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Boardworks KS3 Science 2008 Mixtures and Solutions

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1 Boardworks KS3 Science 2008 Mixtures and Solutions

2 Boardworks KS3 Science 2008 Mixtures and Solutions

3 Boardworks KS3 Science 2008 Mixtures and Solutions
What is a mixture? Boardworks KS3 Science 2008 Mixtures and Solutions A mixture contains two or more substances that are mixed together, but have not chemically bonded with each other. For example, seawater is a mixture of water, salt and other substances. A pure substance contains just one substance on its own. For example, table salt (sodium chloride) is a pure substance. Can you name some different mixtures, and pure substances, that you might find in your house?

4 What are the properties of a mixture?
Boardworks KS3 Science 2008 Mixtures and Solutions The substances in a mixture are not chemically bonded together. This means that it is usually quite easy to separate the substances (e.g. to get salt from seawater). The proportions in a mixture are not fixed (for example there might be lots of salt in seawater, or very little). The properties of a mixture are often an ‘average’ of the properties of the substances it is made from (e.g. a mixture of a red liquid and a blue liquid is a purple liquid). Photo credit: © 2008 Jupiterimages Corporation

5 Boardworks KS3 Science 2008 Mixtures and Solutions
Odd-one-out Boardworks KS3 Science 2008 Mixtures and Solutions Teacher notes Q2 – Vegetable oil is arguably a mixture too, rather than a pure substance, as it contains different types of triglycerides, but can be considered a pure substance in the context of this activity. Q3 - Sand grains are also arguably a mixture, as they could be from different types of rock, but again can be considered a pure substance in the context of this activity.

6 A mixture or a pure substance?
Boardworks KS3 Science 2008 Mixtures and Solutions

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What is a solution? Boardworks KS3 Science 2008 Mixtures and Solutions A solution is a special type of mixture that is made when one substance dissolves and mixes fully with another. For example, a cup of instant coffee is a solution. The solid that dissolves (e.g. coffee granules) is called the solute. The liquid that does the dissolving (e.g. hot water) is called the solvent. How many other solutions can you think of?

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Solvents and solutes Boardworks KS3 Science 2008 Mixtures and Solutions What is the solvent and what is the solute? black tea orange squash seawater wine fizzy drinks substance solvent solute water tea water flavours and sugar water salt water flavours/sugar/carbon dioxide water flavours and alcohol How many other examples of solutions can you think of?

10 Boardworks KS3 Science 2008 Mixtures and Solutions
Special solutions Boardworks KS3 Science 2008 Mixtures and Solutions Solutions do not have to be made from a solid and a liquid. Solutions can also be made by dissolving a gas into a solvent. For example, it is the dissolved oxygen in water that allows fish to breathe. Liquids can also be dissolved in other liquids, like alcohol in wine, and solids can even dissolve in other solids. For example, some alloys can be classified as solid solutions. Photo credit: Caroline Hawley

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Mixture or solution? Boardworks KS3 Science 2008 Mixtures and Solutions

12 Does everything dissolve?
Boardworks KS3 Science 2008 Mixtures and Solutions

13 What happens when something dissolves?
Boardworks KS3 Science 2008 Mixtures and Solutions Calcium carbonate is not soluble in water because the calcium carbonate and water particles are not able to mix. Copper sulfate is soluble in water because the copper sulfate and water particles are able to interact and mix together. water water copper sulfate calcium carbonate

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Dissolving in action? Boardworks KS3 Science 2008 Mixtures and Solutions

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Conservation of mass Boardworks KS3 Science 2008 Mixtures and Solutions If 10 g of salt is added to 50 g of pure water, what is the mass of the solution? + 50 g 10 g 60 g ? When the salt has dissolved, you can’t see it any more. How could you check that the salt is still there?

16 Boardworks KS3 Science 2008 Mixtures and Solutions
How much salt? Boardworks KS3 Science 2008 Mixtures and Solutions

17 Conservation of mass – extension
Boardworks KS3 Science 2008 Mixtures and Solutions If 10 g of salt is added to 50 g of seawater, what is the mass of the solution? + 50 g 10 g 60 g ? How much salt will be recovered if the mixture is separated by evaporation?

