NCERT Solutions for Class 11 Chemistry Chapter 14 Environmental Chemistry

NCERT Solutions for Class 11 Chemistry Chapter 14 – Free PDF Download

*According to the latest update on the CBSE Syllabus 2023-24, this chapter has been removed.

NCERT Solutions for Class 11 Chemistry Chapter 14 Environmental Chemistry are among the most important study materials for the Class 11 examination. Students who wish to score good marks in their board exam must regularly practise the NCERT Solutions for Class 11 Chemistry Chapter 14 Environmental Chemistry. The solutions of Class 11 Chemistry Chapter 14 are prepared by subject experts according to the latest CBSE syllabus.

The NCERT Solutions for Class 11 Chemistry will help students to get a clear idea of the concepts of environmental chemistry. These solutions have answers to the textbook questions, worksheets and exemplary questions that help them get tuned in with the topic. Students can download the PDF of NCERT Solutions for Class 11 to the exercise questions of this chapter from the link below.

Download NCERT Solutions Class 11 Chemistry Chapter 14 PDF

NCERT Solutions for Class 11 Chemistry Chapter 14 Environmental Chemistry

Environmental Chemistry is one of the most important chapters in the NCERT Class 11 Chemistry Book. In this chapter, many important concepts related to the environment are taught to students, like atmospheric pollution, water pollution, soil pollution and reasons for soil pollution. Apart from these, when students refer to NCERT Solutions for Class 11 Chemistry Chapter 14, they will get to know about strategies to control environmental pollution, like waste disposal and the use of pesticides to reduce soil pollution.

Subtopics of Class 11 Chemistry Chapter 14 – Environmental Chemistry

1. Environmental Pollution
2. Atmospheric Pollution
   1. Tropospheric Pollution
   2. Stratospheric Pollution
3. Water Pollution
   1. Causes of Water Pollution
   2. International Standards for Drinking Water
4. Soil Pollution
   1. Pesticides
5. Industrial Waste
6. Strategies to Control Environmental Pollution
   1. Waste Management
   2. Waste Management
7. Green Chemistry
   1. Introduction
   2. Green Chemistry in Day-to-Day Life

Class 11 Chemistry NCERT Solutions (Environmental Chemistry) – Important Questions

Question 14.1:

Define environmental chemistry.

Answer 14.1:

Environmental chemistry refers to the study of biochemical and chemical processes that occur in our nature. It also delves into the reaction, origin, effects and transport of the chemical species on our earth.

Question 14.2:

Explain tropospheric pollution in 100 words.

Answer 14.2:

The presence of unwanted substances in the troposphere’s lowest layer causes tropospheric pollution.

The major pollutants include oxides of nitrogen, sulphur, carbon and hydrocarbons.

• Oxides of nitrogen (NO₂, NO) and sulphur (SO₂ and SO₃) which are formed due to the burning of coal, automobile fuel and other fossil fuels, form nitric acid (HNO₃) and sulphuric acid (H₂SO₄) by reacting with water in the presence of atmospheric oxygen. This results in ‘Acid rain’.

2SO_2(g) + O_2(g) + 2H₂O_(l)

4NO_(g) + O_2(g) + 2H₂O_(l)

Acid rain harms plants, agriculture and trees. It also causes respiratory problems in humans.

• Hydrocarbons are compounds that contain carbon and hydrogen in them. They burn to form oxides of carbon. They are carcinogenic in nature and are also regarded as major pollutants.
• Carbon monoxide (CO) reacts with the haemoglobin in our blood and is poisonous in nature, and can even be fatal. Even though carbon dioxide (CO₂) is not toxic by itself, it contributes to the increase in global warming by trapping extra sun rays. This results in a heating effect on the earth, thus increasing the earth’s temperature.
• Particulates like dust, smoke, fume and mist block our nasal passage and are considered harmful to our health.
• Smog is caused due to the combination of smoke and fog, which reduces the visibility of traffic.

Photochemical smog is formed as a result of the presence of ozone, PAN, acrolein and formaldehyde. It causes headaches, eye irritation and chest pain in humans. It cracks rubber tires and also damages the plants.

