NCERT Exemplar Class 11 Chemistry<\/a>. Here we have given NCERT Exemplar Class 11 Chemistry Chapter 14 Environmental Chemistry.<\/p>\nNCERT Exemplar Class 11 Chemistry Chapter \u00a014 Environmental Chemistry<\/h2>\n
Multiple Choice Questions<\/strong>
\nSingle Correct Answer Type
\n<\/strong>
\nQ1. Which of the following gases is not a greenhouse gas?<\/strong>
\n(a) CO <\/strong>
\n(b) 03<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong>
\n(c) CH4<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong>
\n(d) H2<\/sub>0 vapour
\nSol:<\/strong>(a) The gases which absorb solar energy near the earth\u2019s surface and then radiate it back to the earth are called greenhouse gases.
\n<\/strong><\/p>\nQ2. Photochemical smog occurs in warm, dry and sunny climate. One of the following is not amongst the components of photochemical smog, identify it.
\n<\/strong>(a) N02<\/sub> <\/strong>
\n(b) 03
\n<\/sub>(c) S02<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong>
\n(d) Unsaturated hydrocarbon<\/strong><\/p>\nSol:<\/strong> (c) The smog which is formed in the presence of sunlight is called photochemical smog. This occurs in the months of summer when N0<\/span><\/span>2<\/span><\/sub><\/span> and hydrocarbons are present in large amounts in the atmosphere. Concentration of 03<\/sub>, PAN, aldehydes and ketones increases up in the atmosphere. S0<\/span><\/span>2<\/span><\/sub><\/span> is not responsible for photochemical smog.<\/span><\/span><\/p>\nQ3. Which of the following statements is not true about classical smog?<\/strong>
\n(a) Its main components are produced by the action of sunlight on emissions <\/strong>of automobiles and factories.<\/strong>
\n(b) Produced in cold and humid climate.<\/strong>
\n(c) It contains compounds of reducing nature.<\/strong>
\n(d) It contains smoke, fog and sulphur dioxide.<\/strong>
\nSol:<\/strong> (a) Classical smog is initiated by a mixture of S02<\/sub>, particulates and high humidity in the atmosphere in cold conditions. A fog of H2<\/sub>S04<\/sub> droplets formed condenses on the particulates to form the smog. It is of reducing nature. The gases released by automobiles and factories are not responsible for classical smog.<\/p>\nQ4. Biochemical Oxygen Demand, \/BOD) is a measure of organic material present in water. BOD value less than 5 ppm indicates a water sample to be<\/strong>
\nSol:<\/strong> (a) The total amount of oxygen consumed by micro-organisms (bacteria) in decomposing organic matter present in certain volume of a sample of water is called Biochemical Oxygen Demand (BOD) of the water.
\nWater is considered to be pure if it has BOD less than 5 ppm, whereas highly polluted water has BOD more than 17 ppm. Thus, the water having BOD less than 5 ppm is rich in dissolved oxygen.<\/p>\nQ5. Which .of the following statements is wrong?
\n(a) Ozone is not responsible for greenhouse effect.
\n(b) Ozone can oxidize sulphur dioxide present in the atmosphere to sulphur trioxide.
\n(c) Ozone hole is thinning of ozone layer present in stratosphere.
\n(d) Ozone is produced in upper stratosphere by the action of UV rays on oxygen.<\/strong>
\nSol:<\/strong> (a) Ozone is also one of the greenhouse gases.<\/p>\nQ6. Sewage containing organic waste should not be disposed in water bodies because it causes major water pollution. Fishes in such a polluted water die because of<\/strong>
\n(a) large number of mosquitoes.<\/strong>
\n(b) increase in the amount of dissolved oxygen.\u00a0<\/strong>
\n(c) decrease in the amount of dissolved oxygen in water.<\/strong>
\n(d) clogging of gills by mud.<\/strong>
\nSol:<\/strong> (c) Organic waste consumes oxygen and therefore, dissolved oxygen in water decreases and fish in such polluted water die.<\/p>\nQ7. Which of the following statements about photochemical smog is wrong?<\/strong>
\n(a) It has high concentration of oxidizing agents.<\/strong>
\n(b) It has low concentration of <\/strong>oxidizing agent.<\/strong>
\n(c) It can be controlled by controlling the release of N02<\/sub>, hydrocarbons, ozone etc.<\/strong>
\n(d) Plantation of some plants like <\/strong>pinus helps in controlling photochemical<\/strong>
\nSol:<\/strong> (b) Photochemical smog is oxidizing in nature because it contains large concentration of oxidizing agents N02<\/sub> and 03<\/sub>.<\/p>\nQ8. The gaseous envelope around the earth is known as atmosphere. The lowest layer of this is extended up to 10 km from sea level. This layer is .<\/strong>
\n(a) Stratosphere <\/strong>
\n(b) Troposphere <\/strong>
\n(c) Mesosphere <\/strong>
\n(d) Hydrosphere <\/strong>
\nSol:<\/strong> (b) The atmosphere is divided into four major regions:
\n(i) Troposphere (ii) Stratosphere . (iii) Mesosphere and (iv) Thermosphere Troposphere is the lowest region of the atmosphere.<\/p>\nQ9. Dinitrogen and dioxygen are main constituents of air but these do not react with each other to form oxides of nitrogen because____________ .<\/strong>
\n(a) the reaction is endothermic and requires very high temperature.<\/strong>
\n(b) the reaction can be initiated only in presence of a catalyst.<\/strong>
\n(c) oxides of nitrogen are unstable.<\/strong>
\n(d) N2<\/sub> and 02<\/sub> are unreactive,<\/strong>
\nSol:<\/strong> (a) Major compounds of atmosphere are dinitrogen, dioxygen and water vapour.
