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© Boardworks Ltd 2005 1 of 32 KS4 Chemistry Useful Air.

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1 © Boardworks Ltd of 32 KS4 Chemistry Useful Air

2 © Boardworks Ltd of 32 Useful Air Manufacture of fertilizer Fertilizers and the environment What is air? Summary activities Manufacture of ammonia Contents

3 © Boardworks Ltd of 32 Around 78% of the air is nitrogen. About 21% is oxygen. The remaining 1% is mostly argon (0.93%), with carbon dioxide (0.04%) and varying amounts of water vapour. What is air made of?

4 © Boardworks Ltd of 32 Separating the gases in air

5 © Boardworks Ltd of 32 When air is distilled: 1.Which gas will boil first? 2.Which gas will there be most of? 3.Which gas will there be least of? nitrogen argon Here are the boiling points of the three main gases in air: nitrogen: – 196ºC oxygen: –183ºC argon: –186ºC Separating gases

6 © Boardworks Ltd of 32 Useful Air Manufacture of fertilizer Fertilizers and the environment What is air? Summary activities Manufacture of ammonia Contents

7 © Boardworks Ltd of 32 Nitrogen is a very unreactive gas which tends to react slowly if at all. Changing the element nitrogen into compounds that plants can absorb involves reacting the nitrogen with hydrogen to form ammonia. nitrogen + hydrogen  ammonia N 2 + 3H 2  2NH 3 Nitrogen and ammonia  

8 © Boardworks Ltd of 32 Can you suggest ways of speeding up the reaction of nitrogen with hydrogen? 1.Use a catalyst 2.Use a high temperature 3.Compress the gases The actual conditions used are: 1.An iron catalyst 2.A temperature of 450 o C 3.A pressure of 200 atmospheres The Haber process (1)

9 © Boardworks Ltd of 32 Even under these conditions only part of the nitrogen and hydrogen react to form ammonia. If the temperature is raised too high the ammonia increasingly decomposes back into the reactants. The reaction is said to be reversible. nitrogen + hydrogen  ammonia Getting the best rate of conversion into ammonia involves a very careful choice of reaction conditions. The Haber process (2) 

10 © Boardworks Ltd of 32 The Haber process gives a mixture of reactants and products. Here are the boiling points of the substances involved. 1.Which one most easily turns into a liquid? 2.How might ammonia be separated from unreacted nitrogen & hydrogen? The Haber process nitrogen hydrogen ammonia °C

11 © Boardworks Ltd of 32 The Haber process

12 © Boardworks Ltd of 32 The Haber process

13 © Boardworks Ltd of 32 Complete the process

14 © Boardworks Ltd of 32 Useful Air Manufacture of fertilizer Fertilizers and the environment What is air? Summary activities Manufacture of ammonia Contents

15 © Boardworks Ltd of 32 The majority of ammonia is used for the manufacture of fertilizers, but there are other uses. Uses of ammonia

16 © Boardworks Ltd of 32 Ammonia is sometimes pumped directly into the soil as a fertiliser but because it is a gas much of it may escape. More usually some of the ammonia is reacted with oxygen to form nitric acid NH 3 + 2O 2  HNO 3 + H 2 O This nitric acid is then reacted with more ammonia to give solid ammonium nitrate HNO 3 + NH 3  NH 4 NO 3 Ammonia and fertilizers

17 © Boardworks Ltd of 32 Manufacture of ammonium nitrate

18 © Boardworks Ltd of 32 Manufacture of ammonium nitrate

19 © Boardworks Ltd of 32 Complete the process

20 © Boardworks Ltd of 32 Useful Air Manufacture of fertilizer Fertilizers and the environment What is air? Summary activities Manufacture of ammonia Contents

21 © Boardworks Ltd of 32 Ammonia and fertilizer What are the advantages and disadvantages of different types of fertilizer?

22 © Boardworks Ltd of 32 In a group of 3 or 4 write the words ‘The effects of fertilizer’ in the middle of a piece of A3 paper. Around the outside write down all of the effects – good and bad - that fertilizers can have on the environment. The effects of fertilizer

23 © Boardworks Ltd of 32 Fertilizers They have made naturally infertile soils suitable for agriculture. This has been significant in poorer parts of the world. They eliminate the need to allow fields to lie fallow and for crop rotation. This enhances the productivity of the land. They increase the yield of the crops produced. This has allowed more land to be set aside for nature conservation and recreation. Advantages of fertilizers

24 © Boardworks Ltd of 32 Fertilizers applied to farm land Too much used, at the wrong time of year, during wet weather, if Excessive growth of aquatic plants. The bacteria which live on dead plants thrive and use up the oxygen in the water. The lack of oxygen causes death of fish. This is called eutrophication. Harm to infants - called ‘blue baby’ syndrome Washed into rivers and lakes causes excess Contaminates underground drinking water supplies causes Disadvantages of fertilizers

25 © Boardworks Ltd of 32 Growmore is an NPK fertiliser (7-7-7) containing about 7% nitrogen, 7% phosphorous and 7% potassium. Growmore

26 © Boardworks Ltd of 32 Potassium (K) - speeds up seed growth and improves resistance to disease. Nitrogen (N) - needed for proteins in leaves and stalks. Phosphorous (P) - speeds up growth of roots and helps fruit to ripen. NPK fertilizers

27 © Boardworks Ltd of 32 Farmer Giles has been accused of raising nitrate levels in local water by using too much fertilizer. Here are some suggestions from other locals. Are they good or bad? Split the fertilizer over 3 applications instead of just one. Use a more soluble fertilizer so that it gets into the plants more easily. Check the weather forecast and avoid applying fertilizer before rain is due. Grow a quick crop of legumes instead of using a nitrogen-containing fertilizer. Use fertilizer with larger particle size. A problem for Farmer Giles

28 © Boardworks Ltd of 32 Answers 1.Three applications instead of just one – good Plants get time to take in each application. 2.More soluble fertilizer – bad It will dissolve in rain and wash into local drains. 3.Avoid applying it before rain is due – good This means it won’t dissolve in the rain and wash into drains. 4.Grow a quick crop of legumes – good But depends on timings of crops, etc. 5.Use fertilizer with larger particle size – good Using the same amount of fertilizer with larger particles is likely to lead to a slower dissolving into the ground, giving plants more time to absorb it.

29 © Boardworks Ltd of 32 Useful Air Manufacture of fertilizer Fertilizers and the environment What is air? Summary activities Manufacture of ammonia Contents

30 © Boardworks Ltd of 32 Glossary air – A mixture of gases containing mainly nitrogen and oxygen, but with small amounts of other gases. ammonia – A gas used in the manufacture of fertilizer and nitric acid. catalyst – A substance that changes the rate of a reaction without being used up. eutrophication – Excess plant growth in water leading to reduced oxygen levels, caused by increased nutrient levels. fertilizer – A substance added to soil to increase its productivity. Haber process – The industrial process used to manufacture ammonia from nitrogen and hydrogen. NPK – A type of fertilizer containing nitrogen, phosphorous and potassium.

31 © Boardworks Ltd of 32 Anagrams

32 © Boardworks Ltd of 32 Multiple-choice quiz


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