18 Does a solid keep dissolving?
Boardworks KS3 Science 2008 Mixtures and Solutions

19 How does temperature affect solubility?
Boardworks KS3 Science 2008 Mixtures and Solutions Does sugar dissolve in cold tea? It does, but not as much as in a cup of hot tea. The sugar is more soluble at higher temperatures. The amount of a solute that can dissolve at a given temperature is called its solubility. Mixtures and Solutions Worksheet 1 accompanies this slide (higher level activity, extra help may be needed for lower ability students). Photo credit: © 2008 Jupiterimages Corporation How does temperature affect the solubility of a substance? The solubility of a substance usually increases as the temperature increases.

20 Supersaturated solutions
Boardworks KS3 Science 2008 Mixtures and Solutions Supersaturated solutions are very saturated indeed. The solute will stay in solution until a ‘seed’ crystal is added, and then it will crystallise out of the solution very quickly. When it does this, it gives out heat energy. Supersaturated solutions are therefore used in heat packs. Teacher notes In heat packs, a mechanical disturbance, usually a spring-loaded button inside the pack, induces crystallisation.

21 Supersaturated solutions in action
Boardworks KS3 Science 2008 Mixtures and Solutions

22 Boardworks KS3 Science 2008 Mixtures and Solutions
Solubility of gases Boardworks KS3 Science 2008 Mixtures and Solutions Gases are unusual because their solubility decreases when the solvent gets hotter. Fish and other organisms that live in water survive by taking in oxygen that has dissolved in the water. Some scientists think that global warming is causing sea temperatures to rise. What effect do you think rising sea levels will have on the creatures that live in the sea? Photo credit: © 2008 Jupiterimages Corporation

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24 How could you separate these mixtures?
Boardworks KS3 Science 2008 Mixtures and Solutions Suggest some methods by which you could separate out these mixtures: chocolate buttons and raisins different coloured sweets pebbles and sand salt and sand mud and water oil and water gold and iron. Photo credit: © 2008 Jupiterimages Corporation

25 Separating an insoluble solid
Boardworks KS3 Science 2008 Mixtures and Solutions How could you separate an insoluble solid like sand from a mixture of sand and water? It is easy to separate an insoluble solid by filtering the mixture. The insoluble solid cannot pass through the filter paper but the water can. The sand that is trapped by the filter paper is called the residue. The water that passes through the filter paper is called the filtrate.

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Filtering apparatus Boardworks KS3 Science 2008 Mixtures and Solutions

27 Separating a soluble solid
Boardworks KS3 Science 2008 Mixtures and Solutions How could you separate a soluble solid, like salt, from a seawater solution? To separate a soluble solid from a solution, evaporation can be used. The solution is heated so that the water evaporates and leaves the dissolved solid behind.

28 Evaporation apparatus
Boardworks KS3 Science 2008 Mixtures and Solutions

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Salty water Boardworks KS3 Science 2008 Mixtures and Solutions Where does the salt around the Dead Sea come from?

30 Separating salt from seawater
Boardworks KS3 Science 2008 Mixtures and Solutions The Dead Sea is a salty lake, located between Jordan and Israel. The Dead Sea contains some of the saltiest water in the world! The Dead Sea is almost six times more salty than the ocean, so nothing is able to live in it and that’s why it is called ‘dead’. Photo credit: © 2008 Jupiterimages Corporation The heat of the Sun evaporates the water from the Dead Sea, and the salt that is left behind is collected in salt beds.

31 Separating salt from rock salt
Boardworks KS3 Science 2008 Mixtures and Solutions We also get salt from rocks called ‘rock salt’. Rock salt is a mixture of salt with sand and bits of rock. Rock salt was traditionally extracted by hand from underground mines; a very dangerous process. Today, rock salt is mined using earth-moving equipment before being purified. Mixtures and Solutions Worksheet 2 accompanies this slide. Photo credit: © 2008 Jupiterimages Corporation How could you use dissolving, filtering and evaporation to separate the salt from rock salt?

