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At the end of this unit you should:

At the end of this unit you should: 1 . Be able to explain how to separate the components of mixtures. 2. Know how to separate an insoluble solute from a solvent, by several different methods. 3. Know how to separate a soluble solute from a solvent, by several different methods.

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At the end of this unit you should:

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  1. At the end of this unit you should: 1. Be able to explain how to separate the components of mixtures. 2. Know how to separate an insoluble solute from a solvent, by several different methods. 3. Know how to separate a soluble solute from a solvent, by several different methods. 4. Be able to separate two miscible liquids. 5. Understand the importance of a variety of separation techniques, in science and industry.

  2. adsorption boiling point capillary action chromatography chromatography paper distillate distillation evaporation filter filter funnel filter paper filtrate filtration flocculation impure insoluble Liebig condenser miscible permeable pure residue sedimentation separation techniques settling sieve

  3. Mixture: Two or more substances mingled together but not chemically combined. Pure: When a substance or mixture is not contaminated or polluted by an unwanted substance. Impure: When a substance or mixture has been contaminated or polluted by another unwanted substance.

  4. LIGHTBULB QUESTION If the sample is impure it could affect the accuracy of an analytical test. Air is collected from unpolluted airspaces and a mean figure for each gas is calculated.

  5. (a) Table 06.03.01 lists a variety of mixtures. Copy the table and complete it by ticking a box in either the ‘pure’ or ‘impure’ column for each mixture.

  6. (b) Can you think of two additional mixtures you use in your daily life? Air, breakfast cereal and milk.

  7. LIGHTBULB QUESTION Tea-bags are an example of filters in everyday use that you might not have considered. The tea particles inside the tea-bag diffuse into the water. Weblinks Showing diffusion of tea through hot water using a tea-bag: https://www.youtube.com/watch?v=sX1wx3UW6dw Showing how different tea strainers can be used: http://coffeetea.about.com/video/How-to-Use-Tea-Strainers.html

  8. Filtration: Separation of an insoluble solid from a liquid or gas. Filtrate: The liquid that is collected after passing through the filter. Residue: The insoluble solid left in the filter after filtration.

  9. Investigation 06.03.01: Testing how to filter a mixture Equipment: A filter funnel, filter paper, a soil and water mixture, two 300 ml beakers, retort stand (with clamp or ring clamp)

  10. Investigation 06.03.01: Testing how to filter a mixture Instructions: 1. A large beaker of a water–soil mixture should be made up for students to access as they need. 2. A simple-fold filter paper should be used. http://www.wikihow.com/Make-a-Water-Filter 3. The mixture should be passed through the filter until a clear filtrate is collected.

  11. A filter funnel is not an important piece of equipment in this investigation. Do you agree or disagree? Justify your answer. • When filtering into a narrow necked vessel, a filter funnel is essential. But if the neck of the collecting container was much wider and a material other than paper was used, a filter funnel would not be essential.

  12. 2. Are all types of paper the same? Suggest how you might prove this. • No. Carrying out filtrations of the same mixture using filters made from the different papers would prove that the papers had different filtration properties.

  13. LIGHTBULB QUESTION For example: water pumps, washing machines, dishwashers, tumble driers, power-hose washers, in-built or jug water filters.

  14. Investigation 06.03.02: Testing the best way to filter an insoluble solid Instructions: The simple paper fold (cone filter) can be done using Method 1 from the diagram or by following this link: https://www.youtube.com/watch?v=or6ex5toLVg

  15. Investigation 06.03.02: Testing the best way to filter an insoluble solid Instructions: Fluted filter paper folding can be done using Method 2 from the diagram or by following this link: https://www.youtube.com/watch?v=ykmTxRpRRCw

  16. Investigation 06.03.02: Testing the best way to filter an insoluble solid Equipment: Conical flask, filter funnel, filter paper, 200cm3 clay-water mixture, two 100cm3 beakers, spatula, retort stand (with clamp or ring clamp), stop clock. Instructions: 1. Pass a fixed volume of water through each filter fold type several times. The volume does not have to be measured as the markings on the side of the 100 ml beakers are sufficient once 20–25 ml is used. 2. As each group will have 200 ml of stock mixture, this will need to be stirred regularly to prevent settling.

