KS3 Chemistry

1. KS3 Chemistry 9H Using Chemistry

2. Contents 9H Using Chemistry Chemical reactions Burning fuels New materials – everyday reactions New materials–industrial processes Summary activities

3. Chemical reactions everywhere! Chemical reactions take place around you and inside you all the time. How many reactions can you name? Burning,rusting,cooking and living all involve reactions. In a chemical reaction, reactants are changed into products and new materials are formed. Some chemical reactions are carried out to make new materials and some reactions are used to release energy. Are chemical reactions always useful?

4. Useful chemical reactions

5. Non-useful chemical reactions

6. What’s that reaction?

7. Contents 9H Using Chemistry Chemical reactions Burning fuels New materials – everyday reactions New materials–industrial processes Summary activities

8. Using combustion Combustion is the chemical reaction that takes place when a substance burns. The substance reacts with oxygen and energy is released as heat and light. Combustion is an important reaction as more than 90% of the world’s energy comes from burning fossil fuels like coal,natural gas and petrol. Where do fossil fuels come from and what other fuels are there?

9. Fire triangle

10. Formation of fossil fuels – coal

11. Formation of fossil fuels – oil and gas

12. What’s the best fuel?

13. Equations for combustion carbon dioxide carbon oxygen methane oxygen carbon dioxide water Combustion, as the reaction of substance with oxygen, is also called oxidation. The products of oxidation are oxides. • Coal is mostly carbon. The product of burning coal is a gas which turns limewater cloudy. What is the equation for burning coal? • Many fuels are hydrocarbons, which means they are made up of carbon and hydrogen. When hydrocarbons burn carbon dioxide and water (hydrogen oxide) are produced. What is the equation for burning the hydrocarbon methane?

14. Incomplete combustion carbon dioxide carbon oxygen carbon monoxide carbon oxygen A good supply of oxygen is needed for a fuel to burn completely and release as much energy as possible. When carbon reacts completely with oxygen, it is all turned into carbon dioxide. This is called complete combustion: If there is not enough oxygen, a fuel cannot burn completely and less energy is released. Some fuel is wasted. When carbon does not react completely with oxygen, the product is carbon monoxide, a colourless poisonous gas. This is called incomplete combustion:

15. Contents 9H Using Chemistry Chemical reactions Burning fuels New materials – everyday reactions New materials–industrial processes Summary activities

16. Rusting reaction Rusting is the reaction of iron with oxygen in the presence of water. Salt helps to speed up the rate of this reaction. Why does iron rust more quickly at the seaside?

17. Preventing rusting iron + oxygen iron oxide  Rusting is the reaction of iron with oxygen in the presence of water to form iron oxide (rust). Rusting is an ‘unhelpful’ chemical reaction. How do these measures help to prevent rusting? • Iron that is exposed to the weather is usually coated with a layer of paint. • New products that contain iron are often boxed with a small packet of drying agent. The paint prevents oxygen and water getting to the iron. The drying agent absorbs any water that may cause rusting.

18. Making bread and alcohol glucose + oxygen  carbon dioxide + water (+ energy) glucose  carbon dioxide + ethanol (+ energy) Yeast is a living organism which carries out chemical reactions that are used for making bread and alcohol. • Yeast uses oxygen from the air for aerobic respiration: The carbon dioxide gas produced in this reaction makes bread rise by filling it with bubbles. • Yeast can also carry out respiration without oxygen. This is anaerobic respiration, which is also calledfermentation: Fermentation is used to produce alcohol in beer and wine.

19. Ripening fruit The ripening of fruit is a complex collection of chemical reactions. Take apples as an example: • Starch is broken down into sugars increasing sweetness. • Acids are neutralized making the apples less sour. • Chlorophyll (green) changes to anthocyanin (red). • Pectin, a chemical which makes apples hard, is broken down and so makes the apples softer. Why do food producers and supermarkets need to know about the conditions and reactions involved in ripening fruit?

