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NCERT Exemplar Class 11 Chemistry Solutions Chapter 14 Environmental Chemistry

NCERT Exemplar Class 11 Chemistry Solutions Chapter 14 Environmental Chemistry

Edited By Sumit Saini | Updated on Sep 10, 2022 06:11 PM IST

Environmental issues are rampant and need to be addressed immediately without any further delay. Awareness needs to be created among students regarding this. NCERT Exemplar Class 11 Chemistry solutions Chapter 14 include types of pollution and strategies to tackle these. We have often heard terms like environmental conservation, preservation etc. However, Environmental chemistry deals with chemical processes that influence chemical composition and speciation of air, water and soil. The chemical fate, mobility of contaminants etc are included in this chapter. NCERT Exemplar class 11 Chemistry chapter 14 solutions aims to condition students and prepare them to be calculative about the chemical compositions and contaminants freely mobile in the environment.

NCERT exemplar class 11 Chemistry solutions chapter 14: MCQ (Type 1)

Question:1

Which of the following gases is not a greenhouse gas?
(i) CO
(ii) O_{3}
(iii) CH_{4}
(iv)H_{2}O vapour
Answer:

The answer is the option (i) CO
Explanation: Greenhouse gases have a property of not absorbing sunlight near the earth’s surface and not radiating back to the earth, CO shows the same traits; hence it is a greenhouse gas.

Question:2

Photochemical smog occurs in warm, dry and sunny climate. One of the following is not amongst the components of photochemical smog, identify it.
(i) NO_{2}
(ii) O_{3}
(iii) SO_{2}
(iv) Unsaturated hydrocarbon
Answer:

The answer is the option (iii) SO_{2}
Explanation: When NO and hydrocarbons are present in large amounts in the atmosphere in the presence of sunlight in summer, photochemical smog is formed. SO_{2} is not responsible for the formation of photochemical smog.

Question:3

Which of the following statements is not true about classical smog?
(i) Its main components are produced by the action of sunlight on emissions of automobiles and factories.
(ii) Produced in cold and humid climate.
(iii) It contains compounds of reducing nature.
(iv) It contains smoke, fog and sulphur dioxide.
Answer:

The answer is the option (i) Its main components are produced by the action of sunlight on emissions of automobiles and factories.
Explanation: Classical smog occurs in cold, humid climate due to the gases released by automobiles and factories. A mixture of smoke, fog and SO_{2} forms classical among.

Question:4

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 __________.
(i) rich in dissolved oxygen.
(ii) poor in dissolved oxygen.
(iii) highly polluted.
(iv) not suitable for aquatic life.
Answer:

The answer is the option (i) Rich in dissolved oxygen
Explanation: BOD refers to the amount of oxygen consumed by microorganism in water. It the value of BOD is less than 5 ppm, then the water is considered to be pure or rich in dissolved oxygen.

Question:5

Which of the following statements is wrong?
(i) Ozone is not responsible for green house effect.
(ii) Ozone can oxidise sulphur dioxide present in the atmosphere to sulphur trioxide.
(iii) Ozone hole is thinning of ozone layer present in stratosphere.
(iv) Ozone is produced in upper stratosphere by the action of UV rays on oxygen.
Answer:

The answer is the option (i) Ozone is not responsible for the greenhouse effect.
Explanation: The contribution of O_3 to the greenhouse effect is about 8 to 10%. About 75% of solar energy is absorbed by the surface of the earth, and the rest is radiated back to the atmosphere. This heat traps gases like CO_{2}, CH_{4}, O_{3}, CFCs \;and\; H_{2}O present in the atmosphere and adds to the heat of the atmosphere, causing global warming.

Question:6

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
(i) Large number of mosquitoes.
(ii) Increase in the amount of dissolved oxygen.
(iii) Decrease in the amount of dissolved oxygen in water.
(iv) Clogging of gills by mud.
Answer:

The answer is the option (iii) Decrease in the amount of dissolved oxygen in the water.
Explanation: Microorganisms oxidise organic waste in the presence of dissolved oxygen present in water; thus, decreasing the amount of dissolved oxygen present in water.

