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

Very Short Answer Questions                                                             (1 Mark)

1. What is the troposphere?

Ans: The troposphere is the lowest layer of the atmosphere, where humans and other creatures live. It reaches a height of approximately $10$ kilometres above sea level.

2. Name some gaseous air pollutants.

Ans: Sulfur, nitrogen, and carbon oxides, hydrogen sulphide, hydrocarbons, ozone, and other oxidants are examples of gaseous air pollution. 

3. What are the diseases caused by sulphur dioxide?

Ans: In humans, sulphur dioxide causes respiratory disorders such as asthma, bronchitis, and emphysema. In addition, sulphur dioxide causes eye irritation, resulting in tears and redness.

4. List gases that are responsible for the greenhouse effect?

Ans: The gases responsible for the greenhouse effect are: carbon dioxide,    methane,    water vapours,    nitrous oxide,    CFC’s.

5. What is the effect of CFC’s on the ozone layer?

Ans: CFC’s also known as chlorofluorocarbons tend to damage the ozone layer and creates holes in the ozone layer.

6. 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. This keeps the earth's surface warm and prevents it from freezing.

7. Which disease is caused due to ozone layer depletion?

Ans: 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.

8. What is smog?

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

9. 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.

10. Name two gases that form acid rain.

Ans: Acid rain is caused by the oxides of sulphur and nitrogen and the gases involved in it are sulphur dioxide \[{\text{(S}}{{\text{O}}_{\text{2}}}{\text{)}}\] and nitrogen dioxide ${\text{(N}}{{\text{O}}_{\text{2}}})$.

11. Which acid is present in acid rain?

Ans: When nitrous oxides, chlorine, or sulphurous gas are released into the atmosphere and react with water from acid rain, they form nitric acid ${\text{(HN}}{{\text{O}}_{\text{3}}}{\text{)}}$ , hydrochloric acid ${\text{(HCl)}}$ , or sulphuric acid ${\text{(}}{{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}{\text{)}}$, respectively.

12. What is PAN?

Ans: PAN is peroxyacetyl nitrate, also known as peroxyacetyl nitrate. It's a pollutant found in photochemical smog as a secondary pollutant. It decomposes into peroxy ethanoyl radicals and nitrogen dioxide gas when exposed to heat. It decomposes into peroxy ethanoyl radicals and nitrogen dioxide gas when exposed to heat.

13. When does rainwater become acid rain?

Ans: Acid rain is defined as rain and other types of precipitation with a pH less than 6.0. It is triggered by the large-scale emission of acidic gases into the atmosphere by thermal power plants, industry, and vehicles.

14. What is BOD?

Ans: The amount of dissolved oxygen required by aerobic biological organisms to break down organic material present in a given water sample at a given temperature over a certain time period is known as biochemical oxygen demand (BOD).

15. 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.

16. What are pesticides?

Ans: The term "pesticide" refers to a chemical (or mixture) that either kills a pest or prevents or lessens the damage that a pest can do. Insects, mice, and other animals, as well as undesirable plants (weeds), fungus, germs, and viruses, can all be pests.

17. What should be the pH of drinking water?

Ans: The pH of the clean drinking water must be between $6.5 - 8.5$.

18. What is the desirable concentration of fluoride ion $({{\text{F}}^ - })$ in drinking water?

Ans: PHS recommends a fluoride content of ${\text{0}}{\text{.7 mg/L}}$ (parts per million (ppm)) for community water systems that add fluoride to their water that decreases the risk of dental fluorosis.

18. What is an insecticide?

Ans: Insecticides are chemicals that kill insects. Ovicides and larvicides are insecticides that are used to kill insect eggs and larvae. Agriculture, medicine, industry, and consumers all utilise insecticides.

19. Name two air pollutants that form photochemical smog.

Ans: Secondary pollutants are formed when two major primary pollutants, nitrogen oxides and volatile organic compounds (VOCs), react with sunlight in a series of chemical processes. The ozone that accumulates at ground level is the secondary pollutant that causes the most worry.

20. What is the effect of excess of ${\text{S}}{{\text{O}}_{\text{4}}}^{2 - }$ ion in drinking water?

Ans: The concentration of sulphate ion i.e. above ${\text{500 ppm}}$ causes a laxative effect. 

Short Answer Type Questions                                                             (2 Mark)       

1. What is the role of the ozone layer in the stratosphere?

Ans: The existence of ozone in the stratosphere blocks 99.5 per cent of the sun's damaging ultraviolet (UV) light from reaching the earth's surface, shielding people and other animals from its destructive effects.

2. What includes stratospheric pollutants? Give examples.

Ans: The outcome of stratospheric pollution is the depletion of the ozone layer in the stratosphere, which allows dangerous ultraviolet light to reach the earth. This depletion is caused by the existence of chlorofluorocarbons in the environment.

3. Why is carbon monoxide considered to be poisonous?

Ans: 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.

4. What are the ill effects of hydrocarbons?

Ans: Hydrocarbons are carcinogenic i.e;    they cause cancer. Plants are harmed by them because they cause ageing, tissue degradation, and the dropping of leaves, flowers, and trigs.