20. Ripening fruit The ripening of all fruit and vegetables involves similar chemical reactions. The speed of ripening is affected by the temperature and by the presence of a chemical called ethene. Food producers and supermarkets know the best conditions for slowing down or speeding up the ripening process so that fruit and vegetables do not go off too soon.

21. Cooking eggs Cooking involves chemical reactions – changes colour, taste and texture due toatoms in foodjoiningtogetherinnewways. Cooking an egg changes it texture from runny to firm: Eggs contain a protein called albumen.The protein molecules are long chains of amino acids folded into a ball shape. When eggs are heated, some of the protein atoms break apart and the molecules unfold. These molecules then join to other nearby protein molecules until they are all linked in a network.

22. Food spoilage Chemical reactions are not always useful. The changes that take place as food “spoils” are caused by chemical reactions. Apples turn brown when exposed to the air because they react with oxygen in the air. Knowing what causes this reaction can help to slow it down: • Placing sliced apples in water prevents browning because the apples are no longer exposed to air. • The chemical ascorbic acid (vitamin C), found in lemon juice, is also known to prevent the browning reaction.

23. Contents 9H Using Chemistry Chemical reactions Burning fuels New materials – everyday reactions New materials–industrial processes Summary activities

24. Making plastics from oil Plastics are very useful materials that are made by chemical reactions in factories. The starting materials for making plastics come from crude oil, which is found in the Earth’s crust. When crude oil is pumped out of the ground (or sea bed) it isa mixture of chemicals called hydrocarbons. Crude oil is separated into different hydrocarbons at an oil refinery using a process called fractional distillation.

25. Crude oil and fractional distillation boils at a lower temperature boils at a higher temperature Fractional distillationseparates crude oil based on the different boiling points of the hydrocarbon molecules. Small molecules boil at lower temperatures than bigger ones. The crude oil is heated and molecules of different sizes boil at different temperatures.These gases are collected separately and cooled, condensing to form different fractions. Some of the fractions obtained from crude oil, listed in order of increasing boiling point, are: fuel gas, petrol, naphtha, kerosine, dieseland bitumen. Which of these fractions has the biggest molecules?

26. Fractional distillation animation

27. Fractional distillation activity

28. Making plastics by polymerization The separated hydrocarbons obtained from the fractional distillation of crude oil have many uses. One of the main uses of the smaller hydrocarbon molecules obtained is to make plastics. Plastics consist of very long chains called polymers. The chemical reaction in which small molecules join together to make these very long polymer molecules is called polymerization.

29. Making plastics

30. Making metals by smelting Metals are very useful materials but many metals are found in rocks as compounds called ores. Iron, which is used to make steel, is found in the earth as iron ore. By heating the iron ore (mainly iron oxide) with carbon, the iron can be extracted. The carbon displaces the metal in a process called smelting. This process is the reverse of oxidation as the oxygen is taken away from the metal. It is called a reduction. In the reaction above, the iron oxide is reduced to iron.

31. Blast furnace animation

32. Electrolysis + aluminium oxide  aluminium oxygen Electrolysis is a chemical reaction that uses electricity to break up a compound and is another method for extracting a metal from its ore. For example, aluminium cannot be extracted by smelting and so electrolysis is used to aluminium metal from aluminium oxide. During electrolysis, the metal is always formed as a coating on the electrode that is connected to the negative electrode (the cathode.) This is why electrolysis is also used for the purification of copper and for electroplating other metals.

33. Electrolysis animation

34. Contents 9H Using Chemistry Chemical reactions Burning fuels New materials – everyday reactions New materials–industrial processes Summary activities

35. Glossary • combustion – The reaction of a substance with oxygen which releases heat and light energy. • electrolysis –A reaction that uses electricity to break up a compound and can be used for extracting metal. • fuel–A substance that is burnt to provide energy. • fractional distillation– The process used to separate a mixture, such as crude oil, into its components which have different boiling points. • hydrocarbons – Compounds that are made up of the elements carbon and hydrogen only. • polymers –Materials, such as plastics, that are made up of very long molecules. • smelting – Heating a metal ore with carbon to extract the pure metal.

36. Anagrams

37. Multiple-choice quiz