1、Ch.31 p. 1Chapter 31 Nitrogenous Fertilizers31.1 Why need fertilizers?A. Plants as fundamental food sourceWe eat a variety of plants directly. These are mainly crops, including cereals (e.g. wheat, rice), vegetables and fruits. We also need livestock and poultry for their meat, milk and eggs. These
2、animals feed on grass or cereals. So in this way, we are eating plants indirectly.B. More food for ever-growing populationToday, there are over 6 billion people on the Earth. It has been estimated that about 10% of the world population are starving. The ever-growing population needs more and more fo
3、odC. What plants need from soilNutrient Importance to plant growth Effects of shortageNitrogen Essential for synthesis of proteins and chlorophyll Needed for strong, healthy stems and leaves Poor growth Small and yellow leavesPhosphorus Needed to produce a good root system Essential for formation of
4、 seeds Poor root development Plant grows slowly Small seeds Small fruitsPotassium Needed for the production of flowers and fruits. Increases plants resistance to deceases and poor weather Seldom flowering Small fruits Plant dies easily in poor conditionsD. Essential elements for plants1. Plants obta
5、in carbon from carbon dioxide in the atmosphere.2. Plants obtain hydrogen and oxygen from water.3. Nitrogen, phosphorus and potassium (NPK) are three major elements needed for plant growth. Absence of NPK would slow down growth or even cause death of plants.4. Plants take NPK from soil.5. Fertilizer
6、s are added to soil to replenish(補充) NPK for plant growth.Lightning causes nitrogen and oxygen in air to react to form nitrogen oxides. These eventually change to nitric acid and then nitrates in soil.Some bacteria can change nitrogen into nitrates. They usually live in root nodules in plants such a
7、s peas and beans.E. Summary1. Plants are fundamental food source for human beings. Fertilizers canincrease agricultural yield and improve quality of crops to meet the demand for the demand for the ever growing population.2. Fertilizers are added to soil to replace nitrogen, phosphorus and potassium
8、which have been removed when plants are grown and harvested.Study example 31.1 to know about the importance of nitrogen to plant growth on p. 232.Ch.31 p. 231.2 Types of fertilizersA. Fertilizers are added to soil to provide important nutrients needed for plant growth. They are usually inorganic sal
9、ts that contain one or more of nitrogen, phosphorus and potassium. Inorganic fertilizers are also called artificial fertilizers. They are extensively used nowadays. There are also organic fertilizers, which are less common today. These include manure, dried blood, bone meal and wood ash. B. Nitrogen
10、ous Fertilizers1. Nitrogen is essential in making amino acids and protein in plants.2. The atmosphere contains about 80% nitrogen gas (N2). Plants cannot use nitrogen in the atmosphere to make proteins.3. Plants can obtain nitrogen from(a) nitrates (NO3-) or nitric acid (HNO3) formed in lightning.(b
11、) symbiotic(共生) nitrogen fixing bacteria in legumes. (豆科植物)(c) dead plants and animals.(d) manure of animals(e) artificial fertilizers (nitrogenous or NPK)4. Common artificial nitrogenous fertilizers include (water soluble and has a quick effect)(a) ammonium sulphate, (NH4)2SO4(b) ammonium nitrate ,
12、 NH4NO3(c) ammonium dihydrogen phosphate, NH4H2PO4(d) diammonium hydrogen phosphate, (NH4)2HPO4(e) urea (尿素), (NH 2)2CO.5. Nitrogen content in nitrogenous fertilizers.% mass of nitrogen in a fertilizer= atomic mass of nitrogen X number of nitrogen atoms in formula of the fertilizer x 100%formula mas
13、s of the fertilizerStudy P. 234 example 31.2 and do Q 31.331.3 Making ammonium sulphateAmmonium sulphate is a nitrogenous fertiliser and it is also a salt. It can be prepared by the neutralization of aqueous ammonia and dilute suphuric acid.)(42)(42)(3(2aqaqaq SONHSONH The solution is then evaporate
14、d to dryness in order to get ammonium sulphate crystals.Expt 29.1Ch.31 p. 331.4 AmmoniaA. Haber processAmmonia is manufactured by the direct combination of nitrogen and hydrogen industrially. The method is known as the Haber process.In the Haber process, nitrogen and hydrogen combine under special c
15、onditions: N2(g) + 3H2(g) 2NH3(g) H = -92 kJ mol-1Conditions: 200 atmospheres, 500, finely divided iron.Example 31.3 p. 238B. Preparation of ammonia in the laboratoryAmmonium salt + alkali salt + ammonia + watere.g. (NH4)2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2NH3(g) + 2H2O(l)C. Physical properties1. Amm
16、onia is a colourless gas with a choking and pungent smell.2. It is less dense than air.3. It is very soluble in water.4. It turns red litmus paper blue. Therefore, It is an alkaline gas.5. It is toxic.Q 31.4 p. 239D. Uses of ammonia1. to make fertilizers.2. To manufacture nitric acid.3. As a degreas
17、ing agent, e.g. window cleaner.4. As a refrigerant in some industrial refrigerating plants.Ch.31 p. 431.5 Nitric AcidOstwald Process : Nitric acid is manufactured by the catalytic oxidation of ammonia 4NO(g) + 6H2O(l) PtcalystggONH)(2)(3542NO(g) + O2(g) 2NO2(g)4NO2(g) + O2(g) + 2 H2O(l) 4HNO3(aq)A.