Question:7

Which of the following statements about photochemical smog is wrong?
(i) It has high concentration of oxidising agents.
(ii) It has low concentration of oxidising agent.
(iii) It can be controlled by controlling the release of NO_{2}, hydrocarbons, ozone etc.
(iv) Plantation of some plants like pinus helps in controlling photochemical smog.
Answer:

The answer is the option (ii) It has a low concentration of oxidising agents.
Explanation: Photochemical smog has a high concentration of oxidants since it comprises of O_{3}, nitric oxide, formaldehyde, peroxyacetyl nitrate & acrolein. Photochemical smog causes serious health issues.

Question:8

The gaseous envelope around the earth is known as atmosphere. The lowest layer of this is extended upto 10 km from sea level, this layer is _________.
(i) Stratosphere
(ii) Troposphere
(iii) Mesosphere
(iv) Hydrosphere
Answer:

The answer is the option (ii) Troposphere
Explanation: It extends up to approx. 10 km of height from sea level, and is the lowest region of the atmosphere, where humans live.

Question:9

Dinitrogen and dioxygen are main constituents of air but these do not react with each other to form oxides of nitrogen because _________.
(i) the reaction is endothermic and requires very high temperature.
(ii) the reaction can be initiated only in presence of a catalyst.
(iii) oxides of nitrogen are unstable.
(iv) N_{2} and O_{2} are unreactive.
Answer:

The answer is the option (i) the reaction is endothermic, and it requires a very high temperature.
Explanation: The dissociation energy of N_{2} is very high due to the presence of a triple bond, and it is very stable; therefore, these gases do not react with each other at room temperature.

Question:10

The pollutants which come directly in the air from sources are called primary pollutants. Primary pollutants are sometimes converted into secondary pollutants. Which of the following belongs to secondary air pollutants?
(i) CO
(ii) Hydrocarbon
(iii) Peroxyacetyl nitrate
(iv) NO
Answer:

The answer is the option (iii) Peroxyacetyl nitrate
Explanation:
Ozone is produced when oxygen atoms combine with O_{2} in the air
O(g) + O_{2}(g) \rightarrow O_{3}(g) ………. (ii)
Now, this O3 reacts with NO to regenerate NO2, viz., a brown gas and contributes to haze at high levels.
NO(g) + O_{3}(g) \rightarrow NO_{2}(g) + O_{2}(g) ………….. (iii)
Ozone is toxic. Chemicals such as formaldehyde, Acrolein and PAN are produced due to the reaction of NO�_{2} and O_{3} with unburnt hydrocarbons in the polluted air.
(Note: NO�_{2} and O_{3} are strong oxidising agents).
3CH_{4} + 2O_{3} \rightarrow 3CH_{2}=O + 3H_{2}O

Question:11

Which of the following statements is correct?
(i) Ozone hole is a hole formed in stratosphere from which ozone oozes out.
(ii) Ozone hole is a hole formed in the troposphere from which ozone oozes out.
(iii) Ozone hole is thinning of ozone layer of stratosphere at some places.
(iv) Ozone hole means vanishing of ozone layer around the earth completely.
Answer:

The answer is the option (iii) Ozone hole is thinning of the ozone layer of the stratosphere at some places.
Explanation: There are some unique situations according to the season which is responsible for the zone hole.
In Summer:NO_{2} and CH_{4} react with Chlorine monoxide and chlorine atoms forming chlorine sinks. It prevents much of the ozone depletion.
In Winter: Polar stratospheric clouds are formed over Antarctic. The following reaction occurs there:
NO+O_{3}\rightarrow NO_{2}+O_{2}
CF_{2}Cl_{2}\overset{h\nu }{\rightarrow}\dot{C}F_{2}Cl+\dot{C}l
\dot{C}l+O_{3}\rightarrow Cl\dot{O}+O_{2}
Cl\dot{O}+O\rightarrow \dot{Cl}+O_{2}
These reactions occur in the stratosphere.

