3.2 Explain the differences between a pure substance and a mixture Interpret melting point data to distinguish between pure substances which have a sharp melting point and mixtures which melt over a range of temperatures 1) Begin by displaying a scanning tunnelling electron microscope image of some atoms as students come in. Challenge students to write one sentence indicating whether they think the image shows a pure substance or a mixture, and explaining how they can tell. 2) Ask students to match four materials (diamond, nitrogen, ice and gold) with their melting points in °C (3550, -210, 0, 1063). Students record the melting temperature of ice over time and compare this with the melting temperature of an mixture. Students should observe that the temperature of pure ice does not change as the ice is melting, but the temperature of the impure ice does. Equipment: 250 cm3 beaker, 5 ice cubes, 100 g salt (NaCl), thermometer or thermocouple (ideally with a lower range to −20°C), stop clock, mass balance Ensure that students fully understand the differences between pure substances and mixtures before moving on to look at their melting points. Discuss with the class what happens to the physical arrangement of particles during melting. A reasonable focus might be the ordering of particles and their separation. Digital: Pure substances and mixtures video C2b Filtration and crystalisation C3.3 C0.6 Explain the experimental techniques for separation of mixtures by ... c filtration d crystallisation ... Evaluate the risks in a practical procedure and suggest suitable 1) Hold up pieces of apparatus and ask what each one is. Ask students to explain or show how they would draw each one as part of a diagram. 2) Find some examples of pictures illustrating filtration on the internet. The aim of the investigation is to identify which of three samples of rock salt contains the largest quantity of salt. Students should submit their plan for approval before carrying it out. Equipment: Should include: conical flask (250 cm3), filter Demonstrate how to heat to dryness safely. Use the demonstration to compare the crystal sizes produced when forming crystals quickly using a Bunsen burner, and those produced by slow evaporation. To
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