\nN2<\/sub> = 78.08%, 02<\/sub> = 20.95%
\nBoth dinitrogen and dioxygen do not react with each other as nitrogen is an inactive gas. The triple bond in N2<\/sub> is very stable and its dissociation energy is very high. Both react with each other at very high temperature.<\/p>\n<\/p>\n
Q10. The pollutants which come directly in the air from <\/strong>source are called primary pollutants. Primary’pollutants are sometimes converted into secondary pollutants. Which of the following belongs to secondary air pollutants?<\/strong>
\n(a) CO <\/strong>
\n(b) Hydrocarbon<\/strong>
\n(c) Peroxyacetyl nitrate\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong>
\n(d) NO<\/strong>
\nSol:<\/strong> (c) Hydrocarbons present in atmosphere combine with oxygen atom produced by the photolysis of N02<\/sub> to form highly reactive intermediate called free \u00a0radical. Free radical initiates a series of reactions.Peroxyacetyl nitrate is formed, which Gan be said as secondary pollutant.
\n<\/p>\nQ11. Which of the following statements is correct?<\/strong>
\n(a) Ozone hole is a hole formed in stratosphere from which ozone oozes out.<\/strong>
\n(b) Ozone hole is a hole formed in the troposphere from which ozone oozes out.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 .<\/strong>
\n(c) Ozone hole is thinning of ozone layer of stratosphere at some places.<\/strong>
\n(d) Ozone hole means vanishing of ozone layer around the earth completely. <\/strong>
\nSol:<\/strong> (c) Two types of compounds have been found to be the most responsible for depleting the ozone layer. These are:
\n(i) NO and (ii) Chlorofluorocarbons.<\/p>\n<\/p>\n
Q12. Which of the following practices will not come under green chemistry?<\/strong>
\n(a) If possible, making use of soap made of vegetable oils instead of using synthetic detergents.<\/strong>
\n(b) Using H2<\/sub>02<\/sub> for bleaching purpose instead of using chlorine based bleaching agents.<\/strong>
\n(c) Using bicycle for traveling small distances instead of using petrol\/diesel based vehicles.<\/strong>
\n(d) Using plastic cans for neatly storing substances.<\/strong>
\nSol:<\/strong> (d) Plastic is non-biodegradable polymer. Hence, it does not come under green chemistry. Green chemistry includes processes which lead to minimum pollution and less harm to the environment.<\/p>\nMore than One Correct Answer Type<\/strong><\/p>\nQ13. Which of the following conditions shows the polluted environment?<\/strong>
\n(a) pH of rain water is 5.6.<\/strong>
\n(b) Amount of carbon dioxide in the atmosphere is 0.03%.<\/strong>
\n(c) Biochemical oxygen demand is 10 ppm.<\/strong>
\n(d) Eutrophication
\n<\/strong>Sol: (c, d) Polluted water may contain nutrients for the growth of algae, which covers the water surface and reduces the oxygen concentration in water. This leads to anaerobic condition, accumulation of obnoxious decay and animal death. This is process of eutrophication.<\/p>\nThe amount of oxygen required by bacteria to break down the organic matter present in a certain volume of sample of water is called Biochemical Oxygen Demand. Clean water would have BOD value of 5 ppm whereas highly polluted could have BOD value of 17 ppm or more.<\/p>\n
Normally rain water has pH of 6 due to H+<\/sup> ion formed by reaction of rain water with carbon dioxide in the atmosphere. When the pH of the rain water drops below 5.6, it is called acid rain.<\/p>\nQ14. Phosphate containing fertilizers cause water pollution. Addition of such compounds in water bodies causes <\/strong>
\n(a) enhanced growth of algae<\/strong>
\n(b) decrease in amount of dissolved oxygen in water<\/strong>
\n(c) deposition of calcium phosphate <\/strong>
\n(d) increase in fish population
\nSol:<\/strong> (a, b) Fertilizers containing phosphate present in water help in the excessive growth of aquatic plants and algae. Micro-organisms which decompose these plants consume oxygen. As a result, the amount of dissolved oxygen in the water decreases.<\/p>\nQ15. The acids present in acid rain are________ .<\/strong>
\n(a) Peroxyacetylnitrate\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/strong>
\n (b) H2<\/sub>C03
\n<\/sub>(c) HN03<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/strong>
\n (d) H2<\/sub>S04
\n<\/sub><\/strong><\/p>\nSol:<\/strong> (b, c, d) C02<\/sub> is slightly soluble in water forming carbonic acid.