5. Give one main reason for ozone depletion?

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

6. Which zone is called the ozonosphere?

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

7. What is the ‘greenhouse effect’? How does it affect the global climate?

Ans: The greenhouse effect is the warming of the planet or global warming caused by the re-emission of sun's energy collected by the earth, absorption by ${\text{C}}{{\text{O}}_{\text{2}}}$  molecules and ${{\text{H}}_{\text{2}}}{\text{O}}$  vapours existing in the atmosphere near the earth's surface, and then radiation back to the ground. Greenhouse affects the climate. If the pace at which solar radiation reaches the earth continues, the entire global climate will alter dramatically.

8. How can photochemical smog be controlled?

Ans: The photochemical smog will be decreased automatically if we manage the major precursors of photochemical smog, such as ${\text{N}}{{\text{O}}_{\text{2}}}$  and hydrocarbons, as well as the secondary precursors, such as ozone and PAN. In most autos, catalytic converters are employed to prevent the release of nitrogen oxide and hydrocarbons into the atmosphere.

9. What is the composition of photochemical smog?

Ans: Photochemical smog is created when nitrogen oxides and hydrocarbons react photochemically (i.e. in the presence of sunlight).

10. 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 ${\text{5 ppm}}$, whereas severely contaminated water has a BOD value of ${\text{17 ppm}}$  or higher.

11. What is Pneumoconiosis?

Ans: Pneumoconiosis is a type of interstitial lung disease caused by inhaling particular types of dust particles that cause lung damage. Pneumoconiosis is referred to be an occupational lung illness since you're more likely to come into contact with this dust at work.

Short Answer Type Questions                                                             (3 Mark)

1. What are the harmful effects of oxides of nitrogen in the atmosphere?

Ans: The harmful effects are as follows:

1. Plants are harmed by high ${\text{N}}{{\text{O}}_{\text{2}}}$  levels in the atmosphere, which cause leaf spotting, photosynthetic activity to be slowed, and vegetative development to be suppressed.

2. Nitrogen dioxide causes bronchitis in humans and causes respiratory difficulties. It causes acid rain and produces photochemical smog.

3. Nitrogen oxides are damaging to nylon, rayon, and cotton fibres, as well as causing rubber fractures.

4. They also react with ozone (\[{{\text{O}}_{\text{2}}}\]) in the atmosphere, lowering the density of ozone.

2. What are the reactions involved in ozone layer depletion in the atmosphere?

Ans: The reactions are:

1. CFCs are discharged into the atmosphere and combine with other gases before reaching the stratosphere, where UV light decomposes them. ${\text{C}}{{\text{F}}_{\text{2}}}{\text{C}}{{\text{l}}_{\text{2}}}{\text{(g)}}\xrightarrow{{{\text{UV}}}}{\text{C}}{{\text{l}}^{{ \bullet }}}{\text{(g)  +  C}}{{\text{F}}_{\text{2}}}{\text{Cl(g)}}$ 

2. The chlorine free radical produced in the first step reacts with the ozone as: ${\text{C}}{{\text{l}}^{{ \bullet }}}{\text{(g)  +  }}{{\text{O}}_{\text{3}}}{\text{(g)}} \to {\text{Cl}}{{\text{O}}^{{ \bullet }}}{\text{(g)  +  }}{{\text{O}}_{\text{2}}}{\text{(g)}}$ 

3. The chlorine free radicals further reacts with atomic oxygen to produce more chlorine free radicals as: ${\text{Cl}}{{\text{O}}^{{ \bullet }}}{\text{(g)  +  [O]}} \to {\text{C}}{{\text{l}}^{{ \bullet }}}{\text{(g)  +  }}{{\text{O}}_{\text{2}}}{\text{(g)}}$ 

3. Why does rainwater normally have a pH of about$5.6$? When does it become acid rain?

Ans: Rainwater has a pH of $5.6$ due to the production of ${{\text{H}}^{\text{ + }}}$  ions as a result of the interaction of rainwater with ${\text{C}}{{\text{O}}_{\text{2}}}$  in the atmosphere.

${{\text{H}}_{\text{2}}}{\text{O  +  C}}{{\text{O}}_2} \to {\text{2}}{{\text{H}}^{\text{ + }}}{\text{ +  C}}{{\text{O}}_3}^{2 - }$ 

When the value of pH drops below $5.6$, it becomes acidic. Acid rain is also caused by the presence of sulphur and nitrogen oxides in the atmosphere.

$\text{2S}{{\text{O}}_{2}}\text{ + }\!\!~\!\!\text{  }{{\text{O}}_{2}}\text{ + }\!\!~\!\!\text{  2}{{\text{H}}_{2}}\text{O}\to 2{{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{ }\!\!~\!\!\text{ }$

$\text{4N}{{\text{O}}_{\text{2}}}\text{ + }\!\!~\!\!\text{  }{{\text{O}}_{\text{2}}}\text{ + }\!\!~\!\!\text{  2}{{\text{H}}_{\text{2}}}\text{O}\to 4\text{HN}{{\text{O}}_{3}}$

4. Discuss the water pollution caused by industrial water?

Ans: Lead, mercury, cadmium, nickel, cobalt, zinc, and other chemical compounds produced in industrial units contaminate water to a great amount and are linked to a variety of diseases. Mercury toxicity causes minimata disease, while lead poisoning causes a variety of abnormalities. Furthermore, these chemicals contribute to the soil and have a negative impact on plant development and the entire soil biotic system. Both groundwater and water bodies are polluted due to chemical reactions known as leaching.

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