Important Questions for CBSE Class 11 Chemistry Chapter 14: Environmental Chemistry

Important Questions for CBSE Class 11 Chemistry Chapter 14: Environmental Chemistry includes the study of the origin, reactions, and effects of chemical species in the environment. It will help the studens in understanding various topics related to the environment like pollution, reasons for global warming, the greenhouse effect and acid rain. Identifying the reasons leading to these problems and suggesting appropriate strategies for controlling environmental pollution is explained in the chapter Environmental Chemistry.

Also Read: Effects of Climate Change

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Very Short Answer Questions [1 mark Question]

Ques: What should be the pH of drinking water?

Ans: The pH of clean drinking water must be between 6.5−8.5

Ques: Name two herbicides used to kill weeds.

Ans: Sodium chlorate (NaClO3) and Sodium arsenite (Na3AsO3)

Ques: Which zone is called the ozonosphere?

Ans: Stratospheric zone is called the ozonosphere.

Ques: What is the greenhouse effect?

Ans: The greenhouse effect is the process through which solar energy is absorbed by greenhouse gases instead of being reflected back into space.

Ques: Give examples in which green chemistry has been applied.

Ans: Dry cleaning of clothes, Bleaching of paper, and Synthesising chemicals.

Ques: What is an insecticide?

Ans: Insecticides are chemicals that kill insects.

Ques: The London smog is caused in which season and time of the day?

Ans: The London smog is caused by the hot weather in the summer, especially in the afternoon.

Ques: What is the effect of CFCs on the ozone layer?

Ans: CFCs also known as chlorofluorocarbons tend to damage the ozone layer and create holes in the ozone layer.

Also Read: Chlorofluorocarbons: Classification, Properties and Impacts

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Short Answer Questions [2 marks questions]

Ques: Which substances are responsible for the greenhouse effect? Which disease is caused due to ozone layer depletion?

Ans: The greenhouse effect is caused by the trapping of heat by greenhouse gases such as carbon dioxide, methane, nitrous oxide (N₂O), ozone, and chlorofluorocarbons (CFCs).

Skin cancer is caused when the ozone layer is depleted from the atmosphere. The ultraviolet rays from the sun reach the earth through the holes present in the ozone layer and cause skin related diseases.

Ques: What does the amount of BOD signify?

Ans: BOD in water is a measurement of the quantity of organic material in the water in terms of how much oxygen is required to break it down biologically. Clean water has a BOD value of less than 5 ppm, whereas severely contaminated water has a BOD value of 17 ppm or higher.

Ques: What is smog?

Ans: Smog is a type of air pollution that was named from the combination of smoke and fog in the atmosphere. It is created by a mixture of smoke and sulphur dioxide and occurs when significant amounts of coal are burned in a certain area.

Ques: Define green chemistry.

Ans: The development of chemical products and processes that decreases or eliminates the usage or production of hazardous chemicals is defined as green chemistry. Green chemistry encompasses a chemical product's whole life cycle, including its design, production, usage, and disposal.

Ques: Why is acid rain considered a threat to the Taj Mahal?

Ans: Nitric acid, sulphuric acid, and carbonic acid are some of the harmful acids found in acid rain. When these acids react with the marble of the Taj Mahal, it causes pitting of the monument which has resulted in the monument being slowly eaten away and decolouration of the marble, thus making it lusterless. Thus, acid rain is considered a threat to the Taj Mahal.

Ques: Why does water cover with excessive algal growth become polluted?

Ans: The presence of high algal development indicates that the water contains a lot of phosphate due to fertiliser influx from the surroundings. The decomposition of algae produces a foul odour and an unappealing appearance, making it unsuitable for swimming, boating, and other activities, as well as a fall in dissolved oxygen content, which may be detrimental to aquatic life.

Ques: What are biodegradable and non-biodegradable pollutants?

Ans: Biodegradable pollutants are those that can be degraded by microorganisms, such as leftover vegetables and fruits, sewage, cow dung, etc.

