AMMONIA AND FERTILISERS What is a reversible reaction? How do we make fertilisers? What are the benefits and drawbacks of using fertilisers? Name ____________________________ Class __________ Date __________ Teacher ____________________________ CHEM - ADDITIONAL BOOKLET 5 1 AMMONIA AND FERTILISERS Tick You should: Know that ammonia is made from atmospheric nitrogen by the reversible reaction Interpret given data to show how the yield of product depends upon the conditions used in the manufacture of ammonia Know how nitrogenous fertilisers such as ammonium sulphate and ammonium nitrate are obtained by neutralising ammonia solution (ammonium hydroxide) with sulphuric acid or nitric acid respectively. Evaluate the advantages and disadvantages of using nitrogenous fertilisers for individuals, communities and the environment. Identify the presence of an ammonium salt by reaction with sodium hydroxide solution to produce ammonia gas Identify the alkaline gas ammonia by its action on damp red litmus paper 2 NITROGEN CHEMISTRY INTRODUCTION ABOUT NITROGEN Nitrogen was discovered by chemist and physician Daniel Rutherford in 1772. Nitrogen compounds are found in foods, organic materials, fertilisers, poisons, and explosives. Nitrogen, as a gas is colourless, odorless, and generally considered an inert element. As a liquid (boiling point = - 195.8oC), it is also colorless and odorless, and is similar in appearance to water. Watch the following clip showing a banana and apple being dipped into liquid nitrogen. Click on picture. Google Image Result for http://www.ilpi.com/genchem/demo/liquidnitrogen/nitrogenintro.jpg 79% of the air around us is nitrogen. Living things need nitrogen to make proteins, but they cannot get it directly from the air because nitrogen gas is too stable to react inside an organism to make new compounds. OBTAINING NITROGEN FROM THE AIR- NITROGEN FIXATION Nitrogen must be changed into a more reactive form to allow plants and animals to use it. Plants can take up and use nitrogen when it is in the form of: Nitrates Ammonium salts. Changing nitrogen into a more reactive substance is called nitrogen fixation. 3 Nitrogen fixation happens in three main ways: 1. The energy in a lightening bolt can split the nitrogen molecule in the air allowing each nitrogen atom to react with oxygen to form nitrogen oxides. These oxides are washed to the ground by the rain where they form nitrates. 2. The Haber Process is used by industry to produce ammonia from nitrogen. Ammonia is used to make fertiliser for farmers to feed their crops. 3. Nitrogen-fixing bacteria found in the soil and in the root nodules of leguminous plants fix nitrogen into a usable form. Other ways in which nitrogen compounds are returned to the soil are by excretion and egestion from animals or when plants and animals die and decay. THE HABER PROCESS Nitrogen is the most common gas in the atmosphere. It can be used to make ammonia when it is combined with hydrogen gas. This is a REVERSIBLE reaction – we looked at reversible reactions in the ‘chemical reactions’ booklet. Remember the blue bottle experiment? Reversible reactions go backwards and forwards. HISTORY The HABER PROCESS is a method of producing ammonia developed in WWI. The Germans needed nitrogen for making their explosives. When the Allies blocked off all trade routes going to and fron Germany, they lost all source of sodium nitrate and potassium nitrate, their source of nitrogen. 4 The Germans found their source of nitrogen from the air, which is 80% nitrogen. The Chemist FRITZ HABER developed the Haber Process. The Haber Process takes nitrogen from the air and combines it with hydrogen to form ammonia NH3 during a reversible reaction. Increasing the yield of ammonia in the Haber Process The ammonia produced in the Haber Process breaks down to from nitrogen and hydrogen which then recombine to form ammonia. This is because the Haber Process is a reversible reaction. For the manufacturer it is important to try to get the reaction to go forwards more than backwards. The more the reaction moves forwards the higher the yield of ammonia. It has been found that the reaction is more likely to move forwards under the following conditions: A high pressure A low temperature 5 Too high a pressure however would make the reaction vessel expensive to build and the process more dangerous. A compromise pressure of 200 atmospheres is therefore used. Too low a temperature would cause the reaction to become too slow. A compromise temperature of 450˚C is therefore used. Using Ammonia to make Fertilisers. Once ammonia has been