NotesDownload Atmosphere & Water NotesComposition of air
Fractional distillation to separate components of air
Percentage Composition of Oxygen in Air
OxygenA. RespirationOxygen is essential for all plant and animal life on earth. The process by which living organisms produce energy from their food is called respiration. Oxygen is essential for this process: sugar + oxygen ---> carbon dioxide + water + energy
3 things are required for combustion
Uses of Oxugen
Oxides: oxygen combined with elementsOxygen is a reactive gas and will combine directly with most metals and non-metals to form oxidesReaction with metals
Many elements burn in oxygen with colored flames to produce the corresponding oxide. Across the periodic table, the properties of the oxides of these elements change from basic to acidic in nature (metals to non-metals) Basic oxides are formed by metals in Groups I, II, and III. They are generally ionic oxides and are white solids. Metal oxides
Non-metal oxides
The non-metals in Groups IV, V, VI and VII form covalent oxides. Such oxides are mainly gases or liquids but giant covalent oxides like silicon dioxide are solids Aluminium oxide is both basic and covalent and is therefore an amphoteric oxide. Air Pollution: Harmful substances in the airMain Pollutant gases:1) carbon monoxide, COComes from: - When fuels like petrol and diesel are burnt in an internal combustion engine, the amount of oxygen present is limited, so carbon monoxide gas is formed, instead of carbon dioxide gas. - Unburnt hydrocarbons - forest fires Hazards: - Combines with haemoglobin when inhaled, which produces carboxyhaemoglobin that reduces efficiency of haemoglobin to transport oxygen. - Cells then die. Prevention: - Install catalytic converters in cars - Reduce number of cars on road - Create efficient engines in cars to ensure complete hydrocarbon combustion 2) sulphur dioxide, SO2 Comes from: - Combustion of fossil fuels containing sulphur impurities - volcanic eruptions Hazards: - Lung irritant - eye irritant - acid rain Prevention: - Prevent using fuels containing sulphur impurities, e.g. coal - Reduce the sulphur impurities inside fossil fuels - Spray exhaust gases from factories with water/hydrated CaO/alkalis to absorb sulphur dioxide before it’s released into the atmosphere - Add CaO to soil and rivers to neutralize acid rain 3) oxides of nitrogen, NO Comes from: - Lightning activity - forest fires - internal combustion engines (as nitrogen oxides are formed by oxygen and nitrogen under high temperature) --> Poisonous oxides of nitrogen are also formed from the electrical spark which passes through the air/petrol mixture. - power stations Hazards: - Eutrophication - lung damage - acid rain Prevention: - Install catalytic converters in cars - Design car engines which run at lower temperatures Notes: Reactions of oxides of sulphur and nitrogen The oxides of sulphur and nitrogen are acidic gases and are water-soluble. They dissolve to form acid rain. The main source of these pollutant gases is from the burning of fuels, especially those in petrol and diesel engines. All oils and fuels contain sulphur, and when they are burnt, sulphur dioxide gas is formed. In power stations, large quantities of this gas are produced, which dissolve in water in the atmosphere to form sulphurous acid (sulphuric acid) SO2 (g) + H2O (l) --> H2SO3 (aq) 4) Methane Comes from: - Decomposition of vegetable matter - rice field - cattle ranching - natural gas - mines Hazards: - highly flammable - greenhouse gas Prevention: - Cattle and other ruminant animals should be given improved diet - Animal manure and rotting vegetation can be used as biomass fuel 5) Unburnt hydrocarbons Comes from: - Internal combustion engines - Because of the limited supply of air inside the engines some of it remains unburnt and escapes as gaseous hydrocarbons. Hazards: - Carcinogenic - forms photochemical smog - can act as greenhouse gases contributing to global warming. Prevention: - Install catalytic converters in cars - Reduce number of cars on road - Create efficient engines in cars to ensure complete hydrocarbon combustion 6) Ozone Comes from: - It is formed when an electrical spark passes through air. This is because it reacts with the UV