Whereas, Non-biodegradable pollutants are those that cannot be digested by microbes such as mercury, polythene, and aluminium DDT.

Also Read: Effects of Acid Rain

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Long Answer Questions [3 Marks Question]

Ques: Which zone is called the ozonosphere? Give one main reason for ozone depletion. Explain why carbon monoxide is considered to be poisonous.

Ans: The ozonosphere is an area or zone in the stratospheric layer of the atmosphere with a high concentration of ozone gas molecules.

Solvents, spray aerosols, freezers, and air conditioners, among other things, emit ultraviolet radiation. Ultraviolet radiations break down chlorofluorocarbon molecules in the stratosphere, releasing chlorine atoms. Thus, the major cause of ozone layer depletion is chlorofluorocarbons (CFCs).

When carbon monoxide is released into the atmosphere, it is inhaled by animals and humans. Inside the body, carbon monoxide links to haemoglobin to create carboxyl–haemoglobin, which is 300 times more stable than oxygen –haemoglobin. This oxygen deprivation causes headaches, blurred vision, anxiety, and cardiovascular problems. Thus, carbon monoxide is considered to be poisonous.

Ques: Explain how does greenhouse effect cause global warming.

Ans: The greenhouse effect can be defined as the trapping of the sun’s heat in the lower atmosphere as a result of increased pollution-causing chemicals such as carbon dioxide. Water vapour, carbon dioxide (CO₂), methane, nitrous oxides, and chlorofluorocarbons are some of the gases that contribute to the greenhouse effect (CFCs).

The sun’s radiation is partially absorbed by the earth, and the remainder radiation gets reflected back into the atmosphere. The greenhouse gases form a blanket in the atmosphere, trapping radiation and preventing it from leaving. As a result, the earth’s temperature rises, resulting in global warming.

Ques: Explain the following: Mists, Smoke, and Dust.

Ans: Mists: Mists are produced by particles of spray liquids & the condensation of vapours in the air. Examples are portions of herbicides & insecticides, that miss their targets & travel through the air to form mists.

Smoke: They are very small soot particles produced by burning & combustion of organic matter. Oil smoke, Tobacco smoke & Carbon smoke are typical examples.

Dust: It consists of fine particles produced during crushing, grinding & attribution of solid materials. Non-viable dust particulates in the atmosphere consist of ground limestone, sand tailing from floatation, pulverised coal, cement, fly ash & silica dust.

Also Read: Air Pollution: Types, Causes, Effect, Control

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Very Long Answer Questions [5 Marks Question]

Ques. How can you apply green chemistry for the following:

(i) to control photochemical smog.

(ii) to avoid the use of halogenated solvents in drycleaning and that of chlorine in bleaching.

(iii) to reduce the use of synthetic detergents.

(iv) to reduce the consumption of petrol and diesel.

Ans: i) Minimizing the release of nitrogen oxides and hydrocarbons into the atmosphere is the most straightforward strategy to limit or prevent the production of photochemical smog. The following methods can be used to reduce nitrogen oxides and hydrocarbons:

1. The hazardous gases are catalytically transformed into harmless gases by installing efficient catalytic converters in autos.
2. Spraying some compounds into the atmosphere produces free radicals that readily mix with the free radicals that start the reactions, generating deadly photochemical smog compounds. Smog-inhibiting properties have been discovered in the chemical diethyl hydroxylamine.
3. Plants like pinus, juniperus, pyrus, vitis, and others may help metabolise nitrogen oxides.

ii) Dry cleaning solvents are typically chlorinated chemicals, which are carcinogenic. To replace the chlorinated chemicals, suitable detergents that function in liquid carbon dioxide have been developed. H₂O₂ is used instead of Cl₂ to bleach garments in the laundry, which produces superior results and is not toxic. Previously, Cl₂ gas was employed to bleach paper. Chlorine is an extremely harmful substance found in nature. In the presence of a sufficient catalyst, it has been replaced by H₂O₂.