  17. 1. How did you set up the equipment for this investigation? Justify your answer. • Because two ways of folding filter paper are being tested, the equipment has to be set up the same for each run of the tests. If this is done, the only difference will be the filter paper fold type, so a comparison can then be made fairly.

  18. 2. You used additional equipment in this investigation compared to the previous one. Did the extra equipment in this investigation improve how you carried it out? • Explain your answer. • Yes, there was an improvement, as the extra equipment allowed comparison testing of the two fold types to happen fairly.

  19. 3. Was there a difference between how the two filters worked? How can you prove this? • Yes. The amount of time that the mixture took to be filtered shows a difference between the two fold types.

  20. Permeable Having pores that allow gases or liquids to pass through a membrane.

  21. DEMONSTRATION Equipment: Two 100 ml beakers, deionised/distilled water, 0.1 M potassium permanganate solution, food dye/fountain pen ink/universal indicator, two disposable Pasteur pipettes, two non-waxed cup-cake liners. Demonstration 06.03.01 – Showing selective permeability

  22. DEMONSTRATION Instructions: Each of the beakers should be filled to near the brim with water and a cup-cake holder placed in each. 2. Some potassium permanganate should be added to one cup-cake holder. 3. An equal amount of another coloured solution should be added to the second cup-cake holder. Demonstration 06.03.01 – Showing selective permeability

  23. 1. Non-waxed cup-cake liners must be used for this investigation – why? • Similar to the upper surface of plant leaves, the wax coating will form an impermeable barrier, so will not let any particles/solutes pass through.

  24. 2. Repeat this demonstration at home using either ink or food dye. Are the results different from the first version of this demonstration? Explain your answer. Depending on the particle size of the dye used, the DIY test may either be faster of slower.

  25. Settling: Allowing undissolved solids in a solution to sink to the bottom of a container. Flocculation: Using chemicals to cause solids to clump together and sink.

  26. (a) Fish absorb oxygen directly from the water they swim in, but how can they do this without absorbing lots of water and becoming bloated? The membranes of fish gills only allow oxygen molecules to pass, which are a different size and shape to water molecules.

  27. (b) The top surface of a plant leaf has a waxy coating to help it survive in changeable weather. How do you think this waxy coat helps plants? Waxy coatings on plants are impermeable to water. This means that in strong sunshine or heat the water cannot evaporate through the wax layer on the outside of the leaf. The top side of plain leaves are normally waxy to avoid dehydration from the heat of the sun, but the bottom surface has pores to allow gases to pass in and out of the leaves.

  28. Distillation: The process in which a liquid is boiled and its vapour is condensed and collected. Miscible: How two liquids mix evenly with each other. Evaporation: The changing of a liquid to a gas when the surface of the liquid is heated.

  29. Residue: The solute that is less after a solvent has been removed from a solution by distillation or evaporation. Distillate: The liquid that has been condensed from a vapour and is collected from the condenser.

  30. Investigation 06.03.03: Comparing methods of evaporation Equipment: A Bunsen burner or hotplate, 100 cm3 salt water (or copper sulfate) solution, a tripod, a wire gauze, 500 ml beaker and an evaporating dish.

  31. Instructions: 1. The class group is split in two with one group taking Method 1 and the other Method 2. 2. Each group receives an equal measure of coloured saltwater (food dye can be added to a salt solution without affecting the outcome, to allow the salt to be more easily seen when evaporated). 3. A kettle has been boiled to provide hot water for the water baths in Method 2. 4. When the solutions in the evaporating dishes have greatly reduced and are forming a light foam, the Bunsen burner should be switched off. The residual heat of the evaporation dish is sufficient at this point. This also prevents ‘spitting’ of salt particles.

  32. 1. Which method would you prefer to use – explain why. For speed and convenience, Method 1 would be better but the spitting of salt is a drawback and if left unattended the evaporation dish may become too hot and crack. Method 2 also has the problem of a significant amount of boiling water spilling if an accident occurs.

  33. 2. What safety precautions did you need to take for these methods? Justify why one method is safer than the other. • With both methods the evaporation has to be monitored so that the Bunsen can be turned off at the right time. But Method 2 requires boiling water, so disassembling requires more care in handling. In general, the apparatus with the least number of parts is easier and therefore safer to use and disassemble.