 Question 14.3:

Carbon monoxide gas is more dangerous than carbon dioxide gas. Why?

Answer 14.3:

Both carbon dioxide (CO₂) and carbon monoxide (CO) are emitted during the combustion of various fuels. Carbon monoxide is toxic in nature, whereas carbon dioxide is non-poisonous in nature.

Carbon monoxide is deemed toxic since it forms a complex with haemoglobin (carboxyhemoglobin), which is more stable than the oxygen-haemoglobin complex. A range of 3–4% of carboxyhemoglobin can decrease the oxygen-carrying capacity of our blood. This can result in weak eyesight, headaches, cardiovascular disorders and nervousness. A little increase in the above concentration can even be fatal.

Carbon dioxide is harmful only at very high concentrations.

Question 14.4:

List gases which are responsible for the greenhouse effect.

Answer 14.4:

The major gases that cause the greenhouse effect are:

1) Chlorofluorocarbons (CFCs)

2) Methane (CH₄)

3) Carbon dioxide (CO₂)

4) Nitrous oxide (NO)

5) Water (H₂O)

6) Ozone (O₃)

Question 14.5:

Statues and monuments in India are affected by acid rain. How?

Answer 14.5:

Oxides of nitrogen (NO₂, NO) and sulphur (SO₂ and SO₃) which are formed due to the burning of coal, automobile fuel and other fossil fuels, form nitric acid (HNO₃) and sulphuric acid (H₂SO₄) by reacting with water in the presence of atmospheric oxygen. This results in ‘Acid rain’.

2SO_2(g) + O_2(g) + 2H₂O_(l)

4NO_(g) + O_2(g) + 2H₂O_(l)

Acid rain harms plants, agriculture and trees. It also causes respiratory problems in humans.

Acid rain damages buildings and structures made of metal and stone. Limestone is a major constituent used in various monuments and statues like the Taj Mahal in India.

Acid rain, when reacting with limestone, causes loss of colour and lustre of monuments, resulting in their disfiguration.

The reaction is as follows:

CaCO₃ + H₂SO₄ 

Question 14.6:

What is smog? How is classical smog different from photochemical smogs?

Answer 14.6:

Smog is a combination of smoke and fog, which causes air pollution. There are two types of smogs:

a) Photochemical smog

b) Classical smog

They can be differentiated as follows:

Question 14.7:

Write down the reactions involved during the formation of photochemical smog.

Answer 14.7:

Photochemical smog is formed due to the reaction of sunlight with nitrogen oxides and hydrocarbons. Formaldehyde, nitric oxide, ozone, PAN and acrolein are the main components of photochemical smog. The steps involved in the formation of photochemical smog are:

Hydrocarbons and nitrogen dioxide are released into the atmosphere as a result of the burning of fossil fuels. Due to high concentrations of these pollutants, they react with sunlight. The reactions proceed as shown below:

NO₂

(Nitrogen dioxide)            (Nitric oxide)

O          +          O₂  

O₃       +          NO  

Since NO₂ and O₃ are oxidising agents, they react with the unburnt hydrocarbons to produce acrolein, PAN and formaldehyde.

Question 14.8:

What are the harmful effects of photochemical smog, and how can they be controlled?

Answer 14.8:

• Photochemical smog is oxidising in nature since it is composed of NO₂ and O₃, which are responsible for the corrosion of rubber, stones, metals and painted surfaces. Photochemical smog also contains formaldehyde, PAN and acrolein. Both ozone and PAN and cause eye irritation, while nitric oxide (derived from NO₂) is responsible for throat and nose irritation. At higher levels, this type of smog can also cause headaches, throat dryness, chest pain and other respiratory ailments.

CONTROL MEASURES:

Use of catalytic converters can be used to prevent the release of NO₂ into the atmosphere.

Plants such as Pyrus, Pinus, Quercus, Juniparur, and Vitis can be planted, as these have the capability to metabolise NO₂.

Question 14.9:

What are the reactions involved in ozone layer depletion in the stratosphere?

