Unit 6M.2: Making pure substances from mixtures

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Marlene Matthews
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Crystals Science skills: Classifying Observing Predicting By the end of this unit

1 Unit 6M.2: Making pure substances from mixtures Making pure substances from mixtures Crystals Science skills: Classifying Observing Predicting By the end of this unit you should: Be able to suggest ways of separating dissolved solids from insoluble solids Know that crystallisation is a way of obtaining pure solids from solutions 90

6.11.3, 6.11.4 Materials You can make a UsolutionU by dissolving a solid like salt in water. The solution looks like pure water because the solid has broken down into tiny invisible particles.

2 6.11.3, Materials You can make a UsolutionU by dissolving a solid like salt in water. The solution looks like pure water because the solid has broken down into tiny invisible particles. To make the solid (UsoluteU) reappear, you can cause the UsolventU to UevaporateU, or turn into a gas. As the liquid disappears, the solid reappears because there is not enough liquid to dissolve it. You can get (water) the solvent again by condensation of the water vapour. 91

3 How can you separate a mixture of UinsolubleU solids from a liquid? UFiltrationU is used to separate a mixture of UinsolubleU solid and a liquid. The mixture is poured through a Ufilter paperu. Only the liquid passes through, and is called the UfiltrateU. We can use filter paper or a sieve to separate liquid from solid. 92

third full. Add a spoonful of salt, stir until all the salt has dissolved.

4 Activity: Getting a dissolved solid back. Material: Salt- Sugar Warm water A clear plastic tumbler A teaspoon Procedures: 1- Pour warm water into the tumbler until it is one third full. Add a spoonful of salt, stir until all the salt has dissolved. 2- Pour the salt solution into the saucer until there is a shallow pool, then put the saucer on a sunny windowsill or in some other warm, airy place. 3- Check the saucer twice a day for the next two or three days. What do you notice appearing on the saucer as the water gradually disappears? 93

Activity 2: Filtering through sand You will need A 500 ml plastic drink bottle Scissors Cotton wool Sand, gravel, pebbles Potting composite mixed with water Water Procedure 1-Cut the bottle in half.

5 Activity 2: Filtering through sand You will need A 500 ml plastic drink bottle Scissors Cotton wool Sand, gravel, pebbles Potting composite mixed with water Water Procedure 1-Cut the bottle in half. 2-Place the funneled end facing downwards into the base of the bottle. 3-Fill the funnel with cotton wool, pebbles, and gravel and sand, as shown, to make your filter. You might need to staple the funnel above the bottom. 4-Pour the composite mixed with water into the bottle and watch it drip through. 5-What color are the drips? How fast is the water passing through? 94

6 Activity: Getting dissolved solute back To obtain the solid from a mixture of sand and water and a salt solution. Materials Glass beaker Measuring cylinder Spatula Stirring rod Funnel Filter paper Conical flask Beaker Evaporating dish Hot plate 95

P P Materials Experiment 1: 3 1-Measure out 25cmP P of water into a 100 cmp 3 glass beaker. 2-Add 3 spatulas of sand to the water. 3-Stir the mixture until nothing else happens.

7 P P Materials Experiment 1: 3 1-Measure out 25cmP P of water into a 100 cmp 3 glass beaker. 2-Add 3 spatulas of sand to the water. 3-Stir the mixture until nothing else happens. 4-Set up the filter funnel, filter paper and conical flask. 5-Pour the sand and water mixture through the filter paper. 6-Write down exactly what happens Experiment 2: 3 1-Measure out 25cmP Pof water in a 100cmP 3 glass beaker. 2-Add 3 spatulas of salt to the water. 3-Stir the water until all the salt has dissolved. 4-Set up the filter funnel, filter paper and conical flask. 5-Pour the salt solution through the filter paper. 6-Write down exactly what happens

8 the the Materials Experiment 3: 1-Collect the salt solution formed during Experiment2. 2-Pour the salt solution into an evaporating dish. 3-Place the evaporating dish on a hot plate. 4-Write down exactly what happens. Conclusion : 1-Name the method that can be used to separate sand from a mixture of sand and water Name the method that can be used to separate salt from a salt solution In UExperiment 1U the solid remaining in the filter paper is called the. 4. In UExperiment 2U liquid that passes through the filter paper is called the. 5. In UExperiment 3U water that was in the evaporating dish goes into the. 97