iii) The usage of synthetic detergents as a cleaning agent can be limited to the use of soaps manufactured from vegetable oils. Vegetable oils degrade naturally, whereas detergents do not. Thus, vegetable oils should be prioritised.

iv) CNG (Condensed Natural Gas) and LNG (Liquefied Natural Gas) have been favoured over petrol and diesel since they are pollution-free fuels. Other fuels, such as hydrogen, ethyl alcohol, and so on, can be used instead of gasoline and diesel.

Ques: What measures are necessary to control soil pollution?

Ans: In order to control soil pollution, the following measures are necessary:

1. Use of manures: Manures are semi-decayed organic matter which is added to the soil to maintain its fertility. These are mostly prepared from animal dung & another form of waste. These are much better than the commonly used fertilizers. Manure also helps increase the quality of the soil and the matter grown on it.
2. Use of bio-fertilizers: Biofertilizers usually contain no or less amount of chemicals, thus making them healthier for the soil. There are organisms that are inoculated in bio-fertilizers in order to bring about nutrient enrichment of the soil e.g. nitrogen-fixing bacteria & blue-green algae.
3. Proper sewerage System: Improper management of sewerage can result in many problems. Thus, it is important to install a proper sewerage system. Sewerage recycling plants must be installed in all towns & cities.
4. Salvage & Recycling: Rag-picking removes a large no. of waste articles such s paper, polythene, cardboard rags, empty bottles & metallic articles. These are subjected to recycling & this helps in checking soil pollution.

Ques: On the basis of chemical reactions involved, explain how de chlorofluorocarbons cause thinning of the ozone layer in the stratosphere.

Ans: The major cause of ozone layer depletion is chlorofluorocarbons (CFCs).

Chlorofluorocarbons are broken down by intense UV radiations in the stratosphere, generating chlorine free radical.

CH₂Cl₂(g)Cl(g)+CF₂Cl(g)

The chlorine radical reacts with ozone in the stratosphere to produce chlorine monoxide radicals and molecular oxygen.

Cl(g)+O₃(g)ClO(g)+O₂(g)

More chlorine radicals are produced when a chlorine monoxide radical reacts with atomic oxygen.

ClO(g)+O(g)Cl(g)+O₂(g)

The chlorine radicals are constantly replenished, causing ozone depletion. CFCs are thus transportation agents for the ongoing generation of chlorine radicals in the stratosphere, causing ozone layer damage.

Also Read: Four Spheres of Earth

Ques: Some time ago formation of polar stratospheric clouds was reported over Antarctica. Why were these formed? What happens when such clouds break up by warmth of sunlight?

Ans: Scientists operating in Antarctica have observed ozone layer depletion, or the presence of an ozone hole, over the Antarctic region’s South Pole. Based on the seasons, it was discovered that a unique set of factors was responsible for the ozone hole.

In the summer, nitrogen dioxide and methane react with chlorine monoxide and chlorine atoms to generate chlorine sinks, which prevent ozone depletion, whereas in the winter, polar stratospheric clouds accumulate over Antarctica.

Polar stratospheric clouds occur over Antarctica during the winter season, providing a surface on which chlorine nitrate is hydrolyzed and hypochlorous acid is produced. It also forms molecular chlorine when it interacts with HCl.

ClO + NO₂(g)ClONO₂(g)

Cl(g)+CH₄CH₃(g)+HCl(g)

ClONO₂(g)+H₂OHOCl(g)+HNO₃

ClONO₂(g)+HClCl₂(g)+HNO₃(g)

When the sun comes again in the spring, the warmth of the sun breaks through the cloud, protolyzing HOCl and Cl₂,

HOCl(g) → OH(g) +Cl(g)

Cl₂2Cl(g)

The chlorine radicals that result start the ozone depletion chain reaction.

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