Question:12

Which of the following practices will not come under green chemistry?
(i) If possible, making use of soap made of vegetable oils instead of using synthetic detergents.
(ii) Using H_{2}O_{2} for bleaching purpose instead of using chlorine based bleaching agents.
(iii) Using bicycle for travelling small distances instead of using petrol/ diesel based vehicles.
(iv) Using plastic cans for neatly storing substances.
Answer:

The answer is the option (iv) Using plastic cans for neatly storing substances.
Explanation: Plastic is non-biodegradable and causes pollution. Hence, using plastic cans won’t come under green chemistry.

NCERT Exemplar Class 11 Chemistry Solutions Chapter 14: MCQ (Type 2)

Question:13

Which of the following conditions shows the polluted environment.
(i) pH of rainwater is 5.6.
(ii) amount of carbon dioxide in the atmosphere is 0.03%.
(iii) biochemical oxygen demand 10 ppm.
(iv) eutrophication.
Answer:

The answer is the option (iii) biochemical oxygen demand 10 ppm and (iv) eutrophication
Explanation: Water having BOD less than 5ppm is considered as pure water, whereas water having BOD more than 5 ppm is considered as polluted. Therefore, BOD 10ppm will be highly polluted water.
Eutrophication is the process where the water is nutrient-rich but has a dense population; it kills animal life by depriving it of oxygen and results in loss of biodiversity.

Question:14

Phosphate containing fertilisers cause water pollution. Addition of such compounds in water bodies causes __________.
(i) enhanced growth of algae.
(ii) decrease in amount of dissolved oxygen in water.
(iii) deposition of calcium phosphate.
(iv) increase in fish population.
Answer:

The answer is the option (i) enhanced growth of algae & (ii) decrease in the amount of dissolved oxygen in the water
Explanation: Phosphate enhances algae growth when added in water, and this algae growth covers the water surface and decreases the amount of dissolved oxygen in the water.

Question:15

The acids present in acid rain are _________.
(i) Peroxyacetylnitrate
(ii) H_{2}CO_{3}
(iii) HNO_{3}
(iv) H_{2}SO_{4}
Answer:

The answer is the option (ii) H_{2}CO_{3} (iii) HNO_{3} and (iv) H_{2}SO_{4}
Explanation: The pH of rainwater is 5.6 because of the presence of H+ ions; they are formed by the reaction of CO_{2} present in the atmosphere with rainwater
H_{2}O(l) + CO_{2}(g) \rightarrow H_{2}CO_{3}(aq)
H_{2}CO_{3}(aq) \rightarrow H^{+}(aq) +HCO_{3}(aq)
Acid rain is the one where the pH of rainwater drops below 5.6. Its major contributors are SO_{2} and NO_{2} after reaction and oxidation with rainwater,
2SO_{2}(g) + O_{2}(g) + 2H_{2}O(l) \rightarrow 2H_{2}SO_4(aq)
4NO_{2}(g) + O_{2}(g) + 2H_{2}O(l) \rightarrow 4HNO_{2}^{-}(aq)

Question:16

The consequences of global warming may be _________.
(i) increase in average temperature of the earth
(ii) melting of Himalayan Glaciers.
(iii) increased biochemical oxygen demand.
(iv) eutrophication.
Answer:

The answer is the option (i) increase in the average temperature of the earth and (ii) melting of Himalayan Glaciers
Explanation: We know that the earth absorbed 75% of the solar energy and radiated the rest of it back to the atmosphere. This increases the global temperature and may result in the melting of glaciers and polar ice caps due to which the low-lying areas would be flooded. There will be an increase in infectious diseases like dengue, sleeping sickness, yellow fever, etc.

NCERT Exemplar Class 11 Chemistry Solutions Chapter 14: Short Answer Type

Question:17

Greenhouse effect leads to global warming. Which substances are responsible for greenhouse effect?
Answer:

There are various greenhouse gases out of which some are produced naturally, and some are man-made. Methane is a natural gas which is produced when vegetation is burnt or digested or rotted in the absence of oxygen. Paddy fields, coal mines, fossil fuel and rotten garbage, release large amounts of methane into the atmosphere.
Nitrous oxide occurs in the environment naturally but is increasing due to human activities day-by-day.
CFCs (Chlorofluorocarbons) are man-made and used in ACs. They contribute to greenhouse gases, too.