9 Using the following equipment; draw a diagram to show how you would separate gravel from water, using filtration. You could also make this a flow chart with words. Scissors, mixing bowl, jug, funnel, paper towel, gravel 98

10 It is important when filtering not to over fill the filter paper. Examples of filtration in everyday life: 1- Water purification 2- Coffee making 3- Sewage Works purification 4- Vacuum cleaner 5- Drinking Water filter 99

11 Key idea We can separate solute from solution by evaporation and filtration Solids that will not dissolve are insoluble. Sometimes they are suspended in the solution (do not fall to the bottom). Key words Soluble Insoluble Suspended React Filtration Evaporation Purification Residue Project 1- Find a material that will make a good filter. Explain why you have chosen that material. How could you test it? List the equipment you would use. What would you be filtering? Choose some different mixtures. What would you measure to test the effectiveness of the filter? 2- Filtering is an important part of the process used to purify drinking water. Find out what material is used as a filter in water filtration plant. (You may be surprised!!) What is used in Qatar? What is used in other countries? 100

12 Key question 1-Filtration using the equipment shown can be used to separate which materials? A.A solution of copper sulfate and water. B. A solution of sodium chloride and water. C. A mixture of alcohol and water. D.A mixture of mud and water. E. A mixture of sand and sawdust. 2- Describe how you would separate the following mixtures A.A mixture of sand and iron filing : B. A mixture of sand and pebbles.: C. A mixture of sand and salt: Jamal put 10 cm3 of water and 3g of a different solid into each of four test-tubes. He shook each test-tube. The drawing shows the test-tubes after 10 minutes. a. Why can the sugar and salt no longer be seen in test- tubes A and C? A sugar B limestone C salt D sand b. If one of the solids was a mixture of salt and sand, what would Jamal see in the tube after 10 minutes? How would Jamal get from the tube (i) some pure sand and (ii) some pure salt? (i) (ii)

13 Materials Crystals A crystal: consists of matter that is formed from an ordered arrangement of atoms, molecules, or ions. Examples: 0Tquartz0T, 0Trock candy0t, 0Thalite0T Natural crystals: Natural crystals are dug out of the ground, where the earth's temperature and pressure cause them to form. Sugar Crystals Salt sugar USynthetic crystals Zincite Crystal Quartz Crystal 102

same substance have fundamentally the same shape. Crystals are a pure single substance.

14 Observe the pictures of crystals.what do you observe? The sides of crystals are flat and smooth; Crystals have a regular shape; All crystals of the same substance have fundamentally the same shape. Crystals are a pure single substance. Crystal can be cleaved easily (such as Iceland spar or mica). When crystals are cleaved the new faces are always parallel to the old ones. 103

Growing Crystals Do you want to grow great crystals? These are general instructions for growing crystals that you can use for most crystal recipes.

15 Growing Crystals Do you want to grow great crystals? These are general instructions for growing crystals that you can use for most crystal recipes. Obtain pure sample of a solute from a solution: Growing crystals You will need: Sugar Two clear plastic tumblers A Pencil - Cotton Paperclips Procedure: 1-Half fill a tumbler with warm water. 2-Stir in sugar until no more will dissolve, and then pour the clear solution into the other tumbler, leaving any undissolved sugar behind. 3- Use the pencil and cotton to suspend the paperclip in the solution. 104

16 Look at the paper clip every day for about a week and see what happens. My observation: Key idea Natural crystals are dug out of the ground, where the earth's temperature and pressure cause them to form. Crystals are structures that are formed from a regular repeated pattern of connected atoms or molecules. Key words Crystals Atoms Molecules Ions Natural crystals Synthetic crystals 105

17 Project Crystal gardens Drop a few coloured crystals into a 40% solution of sodium silicate ( water glass ) in a glass container. The crystals grow in vertical strands. The explanation involves osmosis and is beyond this grade. 106

Separating Mixtures. Name: Class:

Separating Mixtures. Name: Class: Separating Mixtures Name: Class: Directions: Match the words with the big ideas by writing the letter beside the idea. Use the same words in the short article below. Use key words and phrases from the