produced it can be made into fertilisers to provide plants with nitrogen for growth. Firstly the ammonia is added to water to produce the alkali ammonium hydroxide. NH3(g) + H2O(l) NH4OH(aq) (ammonium hydroxide alkali) Secondly the ammonium hydroxide is added to an acid where it is then neutralised and an ammonium salt plus water is produced. The ammonium salt is the fertiliser. Example 1 - where ammonium hydroxide is neutralised with nitric acid to make the fertiliser ammonium nitrate. NH4OH(aq) + Ammonium hydroxide HNO3 NH4 NO3 nitric acid + H2O ammonium nitrate fertiliser Example 2 - where ammonium hydroxide is neutralised with sulphuric acid to make the fertiliser ammonium sulphate. 2NH4OH(aq) + Ammonium hydroxide H2SO4 (NH4)2 SO4 sulphuric acid ammonium sulphate fertiliser 6 + H2O Advantages of Fertilisers 1. Because they provide essential nutrients the same crops can be grown in the same soil year after year. 2. The Farmer can choose the fertiliser to fit the crop. For example, if the plant needs lots of potassium a Farmer could pick a fertiliser high in potassium. 3. Fertilisers improve the overall health of plants and generally make them less susceptible to disease. 4. Fertilisers produce larger crops so that less land is required to grow them. 5. More food can be grown in densely populated areas Disadvantages of fertilisers 1. Artificial fertilisers are very soluble and end up in our water supplies. Nitrates in the water supplies can cause nitrogen diseases in infants such as Blue Baby Syndrome. 2. High nitrate levels in water supplies have been linked to cancer. 3. Nitrate salts in ponds and lakes cause eutrophication (this is where algae grow on the surface and therefore starve the wildlife below of oxygen) 7 Some more tests! Testing for ammonium ions: All the positively charged ions we have looked at so far have been metal ions. Ammonium ions are also positive ions (NH4+). To test for ammonium ions such as those in our fertiliser ammonium sulphate, the solution being tested is heated with sodium hydroxide solution. If ammonium ions are present, ammonia gas is given off. For example: NH4Cl(aq) + NaOH(aq) NaCl(aq) + H2O(l) + NH3(g) The result of this test is that a potent smell of ammonia is given off Testing for ammonia gas You test the ammonia with damp red litmus paper, which turns blue in the gas. 8 END OF SUMMARY SHEETS Nitrogen Questions 1. Who discovered Nitrogen? _________________________________________ 2. Where can nitrogen compounds be found? _________________________________________ _________________________________________ 3. Describe Nitrogen gas _________________________________________ _________________________________________ 4. Describe what happens to a banana when it is dipped into liquid nitrogen and further hit with a hammer. _________________________________________ _________________________________________ 5. Where does nitrogen come from? ______________ 6. Why do plants need nitrogen? _________________________________________ _________________________________________ 7. Why can’t plants get nitrogen directly from the air? _________________________________________ _________________________________________ 9 8. Give three ways in which nitrogen can be converted into a useable form by plants (nitrogen fixation): a.________________________________________ _________________________________________ b.________________________________________ _________________________________________ c.________________________________________ _________________________________________ 9. Give a definition of nitrogen fixation? _________________________________________ _________________________________________ 10. Write a sentence about each of the following (use the summary sheets to help you):Fertiliser _______________________________________ _______________________________________ The Haber Process _______________________________________ _______________________________________ 10 Ammonia _______________________________________ _______________________________________ Ammonium hydroxide _______________________________________ _______________________________________ Sulphuric/Nitric acid _______________________________________ _______________________________________ Ammonium sulphate/nitrate _______________________________________ _______________________________________ 11. Fill in the gaps; The Haber Process - The Haber Process produces ________________ from ___________ and ______________. This is a _____________ reaction carried out at a temperature of __________ and under _____ atmospheres of pressure. REACTION CONDITIONS 11 