Question:18

Acid rain is known to contain some acids. Name these acids and where from they come in rain?
Answer:

The pH of rainwater is 5.6 because of the presence of H+ ions; they are formed by the reaction of CO2 present in the atmosphere with rainwater
H_{2}O(l) + CO_{2}(g) \rightarrow H_{2}CO_{3}(aq)
H_{2}CO_{3}(aq) \rightarrow H^{+}(aq) +HCO_{3}(aq)
Acid rain is the one where the pH of rainwater drops below 5.6. Its major contributors are SO_{2} and NO_{2} after reaction and oxidation with rainwater; polluted air contains particulate matter that catalyses the oxidation,
2SO_{2}(g) + O_{2}(g) + 2H_{2}O(l) \rightarrow 2H_{2}SO_{4}(aq)
4NO_{2}(g) + O_{2}(g) + 2H_{2}O(l) \rightarrow 4HNO_{3}^{-}(aq)

Question:19

Ozone is a toxic gas and is a strong oxidising agent even then its presence in the stratosphere is very important. Explain what would happen if ozone from this region is completely removed?
Answer:

The stratosphere consists of Ozone gas which protects us from harmful UV radiations (\lambda = 225 mm) coming from the sun. UV radiations can be harmful to humans and cause melanoma, cataract formation in eyes, genetic mutation, and destruction of crops. It can also cause harm to aquatic plants and animals. The main reason for ozone depletion is the release of chlorofluorocarbons (CFCs) in the atmosphere.
Hence, we can say that although O3 is dangerous for us if it is present in the troposphere but in the stratosphere, it protects us from harmful radiations.

Question:20

Dissolved oxygen in water is very important for aquatic life. What processes are responsible for the reduction of dissolved oxygen in water?
Answer:

The factors responsible for the reduction of dissolved oxygen in water are -
(i) It is said that the bacteria responsible for degrading biodegradable detergent feed on it and can also use up all the dissolved oxygen and grow rapidly.
(ii) The addition of fertilisers containing additives such as phosphates can enhance the growth of algae which may cover up the surface of the water and reduce the concentration of oxygen in the water.

Question:21

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

Answer:

Chlorofluorocarbons break down in the stratosphere by the powerful UV radiations and release free radicals of chlorine,
CF_{2}Cl_{2}(g)\overset{uv}{\rightarrow} \dot{Cl}(g) + \dot{C} F_{2}Cl(g)
This chlorine radical reacts with stratospheric ozone and forms chlorine monoxide radicals and molecular oxygen,
\dot{Cl}(g) + O_{3}(g) \rightarrow Cl\dot{O}(g) + O_{2}(g)
Now chlorine monoxide radical produces with atomic oxygen produces more chlorine radicals.
Cl\dot{O}(g) + O(g) \rightarrow \dot{C}l(g) + O_{2}(g)
Breakdown of ozone is caused by continuous regeneration of chlorine radicals. Therefore, we can say that CFCs are transporting agents who continuously generate chlorine radicals into the stratosphere and cause damage to the ozone layer.

Question:22

What could be the harmful effects of improper management of industrial and domestic solid waste in a city?
Answer:

(i) If domestic waste is not disposed of properly, it may go to sewers and be eaten by cattle, and if they swallow polythene bags, it may result in their death.
(ii) Non-biodegradable waste can choke the sewers.

(iii) Improper disposal of waste is considered as the major cause of environmental pollution.
(iv) Similarly, improper management of industrial waste can lead to air, water, and soil pollution.

Question:24

What are biodegradable and non-biodegradable pollutants?
Answer:

(i) Biodegradables are the pollutants that can be decomposed by bacteria, e.g., cow dung, waste of vegetables and fruits, etc.
(ii) Non-biodegradable pollutants are the one which cannot be decomposed by bacteria, e.g., Mercury, polythene, DDT, etc.

