Mixing and separating chemistry

What is a mixture? combinations of two or more substances (start a glossary)

Mixtures in every day life…… ADD AN EXAMPLE TO YOUR GLOSSARY……

CEMENT

BOLTE BRIDGE-MELBOURNE

The Bolte Bridge is an eye-catching structure connecting freeways on the edge  of the city of Melbourne.  Over 50 000 tonnes of Goliath cement was used for the bridge. the bridge is supported by underwater foundations and over 3500 sections of  road wide enough for six lanes of traffic.  The cement is a mixture of pure substances, most naturally occurring,  that were mixed in just the right amounts to get the required balance of  physical properties.  The strength of the cement is vital, especially when you consider the weight it  supports during peak hour traffic.

OVER TO YOU! What is a mixture? Why is it important to mix the right ingredients  in the right amounts? Goliath cement is made of about seven different pure substances. What could they be? RECORD YOUR RESPONSES IN YOUR EXERCISE BOOKS

PURE SUBSTANCES something that is not mixed or combined with anything else (add to glossary)

Over to you! Here are some common household products with their ingredient labels. Identify which are pure substances and which are mixtures: DRAW UP A TABLE IN YOUR EXERCISE BOOKS

TABLE PURE SUBSTANCES MIXTURES

TABLE PURE SUBSTANCES MIXTURES BOTTLED WATER BEER COPPER SCOURER SOUP RUBBING ALCOHOL COLA DRINK CAUSTIC SODA ORANGE JUICE SALT PLASTIC WRAP?

MIXTURES SUMMARY Most of the substances we use every day are mixtures. Mixtures are combinations of two or more substances.  Most mixtures look like just one substance because the particles  they are made from are so small. There are so many possible combinations of mixtures, each with  different properties and purposes. For this reason, scientists have grouped mixtures according to  what they are made from and their behaviour.  Knowing the type of mixture helps us to work out ways that the  mixture can be separated into pure substances.

What are these MIXTURES made up of?

Types of mixtures Suspensions: cloudy liquids that contain insoluble particles (Add to Glossary) Dirty water is a type of mixture called a suspension.  Suspensions will often need to be shaken or stirred before use,  to spread the sediment through the liquid again.

A snow dome can be described as a suspension, with the ‘snow’ being suspended in the water for a short time  before it falls to the bottom of the dome to form  sediment.

Practical activity Dirty water What you need: soil, water, jar with screw top lid Put some soil and water in the jar to create a watery mixture. Screw the lid on tightly, then shake the jar.  Questions: What happens to the soil particles?  Does anything float on the water?  How can you explain the behaviour of this mixture?

Types of mixtures Colloids: types of mixtures that always looks cloudy because clumps of insoluble particles remain suspended throughout it-they don’t settle as sediment (Add to Glossary) When two or more substances are mixed, they don’t always separate out with time. Suspensions that don’t separate easily are referred  to as colloids.  These can be formed by a solid in a liquid but can also involve only liquids, only gases or even a solid suspended in a gas.  The word ‘colloid’ comes from the Greek word kolla which means  ‘glue’. You can think of a colloid as a substance being ‘stuck’—suspended in another substance. The benefit of colloids is that there is no need to mix them before using them. Hair gel and hand cream are examples of colloids.

colloids Fog is a colloid because it is air  containing suspended liquidparticles. Milk is a colloid because it contains many  substances suspended in  what is mainly  water.

Types of mixtures Emulsions: stable mixtures of two or more liquids, e.g. milk (Add to Glossary) An emulsion is a colloid of two or more liquids. Usually, one liquid is  the ‘base’ and the other is broken into tiny droplets spread throughout  the ‘base’ liquid. Milk is an example of an emulsion, with tiny droplets  of fats and oils spread throughout the base, which is water. In some cases, when mixtures like this are left to settle, the tiny droplets float above the base liquid. (This is different to what happens in a suspension, where the solid  particles tend to fall to the bottom of the liquid.) 

Types of mixtures Solutions: liquid made up of a solvent with a solute dissolved in it Solvent: any liquid that dissolves another substance or substances Solute: dissolves in a liquid (solvent) Copy out definitions into Glossary!

Solutions Sometimes water contains salts that affect its taste and behaviour. This type of water is an example of a mixture that doesn’t separate by  itself-a solution.  Spread evenly throughout solutions are particles so tiny that the solution  looks transparent. We say that sugar can dissolve in water to form a solution. A substance that is able to dissolve in a liquid is considered to be soluble, while one that cannot is insoluble.  The substance dissolving is called the solute, while the liquid into which it dissolves is called the solvent.  Sometimes it is necessary to help a solute to dissolve.  Warming is the most common way of making a solute dissolve faster.

More definitions Soluble: dissolves very easily in water e.g. Salt and Sugar Insoluble: does not dissolve

Working with solutions You have seen that a solution is a solute dissolved in a solvent.  Solutions can be compared in terms of their:  Concentration: how much solute is in the solvent. If just a little solute is  dissolved, the solution is described as dilute (low concentration).  If a lot of a solute is dissolved, then the solution is described as  concentrated (high concentration). It is only possible to dissolve a certain amount of a particular solute in a solvent. If no more solute can dissolve into a solution, the solution is  described as saturated-it cannot dissolve any more. We often work with solutions. By adding solutes to pure liquids, the  properties of the pure liquids may be changed.  An example is adding bath crystals to a bath to give a pleasant smell.

More definitions Dilute: Describing a solution with a small amount of solute (low concentration) Concentrated: Describing a solution with a large amount of solute (high concentration) Saturated: Describing a solution that can dissolve no more of a solute at a given temperature (cannot dissolve anymore)

Learning vocabulary Create your own word search -use the definitions of the words as clues -swap with a friend 2. Using your cue-cards test a partner