12. From the graph below you will see that the reaction conditions actually used in the production of ammonia do not give the greatest yield of ammonia. a. Looking at the graph what temperature and pressure would give the best % (yield) of ammonia? Give units. Temp = _________ pressure ___________ Yield of ammonia under these conditions __________ b. Using multimedia science school, look at the reaction vessel containing nitrogen, hydrogen and ammonia. Increase both the temperature and pressure and complete the following: i. Increasing the pressure of gases in the Haber Process (increases/decreases) ______________ the yield of ammonia produced. Yield is the amount of nitrogen and hydrogen converted to ammonia. 12 ii. Increasing the temperature of gases in the Haber Process (increases/decreases) ______________ the yield of ammonia produced. iii. Which of the following combinations would result in the highest yield of ammonia? Circle the correct answer. Low temp, low pressure Low temp, high pressure High temp, high pressure iv. Is this combination used in the actual Haber Process? _____ v. What is the actual temperature used? ________ vi. What is the actual pressure used? ________ vii. What catalyst is used? ________ viii. Using the above graph or multimedia science school what is the actual yield of ammonia achieved by using these reaction conditions? ___________ Results obtained from the graph and multimedia science school may be different. This is because the graph in not particularly accurate. This exercise is simply to check that you can read a graph. Why why why? 13 13. So if the reaction conditions used do not give the greatest yield of ammonia why don’t they use a higher pressure and lower temperature in the Haber process?! Write your answers below. a. Why is a pressure of 200 atmospheres used in the Haber process when a higher pressure would yield more ammonia? _______________________________________________ _______________________________________________ b. Why is a temperature of 450˚C used when a lower temperature would produce a higher yield of ammonia? _______________________________________________ _______________________________________________ 14. Use the rest of this page to summarise the HABER PROCESS. Include the fact that it’s a reversible reaction. Ensure that you know the conditions – 400-500 C, 200-300 atmospheres, iron catalyst. 14 Using ammonia produced in the HABER PROCESS to make FERTILISERS. Neutralisation - a reaction of an acid with a base forming a salt and water. The base acts to remove the hydrogen ions present in the acid thus removing its acidity. Fertilisers are the salts produced when ammonia solution (NH4OH) acts as a base to neutralise acids such as sulphuric acid (hydrogen sulphate). Complete the following equation: ( swap partners to make the fertiliser AMMONIUM SULPHATE), Ammonium + hydrogen __________ + __________ Hydroxide sulphate __________ 15 __________ Making ammonium sulphate fertiliser from ammonia solution and sulphuric acid Ammonium sulphate (NH4)2SO4 is manufactured by neutralising sulphuric acid H2SO4 with ammonia (NH3) solution (NH4OH). Put the following sentences into the correct order by rewriting them into the table below and draw the apparatus required to carry out each step. Add ammonium hydroxide 5 cm3 at a time until the indicator turns green. This shows that the acid has been _______________- in the table draw a diagram of a conical flask containing 25cm3 sulphuric acid + U.I. with ammonium hydroxide being added using a measuring cylinder. Measure out 25cm3 sulphuric acid. Pour into a conical flask – in the table draw a diagram of a conical flask containing 25cm sulphuric acid. 3 Add 2-3 drops universal indicator to the sulphuric acid. The colour should become ___________________ - – in the table draw a diagram of a conical flask containing 25cm3 sulphuric acid with universal indicator being added from a pipette. Now pour the salt solution into an evaporating basin. Leave to crystallise. You should now have a sample of ammonium sulphate fertiliser – in the table draw an evaporating containing ammonium sulphate solution. Repeat the whole process with the now known volume of ammonium hydroxide (we don’t want indicator contaminating our final salt sample) - in the table draw a diagram of a conical flask containing 25cm3 sulphuric acid without U.I. with ammonium hydroxide being added using a measuring cylinder. 16 Plan – draw relevant equipment with a pencil and a ruler next to each step in the correct order. Steps for obtaining the fertiliser Equipment required. ammonium sulphate by neutralising sulphuric acid with ammonium hydroxide solution. 