Question:25

What are the sources of dissolved oxygen in water?
Answer:

Dissolved oxygen in the water can be used by microorganisms to oxidise organic matter. It reaches water either through the atmosphere or due to photosynthesis carried out by aquatic plants. During the night, photosynthesis cannot take place due to the absence of sunlight, but the plants continue to respire and decrease the amount of dissolved oxygen present in water. The sources of dissolved oxygen in water are-

  • Mechanical aeration

  • Photosynthesis by many aquatic plants &

  • Direct contact of air with the water surface

Question:26

What is the importance of measuring BOD of a water body?
Answer:

BOD is a measure of the amount of organic material present in water, in terms of how much oxygen it requires to break it down biologically. If the water has a value of BOD less than 5 ppm, it is considered as clean water, whereas highly contaminated water has the value of BOD of 17ppm or more.

Question:27

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

Addition of fertilisers containing phosphate enhances the growth of algae in water which covers the surface of the water causing the foul smell, unattractive appearance, unfit for boating or swimming, as well as decreasing the amount of oxygen in the water which can be harmful to aquatic life.

Question:28

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.
Answer:

In an automobile engine, fossil fuels are burnt at a high temperature which releases oxides of sulphur and nitrogen from the chimney which were experienced by the villagers causing them breathing problems.
Here, dinitrogen and dioxygen combine and produce ample amounts of NO and NO_{2} , as shown below:
N_2(g) + O_{2}(g) \rightarrow 2NO(g) …. (at temperature 1483K)
2NO(g) + O_{2}(g) \rightarrow 2NO_{2}(g)
Combustion of Sulphur containing fossil fuel produces SO_{2}
S + O_{2} \rightarrow SO_{2}(g)

Question:29

Oxidation of Sulphur dioxide into 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 SO_{2} into SO_{3}.
Answer:

Oxidation of sulphur without a catalyser can be remarkably slow; however, polluted air contains particulate matter which catalysis the reaction of SO_{2} to SO_{3}.
2SO_{2}(g) + O_{2}(g) \rightarrow 2SO_{3}(g)
This reaction can also be promoted by hydrogen peroxide or ozone
SO_{2}(g) + O_{3}(g) \rightarrow 2SO_{3}(g) + O_{2}(g)
SO_{2}(g) + H_{2}O_{2}(l) \rightarrow H_{2}SO_{4}(aq)

Question:30

From where does ozone come in the photochemical smog?
Answer:

Nitric oxide and the free oxygen atom is formed by breaking NO_2 by absorbing sunlight
NO_2 (g) \rightarrow NO (g) + O (g)
We know that oxygen atoms are very reactive, and hence, they react with O_{2} to form ozone
O(g) + O_2(g) + M \rightarrow O_{3}(g) + M
M can be the inert gas such as N_{2} or O_{3}, which is produced during smog formation.

Question:31

How is ozone produced in stratosphere?
Answer:

The UV radiations that fall on the ozone layer breaks the oxygen molecule into free oxygen(O) atoms; these free atoms of oxygen then react with molecular oxygen to form ozone.
O_{2} (g) \rightarrow O (g) + O (g)
O (g) + O_{2} (g) \rightarrow O_{3} (g)

Question:32

Ozone is a gas heavier than air. Why does the ozone layer not settle down near the earth?
Answer:

Ozone is a thermodynamically unstable gas and can be decomposed into molecular oxygen; therefore, there exists a dynamic equilibrium between production and decomposition of ozone.
O_2 (g) \rightarrow O (g) + O (g)
O (g) + O_{2} (g) \rightarrow O_{3} (g)