Answer 14.9:

In the stratosphere, ozone is actually formed by the action of UV rays on Dioxygen molecules(O₂).

(i)  O_2(g)  

(ii)  O_2(g) + O_(g) 

The second reaction shows that there is a dynamic equilibrium between the decomposition and production of ozone molecules. Any factor that disturbs this equilibrium may lead to the ozone layer getting depleted due to its decomposition. One such example of these factors is chlorofluorocarbon compounds (CFCs). These are non-flammable and non-reactive molecules that find usage in air conditioners, refrigerators, plastics, and electronic industries.

Once it is released into the atmosphere, these CFCs get mixed with atmospheric gases and then reach the stratosphere, where they get decompose due to reactions with UV radiation.

(iii) CF₂Cl_2(g)

The chlorine-free radical, which is produced in the third reaction, reacts with ozone as shown below:

(iv)

And, Cl

The radicals, on further reaction with atomic oxygen, result in the production of more chlorine radicals.

This regeneration of chlorine-free radicals results in a continuous breakdown of ozone in the stratosphere, thus almost permanently damaging the ozone layer.

Question 14.10:

What do you mean by an ozone hole? What are its consequences?

Answer 14.10:

Stratospheric clouds present in Polar Regions provide a surface for the reaction of hypochlorous acid and chlorine nitrate, which on further reaction, gives molecular chlorine. HOCl and Molecular chlorine get photolysed to provide chlorine-free radicals.

The radicals, in reaction with atomic oxygen, result in the production of more chlorine radicals.

This regeneration of chlorine-free radicals results in a continuous breakdown of ozone in the stratosphere, thus almost permanently damaging the ozone layer.

This phenomenon is known as the ‘ozone hole’.

Effects of ozone layer depletion:

The Earth is shielded from the harmful UV radiation of the sun by the ozone layer. When this layer gets depleted, a greater amount of radiation will enter the earth’s atmosphere. They are deemed harmful since they lead to skin cancer, cataract, ageing of the skin and also cause sunburns. They also prove fatal to phytoplankton, thus resulting in a decline in fish productivity. Excess exposure to these rays may, in some cases, also lead to mutation in plants. The moisture content of the soil decreases with an increase in exposure to UV radiation.

Question 14.11:

What are the major causes of water pollution? Explain.

Answer 14.11:

Water pollution occurs when undesirable and unwanted substances are added to the water bodies, thus choking the aquatic life in those water bodies.

The major sources of water pollutants are as given below:

The major pollutants are:

1. Pathogens: Bacteria and other micro-organisms come under this category. They get into water bodies through domestic sewage and animal excreta. Bacteria like Escherichia coli and Streptococcus faecalis, which are found in human excreta, are known vectors of gastrointestinal diseases.

2. Organic wastes: They are generally bio-degradable wastes that pollute the water bodies by mixing with them during their runoff phase. An excess amount of organic matter in water bodies sucks up the dissolved oxygen in water, thus inhibiting aquatic life in these water bodies.

3. Chemical pollutants: Heavy metals like mercury, cadmium and nickel come under this category. These chemicals, when present above the allowable limit, can result in damage to the central nervous system, kidneys and liver.

Question 14.12:

Have you ever observed any water pollution in your area? What measures would you suggest to control it?

Answer 14.12:

Human activities like stormwater drainage, run-off from agricultural fields, discharges from wastewater treatment plants, etc., result in water pollution.

Toxic metals, like Fe, Al and Mn, are released into water bodies by industries and factories. So, it should be made sure that the water released from these industries is free of this type of toxicity. Their discharges should be frequently checked for traces of these metals and then released into water bodies.

Instead of using fertilisers, manure and compost can be used effectively so that these fertilisers don’t get into water bodies and pollute them.

Question 14.13:

What do you mean by Biochemical Oxygen Demand (BOD)?

Answer 14.13:

Biochemical oxygen demand is the amount of oxygen required by bacteria to decompose organic matter in a certain volume of a sample of water. Clean water will have a BOD of below 5 ppm, whereas a highly polluted water source will have a BOD of more than 17 ppm.