32 Separating immiscible liquids
Boardworks KS3 Science 2008 Mixtures and Solutions Liquids that do not mix together are described as immiscible. Can you think of any examples of immiscible liquids? On a small scale, immiscible liquids can be separated by simply removing the top layer using a pipette. + oil water In laboratories, chemists use a separating funnel to separate immiscible layers.

33 Separating miscible liquids
Boardworks KS3 Science 2008 Mixtures and Solutions Liquids that do mix together are described as miscible. An example of this is water and alcohol – these two liquids mix together easily. Can you think of any more examples of miscible liquids? + How could you separate a mixture of miscible liquids?

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Distillation Boardworks KS3 Science 2008 Mixtures and Solutions The technique used to separate a liquid from a mixture is called distillation. Distillation has three steps: evaporation condensation collection The solution is heated so that the liquid evaporates and is turned into a gas. Everything else is left behind. Photo credit: David Ritter The gas cools in the condenser and turns back into a liquid, which can then be collected. Could distillation be used to make seawater safe to drink?

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Distillation Boardworks KS3 Science 2008 Mixtures and Solutions

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Chromatography Boardworks KS3 Science 2008 Mixtures and Solutions Chromatography means colour-writing. Chromatography is used to separate mixtures of coloured or non-coloured substances that are soluble in the same solvent. A spot of the mixture is placed on some filter paper. In method A, the solvent is soaked up the paper. In method B, the solvent is slowly dripped onto the paper.

37 Chromatography experiment
Boardworks KS3 Science 2008 Mixtures and Solutions

38 Identifying dyes in a mixture
Boardworks KS3 Science 2008 Mixtures and Solutions Dots of single dyes are placed alongside a dot of unknown mixture. Teacher notes The mixture contains dyes 3 and 5. The solvent washes up the paper, and then the pattern of the dyes in the mixture can be compared with the single dyes. Which dyes does the mixture contain?

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Which dyes? Boardworks KS3 Science 2008 Mixtures and Solutions

40 Uses of chromatography
Boardworks KS3 Science 2008 Mixtures and Solutions How many uses of chromatography can you spot? Teacher notes This illustration contains several uses of chromatography, including: Counterfeiting Chromatography is used for detecting forgeries by matching inks from forged money with ink from suspects’ printing machines. DNA fingerprinting DNA fingerprinting is used identify the unique genetic makeup of an individual. This is done using a version of chromatography called electrophoresis, which involves separating out DNA fragments according to their size. Forensics Column chromatography is often used to separate the compounds in a mixture, such as drugs from blood, or pollutants from water. Drug testing Gas chromatography machines are used to identify the chemical make-up of unknown substances. During gas chromatography different amounts of different molecules will ‘stick’ to the column, so it can be used to find the masses (and therefore chemical structure and identity) of the compounds.

41 Which separation technique?
Boardworks KS3 Science 2008 Mixtures and Solutions

42 Boardworks KS3 Science 2008 Mixtures and Solutions
Separating mixtures Boardworks KS3 Science 2008 Mixtures and Solutions

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44 Boardworks KS3 Science 2008 Mixtures and Solutions
Glossary Boardworks KS3 Science 2008 Mixtures and Solutions Glossary chromatography – A method used to separate two or more soluble substances in a mixture dissolving – The mixing of a solid with a liquid to make a solution. distillation – A method used to separate a liquid from a mixture evaporation – A method used to separate a soluble solid from a liquid filtration – A method used to separate an insoluble solid from a liquid mixture – Two or more substances that are mixed together but are not chemically joined. saturated – A solution containing the maximum amount of solute that it can hold. soluble – A substance that can dissolve in a solvent. solubility – A measure of how much solute can dissolve in a solvent at a given temperature. solute – A Solid that dissolves in a solvent to make a solution. solution – A mixture made when a solute dissolves in a solvent. solvent – A liquid in which a solid dissolves to make a solution.

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Anagrams Boardworks KS3 Science 2008 Mixtures and Solutions

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Multiple-choice quiz Boardworks KS3 Science 2008 Mixtures and Solutions


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