Question:33

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

Some time ago the scientists working in Antarctica reported depletion of the ozone layer, or it can also be said that the presence of an ozone hole was reported over the South Pole on Antarctic region.
It was found that a unique set of conditions was responsible for this ozone hole based on the seasons, viz.,
In summer: NO2 reacts with CH4 to form chlorine monoxide and chlorine atoms forming chlorine sinks, which prevents much ozone depletion.
In winter: Polar stratospheric clouds are formed over Antarctica that provides a surface on which chlorine nitrate formed gets hydrolysed and forms hypochlorous acid. It also reacts with HCl and produces molecular chlorine.
ClO + NO_{2} (g) \rightarrow ClONO_{2}
Cl (g) + CH_{4}\rightarrow CH_{3}(g) + HCl (g)
ClONO_{2} (g) +H_{2}O \rightarrow HOCl (g) + HNO_{3}
ClONO_{2} (g) + HCl \rightarrow Cl_{2} (g) + HNO_{3} (g)

When the sunlight returns there in spring, the warmth of the sun breaks the cloud and protolyzes HOCl and Cl_{2},
HOCl(g)\overset{h\nu }{\rightarrow}\dot{O}H(g)\dot{C}l(g)
Cl_{2}\overset{h\nu }{\rightarrow}2\dot{C}l(g)
Therefore, the chain reaction of ozone depletion initiates with the formation of chlorine radicals.

Question:34

A person was using water supplied by the Municipality. Due to the shortage of water, he started using underground water. He felt a laxative effect. What could be the cause?
Answer:

The laxative effect is caused by drinking water having excessive sulphate (>500 ppm); however, it is harmless at moderate levels.

NCERT Exemplar Class 11 Chemistry Solutions Chapter 14: Matching Type

Question:35

Match the terms given in Column I with the compounds given in Column II.

Column I

Column II

(i) Acid rain

(a) CHCl_{2}-CHF_{2}

(ii) Photochemical smog

(b) CO

(iii) Combination of haemoglobin

(c) CO_{2}

(iv) Depletion of ozone layer

(d) SO_{2}


(e) Unstaturated hydrocarbons

Answer:

(i)\rightarrow (c, d); (ii) \rightarrow (d, e); (iii) \rightarrow (b); (iv) \rightarrow (a)
Explanation:
(i) Acid rain occurs due to the presence of CO_{2}, NO_{2} and SO_{2} present in the atmosphere. They give carbonic acid, nitrous acid and sulphurous acid with water.
(ii) Hydrocarbon (unburnt fuel) and SO_{2} forms photochemical smog.
(iii) CO combines with haemoglobin to form carboxyhaemoglobin and doesn’t allow it to bind with oxygen again.
(iv) CFCs causes the depletion of the ozone layer by fastening the reverse process of formation of an oxygen molecule from ozone.

Question:36

Match the pollutant(s) in Column I with the effect(s) in Column II.

Column I

Column II

(i) Oxides of Sulphur

(a) Global warming

(ii) Nitrogen dioxide

(b) Damage to kidney

(iii) Carbon dioxide

(c) 'Blue baby' syndrome

(iv) Nitrate in drinking water

(d) Respiratory diseases

(v) Lead

(e) Red haze in trafficand congested areas

Answer:

(i) \rightarrow (d); (ii) \rightarrow (e); (iii) \rightarrow (a); (iv) \rightarrow (c); (v) \rightarrow (b)
Explanation:
(i) SO_{2} is poisonous, and even its los concentrations can cause respiratory diseases.
(ii) Oxides of nitrogen cause irritant red haze effect in the traffic and congested places.
(iii) CO_{2}’s increases amounts in the air are responsible for global warming.
(iv) Excess nitrate in drinking water can cause methemoglobinemia, i.e., ‘blue baby’ syndrome.
(v) The maximum limit of lead concentration in drinking water is 50 ppb. Consuming it more than that can cause kidney damage.

Question:37

Match the activity given in Column I with the type of pollution created by it given in Column II.

Column I (Activity)

Column II (Effect)

(i) Releasing gases to the atmosphere after burning waste material containing sulphur.

(a) Water pollution

(ii) Using carbonates as pesticides

(b) Photochemical smog, damage to plant life, corrosion to building material, induce breathing problems, water pollution

(iii) using synthetic detergents for washing clothes

(c) Damaging ozone layer

(iv) Releasing gases produced by automobiles and factories in the atmosphere.

