Chemistry_Grade_10-12 (1).pdf

2 industrial nitrogen fixation 370 chapter 19 global

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2. Industrial nitrogen fixation 370
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CHAPTER 19. GLOBAL CYCLES: THE NITROGEN CYCLE - GRADE 10 19.3 In the Haber-Bosch process, nitrogen (N 2 ) is converted together with hydrogen gas (H 2 ) into ammonia (NH 3 ) fertiliser. This is an artificial process. 3. Lightning In the atmosphere, lightning and photons are important in the reaction between nitrogen (N 2 ) and oxygen (O 2 ) to form nitric oxide (NO) and then nitrates. Interesting Fact erest Fact It is interesting to note that by cultivating legumes, using the Haber-Bosch process to manufacture chemical fertilisers and increasing pollution from vehicles and industry, humans have more than doubled the amount of nitrogen that would normally be changed from nitrogen gas into a biologically useful form. This has serious environmental consequences. 19.3 Nitrification Nitrification involves two biological oxidation reactions: firstly, the oxidation of ammonia with oxygen to form nitrite (NO 2 ) and secondly the oxidation of these nitrites into nitrates. 1. NH 3 + O 2 NO 2 + 3 H + + 2 e (production of nitrites ) 2. NO 2 + H 2 O NO 3 + 2 H + + 2 e (production of nitrates ) Nitrification is an important step in the nitrogen cycle in soil because it converts the ammonia (from the nitrogen fixing part of the cycle) into nitrates, which are easily absorbed by the roots of plants. This absorption of nitrates by plants is called assimilation . Once the nitrates have been assimilated by the plants, they become part of the plants’ proteins. These plant proteins are then available to be eaten by animals. In other words, animals (including humans) obtain their own nitrogen by feeding on plants. Nitrification is performed by bacteria in the soil, called nitrifying bacteria . Activity :: Case Study : Nitrates in drinking water Read the information below and then carry out your own research to help you answer the questions that follow. The negatively charged nitrate ion is not held onto soil particles and so can be easily washed out of the soil. This is called leaching . In this way, valuable nitrogen can be lost from the soil, reducing the soil’s fertility. The nitrates can then accumulate in groundwater, and eventually in drinking water. There are strict regulations that control how much nitrate can be present in drinking water, because nitrates can be reduced to highly reactive nitrites by microorganisms in the gut. Nitrites are absorbed from the gut and bind to haemoglobin (the pigment in blood that helps to transport oxygen around the body). This reduces the ability of the haemoglobin to carry oxygen. In young babies this can lead to respiratory distress, a condition known as ”blue baby syndrome”. 1. How is nitrate concentration in water measured? 2. What concentration of nitrates in drinking water is considered acceptable? You can use drinking water standards for any part of the world, if you can’t find any for South Africa.
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