Chemistry_Grade_10-12 (1).pdf

However all these natural processes of maintaining

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However, all these natural processes of maintaining soil nutrients take a long time. As populations grow and the demand for food increases, there is more and more strain on the land to produce food. Often, cultivation practices don’t give the soil enough time to recover and to replace the nutrients that have been lost. Today, fertilisers play a very important role in restoring soil nutrients so that crop yields stay high. Some of these fertilisers are organic (e.g. compost, manure and fishmeal), which means that they started off as part of something living. Compost for example is often made up of things like vegetable peels and other organic remains that have been thrown away. Others are inorganic and can be made industrially. The advantage of these commercial fertilisers is that the nutrients are in a form that can be absorbed immediately by the plant. Definition: Fertiliser A fertiliser is a compound that is given to a plant to promote growth. Fertilisers usually provide the three major plant nutrients and most are applied via the soil so that the nutrients are absorbed by plants through their roots. When you buy fertilisers from the shop, you will see three numbers on the back of the packet e.g. 18-24-6. These numbers are called the NPK ratio , and they give the percentage of nitrogen, phosphorus and potassium in that fertiliser. Depending on the types of plants you are growing, and the way in which you would like them to grow, you may need to use a fertiliser with a slightly different ratio. If you want to encourage root growth in your plant for example, you might choose a fertiliser with a greater amount of phosphorus. Look at the table below, which gives an idea of the amounts of nitrogen, phosphorus and potassium there are in different types of fertilisers. Fertilisers also provide other nutrients such as calcium, sulfur and magnesium. Table 23.3: Common grades of some fertiliser materials Description Grade (NPK %) Ammonium nitrate 34-0-0 Urea 46-0-0 Bone Meal 4-21-1 Seaweed 1-1-5 Starter fertilisers 18-24-6 Equal NPK fertilisers 12-12-12 High N, low P and medium K fertilisers 25-5-15 23.4.3 The Industrial Production of Fertilisers The industrial production of fertilisers may involve several processes. 451
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23.4 CHAPTER 23. THE CHEMICAL INDUSTRY - GRADE 12 1. Nitrogen fertilisers Making nitrogen fertilisers involves producing ammonia , which is then reacted with oxy- gen to produce nitric acid . Nitric acid is used to acidify phosphate rock to produce nitrogen fertilisers. The flow diagram below illustrates the processes that are involved. Each of these steps will be examined in more detail. (a) HABER PROCESS The production of ammonia from nitrogen and hydrogen (b) OSTWALD PROCESS Production of nitric acid from ammonia and oxygen (c) NITROPHOSPHATE PROCESS Acidification of phosphate rock with nitric acid to produce phosphoric acid and calcium nitrate Figure 23.9: Flow diagram showing steps in the production of nitrogen fertilisers (a) The Haber Process
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