(d) May causes nerve diseases in human.

(v) Using chloroflurocarbon compounds for cleaning computer parts

(e) Classical smog, acid rain, water pollution, induce breathing problems, corrosion of metals.

Answer:

(i) \rightarrow (e); (ii) \rightarrow (d); (iii) \rightarrow (a); (iv) \rightarrow (b); (v) \rightarrow (c)
Explanation:
(i) Acid rain, smog formation, breathing problems, etc. are caused by SO_{2}.
(ii) Carbamates are biodegradable pesticides but can severely nerve toxins and cause harm to humans.
(iii) Synthetic detergent cause water pollution since they are non- biodegradable.
(iv) Gases released from factories can cause photochemical smog formation and cause damage to plants, water life, etc.
(v) CFCs present in the atmosphere are responsible for damaging the ozone layer.

Question:38

Match the pollutants given in Column I with their effects given in Column II.

Column I

Column II

(i) Phosphate fertilizer in water

(a) BOD level water increases

(ii) Methane in air

(b) Acid rain

(iii) Synthetic detergents in water

(c) Global warning

(iv) Nitrogen oxides in air

(d) Eutrophication

Answer:

(i) \rightarrow (a, d); (ii) \rightarrow (c); (iii) \rightarrow (a); (iv) \rightarrow (b)
Explanation: Phosphates enhance the growth of algae in the water, which covers the surface of the water and reduces the concentration of oxygen in the water and thereby increasing the BOD level of water. This causes harm or may even prove fatal to animal life by depriving them of oxygen, and this subsequent loss of biodiversity is known as eutrophication.

NCERT Exemplar Class 11 Chemistry Solutions Chapter 14: Assertion and Reason Type

Question:39

Assertion (A): Greenhouse effect was observed in houses used to grow plants and these are made of green glass.
Reason (R) : Greenhouse name has been given because glass houses are made of green glass.

(i) Both A and R are correct and R is the correct explanation of A.
(ii) Both A and R are correct but R is not the correct explanation of A.
(iii) Both A and R are not correct.
(iv) A is not correct but R is correct.
Answer:

The answer is the option (iii) Both A and R are not correct.
Explanation: In cold places, plants need sunlight to grow; hence, they are kept in glasshouse so that they get the proper amount of sunlight to heat up soil and plants. These warm plants and soil emit infrared radiations which are partially reflected and partially absorbed by the glass.

Question:40

Assertion (A) : The pH of acid rain is less than 5.6.
Reason (R) : Carbon dioxide present in the atmosphere dissolves in rain water and forms carbonic acid.

(i) Both A and R are correct and R is the correct explanation of A.
(ii) Both A and R are correct but R is not the correct explanation of A.
(iii) Both A and R are not correct.
(iv) A is not correct but R is correct.
Answer:

The answer is the option (ii) Both A and R are correct, but r is not the correct explanation of A.
Explanation: Normally, the pH of rainwater is 5.6 due to the presence of H+ ions produced due to the dissolution of CO_2 in rainwater. If the pH drops below 5.6, it is known as acid rain.
H_2O(l) + CO_2(g) \rightarrow H_2CO_3(aq)
H_2CO_3(aq) + H^{+}(aq) \rightarrow HCO_{3}^{-}(aq)

Question:41

Assertion (A) : Photochemical smog is oxidising in nature.
Reason (R) : Photochemical smog contains NO_{2} and O_{3}, which are formed during the sequence of reactions.

(i) Both A and R are correct and R is the correct explanation of A.
(ii) Both A and R are correct but R is not the correct explanation of A.
(iii) Both A and R are not correct.
(iv) A is not correct but R is correct.
Answer:

The answer is the option (i) Both A and R are correct, and R is the correct explanation of A.
Explanation: Photochemical smog is also called oxidising smog since it has high concentrations of oxidising agents. When No and hydrocarbons are built up in sufficiently high levels, a chain reaction occurs from their interaction with sunlight where NO is converted to NO_{2}. This NO_{2} absorbs sunlight and breaks into NO and a free oxygen atom.
NO_{2}(g)\overset{h\nu }{\rightarrow}NO(g)+O(g)
O(g)+O_{2}(g)\rightarrow O_{3}(g)

Question:42

Assertion (A): Carbon dioxide is one of the important greenhouse gases.
Reason (R): It is largely produced by respiratory function of animals and plants.