radiation in sunlight to produce a 'photochemical smog'. - It is an allotrope (two/three different forms of a pure element) of oxygen having structural formula O3 having characteristic odour. - High up in the atmosphere ozone is beneficial as it helps to filter out high levels of UV radiation Hazards - It reacts with unburnt hydrocarbons to form photochemical smog that causes headache, eye, nose and throat irritation. - It corrodes and kills plants and trees Prevention - Don’t use CFCs/replace it with HCFCs which destroys faster. Notes: Catalytic converters - One way to reduce pollution from cars is to fit catalytic converters to our exhausts. - Inside the converter is a special metal-like platinum which acts as a catalyst. - It converts the poisonous exhaust gases of CO and oxides of nitrogen into harmless gases like carbon dioxide and nitrogen. - It does this by transferring oxygen atoms from the oxides of nitrogen to the CO. 2CO (g) + 2NO (g) --> 2CO2 (g) + N2 (g) 7) Dust and Smoke - The larger, heavier dust particles will settle quickly but the smaller particles may remain suspended in the air for a long time. Comes from: - building work - mining activities - forest fires - incomplete combustion of fuels. Hazards: - irritate lungs, causing bronchitis and other lung-related diseases. 8) Lead compounds Comes from: - Combustion of leaded petrol in car engines - lead compounds are added to petrol to make it heavier so that it does not ignite too soon. Hazards: - when breathed in can build up inside the body and are toxic and poisonous - Causes lead poisoning which leads to brain damage. Natural compounds of carbonCarbon Cycle- Carbon dioxide is produced mainly by respiration. Here, sugars such as glucose are converted into carbon dioxide and water, giving out energy (exothermic) Respiration of glucose equation: - Carbon dioxide is also produced by combustion of fuels, in factories, and in the home - The carbon dioxide is then absorbed by plants, by photosynthesis. Energy is absorbed (endothermic) from the sun, and used to build up simple sugars. Photosynthesis equation: - Animals eat plants, and in turn, they themselves get eaten by other animals. So the carbon originally in the atmosphere ends up in every living plant and animal. Upon death, the carbon is released by bacteries and fungi, to return to the atmosphere as carbon dioxide. The cycle is then repeated. MCQ Questions1. Which atmospheric pollutants, emitted by internal combustion engines, are reacted together to convert them to less harmful products?a. carbon monoxide and nitrogen dioxide b. carbon monoxide and unburned hydrocarbons c. nitrogen dioxide and sulfur dioxide sulfur dioxide and unburned hydrocarbons 2. The global atmospheric concentration of carbon dioxide has increased in the last 200 years. What could be causing this increase? 1. emissions from motor vehicles 2. photosynthesis 3. power stations using coal and oil a. 1 and 2 only b. 1 and 3 only c. 2 and 3 only d. 1, 2, and 3 3. Which statements about the pollutant carbon monoxide are correct? 1. it is a colourless, odourless gas 2. it is formed by incomplete combustion of natural gas 3. it reacts with haemoglobin in the blood a. 1 and 2 only b. 1 and 3 only c. 2 and 3 only d. 1, 2, and 3 4. Which gas is not produced when hydrocarbons are burnt in the internal combustion engine a. carbon dioxide b. carbon monoxide c. hydrogen d. nitrogen oxides 5. Photochemical smog is seen in many industralised cities. Which of the following is not responsible for its formation? a. nitrogen dioxide b. sulphur dioxide c. pentane d. ozone MCQ Answers1. a2. b 3. d 4. c 5. b Structured Question Worked Solutions1. The exhaust gases of a motor car contain several pollutants, among them carbon monoxide and oxides of nitrogen. The flowchart below shows the arrangement of a two-stage catalytic converter in a motor car engine and exhaust system.In the first converter, carbon monoxide reacts with oxygen. In the second converter, nitrogen oxides decompose into nitrogen and oxygen. ai. Explain how carbon monoxide is produced in a motor car engine. aii. Give the name of the gas that is produced in the first converter. Write an equation to show its production. aiii. Why is carbon monoxide a