Question 14.14:

Do you observe any soil pollution in your neighbourhood? What efforts will you make to control soil pollution?

Answer 14.14:

Pesticides and fertilisers are the major pollutants that cause soil pollution. When insecticides like DDT are used, they get stuck in the soil for a longer time since they are not soluble in water and thus contaminating the crops and soil. Moreover, pesticides and insecticides are not biodegradable in nature, and when they enter the food chain, they go to the highest trophic levels and thus affect the whole biodiversity of an area.

Thus, soil pollution can be controlled by controlling the addition of pesticides and fertilisers and instead using manures and compost.

Question 14.15:

What are pesticides and herbicides? Explain, giving examples.

Answer 14.15:

A mixture of two or more substances that are used to kill pests is called a Pesticide. Pests that need to be killed are plant pathogens, weeds, insects, molluscs, etc., which affect the plants and lead to their death. Some common pesticides include Dieldrin and Aldrin.

Herbicides are similar to pesticides but are used to kill weeds. Examples include sodium arsenite (Na₃AsO₃) and sodium chlorate (NaClO₃).

Question 14.16:

What do you mean by green chemistry? How will it help decrease environmental pollution?

Answer 14.16:

The production process uses the existing knowledge that we have on the principles of chemistry to create, develop and implement chemical compounds and products to decrease the number of hazardous substances in the environment.

Green chemistry aims to make sure that the end product’s yield is 100% so that there are no harmful substances released into the environment.

For example, we now use H₂O₂ instead of tetrachloroethane and chlorine gas in the process of bleaching and drying paper.

Question 14.17:

What would have happened if the greenhouse gases were totally missing in the earth’s atmosphere? Discuss.

Answer 14.17:

The greenhouse gases that are present in our atmosphere trap the UV rays coming from Sun and heat up the earth.

In the absence of greenhouse gases, the earth won’t be able to retain any heat, which is essential for the survival of most of the species on earth.

Without greenhouse gases, the earth’s average temperature will decline, thus making this planet uninhabitable.

Question 14.18:

A large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping, but you find an abundance of phytoplankton. Suggest a reason for the fish kill.

Answer 14.18:

Phytoplankton is consumed by bacteria which require dissolved oxygen for this process. Thus, the higher the amount of Phytoplankton, the larger the use of dissolved oxygen by bacteria to consume Phytoplankton. Thus, all the oxygen in the lake is used up, and BOD drops below 6 ppm, suffocating the fish.

Question 14.19:

How can domestic waste be used as manure?

Answer 14.19:

Firstly, the waste has to be segregated into biodegradable and non-biodegradable wastes. Those that can be degraded by bacteria, such as leaves and food wastes, are biodegradable and dumped in landfills along with micro-organisms that decompose them. The decomposed matter called Humus can be used as manure. The rest of the wastes, which are non-biodegradable, have to be recycled.

Question 14.20:

For your agricultural field or garden, you have developed a compost-producing pit. Discuss the process in the light of bad odour, flies and recycling of wastes for a good product.

Answer 14.20:

• The compost pit should be covered to prevent bad odour and flies.
• Non-biodegradable wastes should not be dropped into the compost pit so as not to interfere with the decomposition of the wastes. Instead, they should be sent for recycling.

Some of the important topics covered in NCERT Solutions for Class 11 Chemistry Chapter 14

• Atmospheric Pollution
• Water Pollution
• Soil Pollution
• Industrial Waste
• Strategies to Control Environmental Pollution
• Green Chemistry

Students who wish to appear for competitive exams like JEE Mains and NEET examinations after Class 12 should study the chapters of Class 11 and can utilise NCERT Solutions as their primary reference. The topics included in the CBSE Class 11 Chemistry Syllabus are the basics of the topics to be taught in Class 12.

NCERT textbooks are the best study materials for the students of Class 11. Studying the NCERT textbooks will help them to understand the chapters in a better way. Further, students can also utilise NCERT Solutions to understand the key concepts clearly and learn the methods to solve problems correctly.