Good Science Victorian Curriculum Year 7

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CHEMICAL SCIENCES 5.6 SEPARATION TECHNIQUES: EVAPORATION AND DISTILLATION At the end of this lesson I will be able to describe the processes of evaporation and distillation and suggest when these techniques should be used. KEY TERMS condenser a glass tube cooled by water that cools a gas to become a liquid crystallisation separation of a solution by evaporating the solvent, leaving behind solute crystals distillation using heating to separate liquids with different boiling points LITERACY LINK SPEAKING Explain to a partner how the process of evaporation works, and describe a situation when it would be used. Then swap roles, with your partner explaining distillation. 1 Australia is a country that experiences frequent droughts and water shortages. The country is surrounded by oceans; however, salt water cannot be used by land-dwelling living things. One way to use this resource is to separate the salt from the water. Desalination is a process that uses separation techniques such as evaporation, distillation and crystallisation to purify salt water. Solids can be evaporated and crystallised out of liquids To separate a solid such as salt from water, without keeping the liquid, we can heat the mixture until the water boils and leaves the mixture as a gas. This method is called evaporation. Crystallisation – the formation of crystals of the substance that was dissolved in the liquid – will start to happen when most of the liquid has evaporated. Smaller crystals form if the liquid evaporates quickly, and larger crystals form if it evaporates slowly. What is the difference between evaporation and crystallisation? Figure 5.11 In the laboratory, a solution of salt water can be heated until the water evaporates and the solid salt begins to crystallise. Water evaporates from salt water solution Salt crystals NUMERACY LINK CALCULATION In a laboratory distillation, 45 g salt is separated per 100 mL of water. If you begin the investigation with 500 mL of water, how much salt do you predict you will have at the end? Figure 5.12 Salt evaporation ponds are shallow artificial 'ponds' designed to extract salt from sea water. Natural salt ponds are geological formations that occur naturally when water evaporates and leaves behind a salt flat. 78 GOOD SCIENCE VICTORIAN CURRICULUM 7
CHAPTER 5: MIXTURES 2 Distillation can be used to purify water Distillation can be used to separate pure water from salt. First, the salt water is heated in a glass flask. The water evaporates and the water vapour is captured. It is then cooled in a tube called a condenser, which has cool water flowing around it. This changes the gas to a liquid. This change is called condensation. The condensed liquid is collected in a different beaker, while the salt crystals remain in the flask. Distillation can also be used to separate two liquids, such as water and alcohol. The physical property that allows these substances to be separated is boiling point (which is different for every substance). What is distillation? INVESTIGATION 5.6A Evaporating a solution KEY SKILL Identifying limitations to the method and suggesting improvements Go to page 159 INVESTIGATION 5.6B Growing crystals KEY SKILL Identifying the variables and formulating a hypothesis Go to page 160 INVESTIGATION 5.6C Distillation (Teacher demonstration) Go to page 161 Figure 5.13 In a laboratory distillation set-up, a Bunsen burner heats a mixture and evaporates the liquid. This gas changes to a liquid in the condenser. Solution Thermometer water outlet Condenser Cooling water Condensed liquid (this is called the 'distillate') CHECKPOINT 5.6 1 Evaporation and crystallisation are related. Suggest how. 2 Give an example of a mixture that can be separated by evaporation and crystallisation. 3 Describe a situation in which you could separate something using distillation. 4 Identify the physical property of a substance that is used to separate mixtures in distillation. 5 Suggest how you would go about creating large crystals using crystallisation. CONTEMPORARY ISSUES 6 Research how a desalination plant uses the process of reverse osmosis to purify water. Use labelled diagrams to present your findings. Bunsen burner Water inlet Flask SUCCESS CRITERIA I can describe the difference between evaporation, crystallisation and distillation. I can give examples of situations in which each technique could be used to separate mixtures. 79
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MAKE EVERY LESSON A GOOD LESSON
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Chapter 5 Mixtures . . . . . . . .
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VICTORIAN CURRICULUM SCIENCE LEVELS
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INVESTIGATIONS KEY SKILLS Writing a
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INVESTIGATIONS METHOD 1 Copy the re
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INVESTIGATIONS RESULTS 30 min Level
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INVESTIGATIONS Investigation 5.6A E
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INVESTIGATIONS Investigation 5.7B S
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INVESTIGATIONS 30 min Level 2 TO MO
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INVESTIGATIONS Investigation 7.3A D
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INVESTIGATIONS METHOD 1 Copy the re
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fractional distillation a method th
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INDEX Aboriginal and Torres Strait
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photosynthesis 30, 31, 36, 42, 109
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Good Science Victorian Curriculum Year 7

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