\n\u00a0<\/sub><\/strong>Co2<\/sub> + H2<\/sub>O \u2192 H2<\/sub>Co3
\n<\/sub>The oxides of nitrogen undergo oxidation reaction followed by reaction with water vapours to form nitric acid.<\/span><\/span><\/p>\n2NO + 02<\/sub>\u2192 2N02
\n<\/sub>2N02<\/sub> + H2<\/sub>0 \u2192 HN03<\/sub> + HNO2
\n<\/sub>
\nThe oxidation of S02<\/sub> into S03<\/sub> occurs in the presence of dust particles or metal ions. The S03<\/sub> then reacts with water vapours to form H2<\/sub>S04<\/sub>.<\/p>\n <\/sub><\/strong><\/p>\nQ16. The consequences of global warming may be .<\/strong>
\n(a) increase in average temperature of the earth<\/strong>
\n(b) melting of Himalayan Glaciers –<\/strong>
\n(c) increased biochemical oxygen demand<\/strong>
\n(d) eutrophication<\/strong>
\nSol:<\/strong> (a, b) The rate at which solar radiation is reaching the earth is constant but the amount of C02<\/sub> in the air is increasing. Consequently, the heat radiated back to the earth will increase and the temperature of the earth surface will also increase.
\nThis increase in temperature will disturb the thermal balance on the earth and could cause glacier \u00a0and ice caps to melt.<\/p>\nShort Answer Type Questions<\/strong>
\nQ17. Greenhouse effect leads to global warming. Which substances are responsible for greenhouse effect?<\/strong>
\nSol:<\/strong> The heating of earth due to trapping of radiation is called greenhouse effect. The gases such as C02<\/sub>, CH4<\/sub>, N2<\/sub>0, CFC13<\/sub>, CF2<\/sub>C12<\/sub>,03<\/sub> etc. trap these radiations and are called greenhouse gases.<\/p>\nQ18. Acid rain is known to contain some acids. Name these acids. From where do they come in rain?<\/strong>
\nSol:<\/strong>\u00a0Acid rain contains acids such as HN03<\/sub>, H2<\/sub>S04<\/sub> and H2<\/sub>C03<\/sub> (along with small amount of HC1).
\nHN03<\/sub> is formed by the oxidation of NO present in air to N02<\/sub> and N03<\/sub> and subsequent dissolution in water. H2<\/sub>S04<\/sub> is formed by the oxidation of S02 <\/sub>present in air to S03<\/sub> and subsequent dissolution in water.
\nH2<\/sub>C03<\/sub> is formed by the dissolution of C02<\/sub> of the air in water.<\/p>\nQ19. Ozone is a toxic gas and is a strong oxidizing agent, even then its presence in the stratosphere is very important. Explain what would happen if ozone from this region is completely removed.<\/strong>
\nSol:<\/strong> Ozone layer acts as a protective umbrella and does not allow the harmful UV radiations to reach the earth\u2019s surface. If ozone is completely removed from the stratosphere, the UV radiations will fall directly on the humans causing skin cancer and on the plants affecting plant proteins.