pollutant? b. Two oxides of nitrogen are nitrogen dioxide, NO2, and nitrogen monoxide, NO. i. Write an equation to show the decomposition of one of these oxides. ii. Why are oxides of nitrogen pollutants? ci. What is a catalyst? cii. Suggest why the catalysts in the first and second converters are different. Solution 1ai. As a result of incomplete combustion of petrol 1aii. carbon dioxide 2CO (g) + O2 (g) --> 2CO2 (g) 1aiii. Carbon monoxide, when breathed in, prevents blood from transporting oxygen. This is because CO can become strongly bonded to haemoglobin (present in red blood cells) and thus prevents the haemoglobin from transporting oxygen. The victim may die after some time due to lack of oxygen. 1bi. 2NO2 (g) --> N2 (g) + 2O2 (g) 1bii. They are acidic and cause acid rains, thereby corroding buildings and killing plants. 1ci. A catalyst is a substance that changes the rate of a reaction and itself remains chemically unchanged at the end of the reaction. 1cii. Because different catalysts catalyse different reactions. The catalyst that catalyses the production of CO2 from CO may not catalyse the decomposition of oxides of nitrogen and vice versa. 2a. Pure oxygen is obtained from air and is used as an aid to breathing in hospital oxygen masks. i. describe in outline how pure oxygen is obtained from air ii. give a commercial use for oxygen other than as an aid to breathing b. One problem with oxygen is that it is the essential element in causing corrosion of metals. One method of limiting corrosion is known as 'sacrificial protection'. Explain what is meant by sacrificial protection. Solution 2ai. By fractional distillation of liquid air. Fractional distillation is a method used to separate liquids based on the difference in their boiling points. 2aii. acetylene in welding 2b. A metal more reactive than the metal to be protected is connected to the metal to be protected. This more reactive metal corrodes in preference to the protected metal. This is called sacrificial protection. 3. Complete the following table about atmospheric pollutants.
Solution
4. Ozone occurs in the upper atmosphere. a. why is ozone in the upper atmosphere important? b. state one type of compound that is responsible for ozone depletion Solution 4a. The ozone layer acts as a barrier that absorbs harmful UV rays from the sun, preventing it from reaching earth. 4b. chlorofluorocarbons 5. Coal-burning power stations produce sulphur dioxide and oxides of nitrogen. These two gases cause acid rain. a. Nitric oxide, NO, is made in a power station when nitrogen and oxygen react together. Write the equation for this reaction. b. Many coal-burning power stations are now fitted with a flue gas desulphurisation plant which removes sulphur dioxide and nitrogen dioxide from the gaseous emissions. In a flue gas desulphurisation plant, powdered calcium carbonate reacts with sulphur dioxide as shown. SO2 (g) + CaCO3 (s) --> CaSO3 (s) + CO2 (g) i. suggest why the calcium carbonate is powdered ii. calculate the mass of calcium carbonate needed to react with 8000 kg of sulphur dioxide iii. nitrogen dioxide also reacts with calcium carbonate. suggest the name of the solid product of this reaction. c. In the air sulphur dioxide reacts with nitrogen dioxide forming sulphur trioxide. The reactions that take place are shown in the equation SO2 + NO2 --> SO3 + NO 2NO + O2 --> 2NO2 Suggest the role of nitrogen dioxide in these reactions. Explain your answer. d. Sulphur dioxide is used in the Contact Process to make sulphuric acid. Describe the conditions and name the catalyst in the Contact Process. Solution 5a. N2 + O2 --> 2NO 5bi. To increase the surface area in order to absorb more SO2 gas 5bii. Mr of SO2 = 64 no. of moles of SO2 = (8000 X 103) / 64 = 1.25 X 105 no. of moles of CaCO3 reacted = 1.25 x 105 mass of CaCO3 reacted = 1.25 x 105 x 100 = 1.25 x 107 = 12500 kg 5biii. calcium nitrate 5c. As an oxidising agent because it oxidises SO2 to SO3 in reaction 1 As a catalyst because NO2 is reformed at the end of reaction 2 and therefore, the original role of NO2 in reaction 1 has not been used up at the end of the reaction. 5d. 450oC, 2 atmospheric pressure catalyst: Vanadium(V) oxide |
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