1. 2. 3. 4. 5. 17 Use page 6 to write a balanced chemical equation for the reaction of sulphuric acid with ammonia solution to produce ammonium sulphate and water. ____________ + ______________ ___________ + ________ Now carry out an experiment to isolate the fertiliser (salt) ammonium sulphate using ammonia solution (ammonium hydroxide) and sulphuric acid using the above plan. Results – fill in the text box below. Description of ammonium sulphate salt - You have just made ammonium sulphate fertiliser. Using page 6 of the summary sheets, write down a word and chemical equation to explain how you can make ammonium nitrate fertiliser. WORD EQUATION CHEMICAL EQUATION 18 The advantages and disadvantages of fertilisers. Use the resource sheet below and page 6 of the summary sheets to evaluate the advantages and disadvantages of fertiliser. Your teacher will advise you on how to approach this. 19 Fertilisers Fertilisers can be natural, such as manure and sewage sludge, or artificial, such as ammonium nitrate. Nutrients from fertilisers can get washed into rivers and leach into underground water sources. Eutrophication is the main environmental hazard associated with fertilisers. RESOURCE SHEET Why do we use fertilisers? Farmers use fertilisers to give the crops they grow extra nutrients than they would normally get just from the soil. This can help farmers to increase their crop yields. What is Eutrophication? Eutrophication is a condition in an aquatic ecosystem where high nutrient concentrations stimulate blooms of algae (e.g., phytoplankton). High nitrate levels in drinking waters are considered to be a hazard to both human and animal health. They are associated with some forms of cancers, such as those of the stomach and intestines. They may also cause "blue baby" syndrome in babies and young infants due to interference with the infants’ ability to carry oxygen in the blood Algae remove oxygen from the water, which makes it difficult for other plants and animals to get enough oxygen to survive. Blue baby syndrome is a rare but sometimes fatal disease that occurs primarily during the first four months of life. Symptoms include a blue discoloration of the lips, nose, and ears. Other symptoms include crying, vomiting and diarrhoea. It can be caused by a chemical called nitrate sometimes found at unsafe levels in tap water that is used to mix powdered formula. Extract from a Broadcast by Channel 4 in the UK, 1997 – ‘The tyranny of environmentalists’ Reaping the rewards of technology The densely populated First World is growing more trees because of modern high-yield farming techniques. 'In the United States, 'we use less land to produce more food than we used 50 years ago. We're able to use less land precisely because of chemical fertilisers and some of the very sophisticated techniques that we have. That allows you to preserve more land for wildlife habitat, for open space, for forests and other purposes. 'If you look at Africa, where they use very primitive agricultural techniques, which means they have to use very large amounts of land - that reduces the amount of land for endangered species like elephants and lions and tigers. It's also usually very bad agriculture - there's more soil erosion. So the environmental benefits of chemical fertilisers are really quite high.' 'It flies in the face of green theology,' adds Dennis Avery, Director of the Centre for Global Food Issues, 'but man-made chemicals today are helping to give us the most productive, most sustainable farming in the history of the planet. The best yields, the best soils, the more earthworms, the most soil bacteria, the most food for people, the most land left for wildlife all of it being achieved because of chemical fertilisers, pesticides, weedkillers.' Of course the climate in Africa is not as friendly to agriculture as it is in the Western world. However, scientists argue that with high-yield farming and irrigation Africa could feed itself many times over. The problem is not overpopulation, they 20 say, it is backward farming techniques. Teacher Demo Describe the test and the result of the test to identify the presence of an ammonium salt? ______________________________________________ ______________________________________________ ______________________________________________ Describe the test and the result of the test to identify the alkaline gas ammonia? ______________________________________________ ______________________________________________ ______________________________________________ 21