  34. 3. Can you think of another method of evaporation? • List the advantages and disadvantages of this method. • Leaving the solution out to evaporate has the disadvantage of taking a lot of time but has the following advantages: • • Little equipment needed • • No heat needed • • Once placed in a safe position does not need constant monitoring.

  35. Investigation 06.03.04: Separating miscible liquids Equipment: Liebig condenser, quick-fit connections, a round-bottomed flask, a beaker, a Bunsen burner, a tripod, some wire gauze and a 100 cm3alcohol–water mixture.

  36. Instructions: 1. The quick-fit apparatus should be set up as shown in the diagram (Refer to your instructions for this investigation.) 2. Joint clips should be used as indicated. 3. The round-bottomed flask should be mounted in a clamp (by the neck) about 1.5 cm above the wire gauze. 4. The still-head can then be attached. 5. The Liebig condenser should be clamped at its centre in a second retort stand. It should then be inclined to match the still-head joint angle, and then slid into place.

  37. Instructions: 6. The cap of the thermometer adaptor should be loosened slightly and the thermometer threaded through (twisted gently, like turning a screwdriver) until there is sufficient length for the thermometer bulb to sit just below the still-head side arm. The cap can then be tightened. 7. The receiver adaptor can then be attached to the bottom of the Liebig condenser, and a small beaker placed underneath to collect the distillate. 8. The hose from the lower Liebig condenser side pipe should be attached to a running tap, with the other hose acting as a drain. The hoses should be arranged in this order to prevent heat shock at the top of the condenser inner tube causing cracking or shattering.

  38. Instructions: 9. To prevent spillage, the alcohol mix is added using a thistle funnel, so that the mix does not run down the still-head side arm into the condenser. Adding the alcohol mix at this point removes potential for spills during assembly and safely controls the movement of the alcohol mix around the room. 10. The size of round-bottom flask will vary depending on kit manufacture and model; however, no more than approximately half the volume of the flask should be filled with the alcohol mix. 11. If a pear-shaped flask is being used, anti-bumping chips (or small marble chips) should be used as this shape of flask tends to heat the liquid mix unevenly and can cause vigorous bubbling. This can cause the mix to overflow into the condenser if not caught in time.

  39. Instructions: 12. The Bunsen flame should be a mid-range blue so that there is a steady simmering of the mix. The mix should be monitored constantly so that the flame can be adjusted appropriately. 13. When the distillation is complete, heat gloves should be used to dismantle the apparatus carefully. 14. The distillate must then be poured into a large disposal beaker under supervision. Water and soap can be added to the waste alcohol before washing down a foul drain and flushing with plenty of water.

  40. 1. What other piece of equipment do you need in order to set up the distillation? • Two retort stands so the equipment can be mounted and jointed in a safe and stable way. • 2. Why does the outer tube of the Liebig condenser need water • flowing through it? • So the inner tube is cool enough to allow condensation of the vapour to happen. • 3. Can you suggest why the flow of water should only be set up as in the diagram? • To prevent heat shock and cracking at the top of the Liebig condenser.

  41. 4. How did you know when to stop heating the mixture? • Explain how this is a reliable way to decide when to stop. • The alcohol boils at 78.5oC so by watching the thermometer the heat can be reduced or increased as needed. This is reliable as it depends on a measureable quantity.

  42. 5. Was the distillate pure alcohol? Give reasons for your answer. • It is unlikely that the distillate is completely pure as some impurities could have been carried by the vapour. The alcohol would have to be distilled several times to ensure purity.

  43. (a) What is the function of the Liebig condenser? To condense vaporised liquids in a way that allows them to be collected.

  44. (b) Is it possible to use the Liebig condenser without water running through it? Explain why. It is possible but little or no condensation would happen before the inner tube becomes too warm and vapour would escape out of the condenser.

  45. (c) Do you agree that a Liebig condenser should not be used to separate a dissolved solid from a solvent? Why? Evaporation is an easier and simpler method to use and the residue does not stick to the inside of a flask with a narrow neck, which would make it difficult to clean. But if the distillate and not the salt is wanted, then it would be the better method.

  46. Adsorption: The attraction of a substance to the surface layer of another substance. Capillary Action: The process of water particles sticking to each other and to the walls of narrow tubes, which causes water to rise in the tubes. Chromatography: The separation of dissolved substances in a solution by their attraction to the solvent.

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