18、Uses of nitric acid1. to make fertilizers such as ammonium nitrate.2. To manufacture explosives3. To make synthetic fibres such as nylon.4. Refining metals, etching metals and in photography.31.6 Sulphuric acidA. Manufacture of sulphuric acid by the Contact Process.1. Preparation and purification of
19、 sulphur dioxide.2. Catalytic oxidation of sulphur dioxide to sulphur trioxide.3. Conversion of sulphuric trioxide to sulphuric acid.(1) Preparation and purification of sulfur dioxidea. By burning sulphur in air S(s) + O2 (g) S O2 (g)b. By roasting sulfide ores in airIron pyrites 4FeS2(s) + 11O2(g)
20、2Fe2O3(s) + 8SO2(g)Zinc blende 2ZnS(s) + 3O2(g) 2ZnO(s) + 2SO2(g)(2) Catalytic oxidation of sulphur dioxide to sulphur trioxideSulphur dioxide and oxygen react according to the equation:2SO2(g) + O2(g) 2SO3(g) H = -196 kJ mol -1The sulphur dioxide and air mixture is passed along hot pipes containing
21、 vanadium(V) oxide (V2O5) catalyst at 450oC and 1 atm.Ch.31 p. 5(3) Conversion of sulphur trioxide to sulphuric acidThe hot sulphur trioxide thus formed is passed back to the heat exchanger to heat up the incoming gases (SO2 and air). It is then dissolved in concentrated sulphuric acid (98% H2SO4 by
22、 mass) in the absorption tower to form oleum (or fuming sulphuric acid).H2SO4(l) + SO3(g) H2S2O7(l)oleumSulphur trioxide is not dissolved directly in water to form sulphuric acid. (p. 243)B. Uses of sulphuric acida. Manufacture of fertilizers such as superphosphate and ammonium sulphate.b. Manufactu
23、re of additives (e.g. barium sulphate, calcium sulphate) in white paints.c. Manufacture of soapless detergentsd. Manufacture of synthetic fibres.e. To make lead acid cells.Q 31.6 p. 244C. Preparing and testing sulphur dioxide in watera. Preparation of sulfur dioxideBy burning sulphur in air S(s) + O
24、2 (g) S O2 (g)b. Properties of sulphur dioxide* A colourless gas with a characteristic choking smell of burning sulphur.* It is fairly poisonous. * It is denser than air. * It is very soluble in water.* It is an acidic gas which turns wet blue litmus paper red.* It is reducing agent. It can reduce f
25、rom orange Cr2O72-(aq)/H+(aq) to green (Cr3+(aq) ).Itself oxidize from SO2 (O.N. +IV) to SO42-(aq) (O.N. +VI)31.7 Setting up a chemical plant.A. Availability of resourcesa. closeness to source of raw materialsb. good water supplyc. cheap fuel supplyd. sufficient cheap land resourcese. good supply of labour.B. Demand and delivery of productsa. possible customers nearbyb. good transport.C. Objections from local people on air, water and noise pollution, fear of risk of explosion.Ch.31 p. 6Exercise M. C. 19-3234, 35, 36 , 39, 40, 41, 42, 44, 45, 47, 48, 50