\nQ20. Dissolved oxygen in water is v\u00a3ry important for aquatic life. What processes are responsible for the reduction of dissolved oxygen in water?<\/strong>
\nSol:<\/strong>\u00a0The discharge of human sewage and organic waste from pulp and paper
\nindustry and presence of leaves, grass, trash etc. in water due to run off result ‘ in phytoplankton growth. The microorganisms which decompose this organic matter need oxygen. Hence, the amount of oxygen in water of lakes etc. decreases.<\/p>\nQ21. On the basis of chemical reactions involved, explain how do chlorofluoro- carbons cause thinning of ozone layer in stratosphere.<\/strong>
\nSol:<\/strong> Chlorofluorocarbons are stable compounds. They move to stratosphere by random diffusion. These undergo decomposition in the presence of sunlight to release Cl atoms. These Cl atoms cause catalytic chemical reactions and cause significant depletion of ozone layer as shown below:<\/p>\n
\nSince the free radicals use ozone and convert it to oxygen, they cause thinning of ozone layer in stratosphere.<\/span><\/span><\/p>\nQ22. What could be the harmful effects of improper management of industrial and domestic solid waste in a city?<\/strong>
\nSol:<\/strong> If domestic waste in a city is not properly managed, it may find its way into . sewers or may be eaten up by the cattle. The non-biodegradable waste like polythene bags, metal scrap etc. choke the sewers. The polythene bags, if swallowed by the cattle, can result into their death. Similarly, if industrial waste is not properly managed, it will cause pollution of the air, soil and water.<\/p>\nQ23.During an educational trip, a student of Botany saw a beautiful lake in <\/strong>a , village. She collected many plants from that area. She noticed that villagers were washing clothes around the lake and at some places, waste material from houses was destroying its beauty. After few years, she visited the same r lake again. She was surprised to find that the lake was covered with algae, stinking smell was coming out and its water had become unusable. Can you explain the reason for this condition of the lake?<\/strong>
\nSol:<\/strong> Disposing of waste material and washing clothes in lake water makes the water rich in nutrients like phosphate. It enhances algae growth. Such profuse ‘ algal growth covers the water surface which reduces oxygen concentration in water. This leads to anaerobic conditions with accumulation of dead and decaying water animals, thus, leaving the water with stinking smell and making it unusable.<\/p>\nQ24. What are biodegradable and non-biodegradable pollutants?\u00a0<\/strong>
\nSol:<\/strong> Biodegradable pollutants are those which can be decomposed by bacteria. For example, dust particles, sewage, cow dung etc.\u00a0Non-biodegradable pollutants are those which cannot be decomposed by bacteria. For example, plastic materials, mercury, aluminium, DDT, etc.<\/p>\nQ25. What are the sources of dissolved oxygen in water?<\/strong>
\nSol:<\/strong> Sources of dissolved oxygen in water are (i) Photosynthesis (ii) Natural aeration (iii) Mechanical aeration.<\/p>\nQ26. What is the importance of measuring BOD of a water body?<\/strong>
\nSol:<\/strong> BOD is the measure of level of pollution caused by organic biodegradable material in terms of how much oxygen will be required to break down the organic material biologically. Clean water would have BOD values less than 5 ppm while highly polluted water could have a BOD value of 17 ppm or more.<\/p>\nQ27. Why does water covered with excessive algal growth become polluted?<\/strong>
\nSol:<\/strong> Presence of excessive algal growth shows that water contains a lot of
\nphosphate due to inflow of fertilizers, etc from the surroundings. Hence, such a sample of water is polluted.<\/p>\nQ28. A factory was started near a village. Suddenly villagers started feeling the presence of irritating vapours in the village and cases of headache, chest pain, cough, dryness of throat and breathing problems increased. Villagers blamed the emissions from the chimney of the factory for such problems. Explain what could have happened. Give chemical reactions for the support of your explanation.
\nSol:<\/strong>The symptoms observed in the villagers show that oxides of nitrogen and sulphur must be coming out of the chimney. This is due to combustion of fossil fuels like coal, oil, natural gas, gasoline, etc. to produce high temperatures at which oxidation of atmospheric nitrogen takes place forming NO and N02<\/sub>:
\n
\nS02<\/sub> is produced due to combustion of sulphur containing coal and fuel oil or roasting of sulphide ores like iron pyrites (FeS2<\/sub>), copper pyrites (CuFeS2<\/sub>), etc.<\/p>\nCu2<\/sub>S + 02<\/sub>\u21922Cu + S02<\/sub><\/p>\nQ29. Oxidation of sulphur trioxide in the absence of a catalyst is a slow process but this oxidation occurs easily in the atmosphere. Explain how does this happen. Give chemical reactions for the conversion of S02<\/sub> into S03<\/sub>.<\/strong>
\nSol:<\/strong> The presence of particulate matter in polluted air catalyses the oxidation of S02<\/sub> to S03<\/sub>. The reaction is also promoted by ozone and hydrogen peroxide.<\/p>\n
\nQ30. From where does ozone come in the photochemical smog?<\/strong>