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8F Compounds and Mixtures

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1 8F Compounds and Mixtures
KS3 Chemistry 8F Compounds and Mixtures

2 8F Compounds and Mixtures
Contents 8F Compounds and Mixtures Comparing elements and compounds Compound names and formulae Word equations Mixtures Summary activities

3 Properties of elements and compounds
Why is it safe to put sodium chloride on fish and chips… …but not safe to use sodium and chlorine?

4 Atoms in elements and compounds
Elements are materials made up of one type of atom only. The element, hydrogen, exists as molecules. Each hydrogen molecule is made up of two hydrogen atoms joined together. H Compounds contain two or more different types of atom. The compound, water, exists as molecules. Each water molecule consists of two hydrogen atoms joined to one oxygen atom.

5 Element or compound?

6 Making a compound – water
A compound is made when atoms of different elements react and join together. For example, water is produced from the chemical reaction between hydrogen and oxygen. hydrogen oxygen water + H O + H Two hydrogen molecules react with one oxygen molecule to produce two molecules of water. Why does water have different properties to its elements?

7 Properties of a compound – carbon dioxide
A compound has different properties to the elements from which it is made because the atoms are joined differently. carbon oxygen carbon dioxide + Black solid used as fuel. Colourless gas in which many substances burn. Colourless gas used in fizzy drinks and fire extinguishers. + + O C

8 A compound is not a mixture
The atoms in a mixture of hydrogen gas and oxygen gas, which have not reacted with each other, look like this… The atoms in water, the compound made when hydrogen and oxygen react and their atoms become chemically joined to each other, look like this…

9 8F Compounds and Mixtures
Contents 8F Compounds and Mixtures Comparing elements and compounds Compound names and formulae Word equations Mixtures Summary activities

10 What is a mixture? A mixture contains two or more substances that are mixed together but have not reacted with each other. Sea water is a mixture of salts, water and other substances. A mixture is not the same as a compound: The proportions of the substances in a mixture are not fixed. The properties of a mixture are often an “average” of the properties of its ingredients (e.g. a mixture of a black and white powder is grey). 3. The substances in a mixture are just mixed, not chemically joined, and so it is usually quite easy to separate the ingredients (e.g. it is easy to get salt from sea water).

11 Element, compound or mixture?

12 Element, compound or mixture?

13 Separating immiscible liquids
Liquids that do not mix are described as immiscible. Examples of immiscible liquids are water with oil and water with petrol. On a small scale, immiscible liquids can be separated by simply removing the top layer using a pipette. water oil oil water

14 Separating miscible liquids
Liquids that do mix are described as miscible. Examples of miscible liquids are water with alcohol and petrol with kerosine. Miscible liquids can be separated by heating them to boiling. The components of the mixture have different boiling points and so will boil off at different temperatures. A condenser is used to recover the liquids as they boil off. This piece of apparatus is a tube that has cold water circulating around the outside. It cools down vapours and condenses them back to a liquid. Substances with low boiling points are collected first, while those with higher boiling points are collected later.

15 Distillation apparatus

16 Separating mixtures summary
A mixture containing something that DOES dissolve can be separated using __________ A mixture of liquids with different boiling points can be separated using _________ A mixture of different inks can be separated using _______ A mixture containing something that DOES NOT dissolve can be separated using _________ Distillation, chromatography, evaporation or filtration?

17 Separating mixtures Mixture Wanted Method glass and water glass filter
How can each mixture be separated? Mixture Wanted Method glass and water glass filter sea water salt evaporate sea water water distil cooking oil and water cooking oil pipette alcohol and water alcohol distil

18 Experiment to separate a mixture
Reggie has been given a mixture of salt, sand and water. He needs to separate these three substances but cannot remember how, so Reggie needs your help! Write an experimental plan for Reggie to follow so that he will end up with the sand, salt and water in separate containers. Start your plan with a list of the equipment that is needed for separating this mixture. Then write a step by step plan that is easy for Reggie or anyone else to follow.

19 True or false?

20 Multiple-choice quiz


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