(i) Both A and R are correct and R is the correct explanation of A.
(ii) Both A and R are correct but R is not the correct explanation of A.
(iii) Both A and R are not correct.
(iv) A is not correct but R is correct.
Answer:

The answer is the option (ii) Both A and R are correct, but R is not the correct explanation of A.
Explanation:
Increased amount of CO_{2} is responsible for global warming. It is removed by plants, and hence the balance is maintained.

Question:43

Assertion (A): Ozone is destroyed by solar radiation in the upper stratosphere.
Reason (R): Thinning of the ozone layer allows excessive UV radiations to reach the surface of the earth.

(i) Both A and R are correct and R is the correct explanation of A.
(ii) Both A and R are correct but R is not the correct explanation of A.
(iii) Both A and R are not correct.
(iv) A is not correct but R is correct.

Answer:

The answer is the option (iv) A is not correct, but R is correct.
Explanation: Ozone is produced in the stratosphere as UV rays act on O_{2} molecules. The major reason for ozone depletion is CFCs. With the depletion of the ozone layer, UV rays filter into the troposphere and cause skin cancer, cataract, sunburn, etc., it also damages fish productivity.

Question:44

Assertion (A): Excessive use of chlorinated synthetic pesticides causes soil and water pollution.
Reason (R): Such pesticides are non-biodegradable.

(i) Both A and R are correct and R is the correct explanation of A.
(ii) Both A and R are correct but R is not the correct explanation of A.
(iii) Both A and R are not correct.
(iv) A is not correct but R is correct
Answer:

The answer is the option (i) Both A and R are correct, and R is the correct explanation of A.
Explanation: Pesticides are basically synthetic toxic chemicals with ecological repercussions. Its repeated use gives rise to pests which are resistant to it. Hence, as insect resistance of DDT increases, other organic pesticides like Aldrin and Aieldrin were introduced. Organic toxins and water-insoluble and non-biodegradable.

Question:45

Assertion (A): If BOD level of water in a reservoir is less than 5 ppm it is highly polluted.
Reason (R): High biological oxygen demand means a low activity of bacteria in water.

(i) Both A and R are correct and R is the correct explanation of A.
(ii) Both A and R are correct but R is not the correct explanation of A.
(iii) Both A and R are not correct.
(iv) A is not correct but R is correct.
Answer:

The answer is the option (iii) Both A and R are not correct.
Explanation: BOD is a measure of the amount of organic material present in water, in terms of how much oxygen it requires to break it down biologically. If the water has a value of BOD less than 5 ppm, it is considered as clean water; however, water pollution increases if the BOD increases.

NCERT Exemplar Class 11 Chemistry Solutions Chapter 14: Long Answer Type

Question:46

How can you apply green chemistry for the following :
(i) to control photochemical smog.
(ii) to avoid use of halogenated solvents in drycleaning and that of chlorine in bleaching.
(iii) to reduce use of synthetic detergents.
(iv) to reduce the consumption of petrol and diesel.

Answer:

(i)
(a) Many techniques are used to reduced photochemical smog. If we reduce the primary precursors like NO2, the secondary precursors will be automatically reduced.
(b) Release of hydrocarbons and NO can be reduced by using catalytic converters in automobiles.
(c) Certain plants like Juniparus, Vitus, etc. can metabolise. No, hence, they should be planted.

(ii) Organic solvents are highly toxic, and hence, they should be used carefully. For bleaching cloth, H_{2}O_{2} is used rather than Cl2, viz. harmful.
(iii) Synthetic detergents are harmful; hence their daily use should be reduced, and instead, soap should be used, which is biodegradable.
(iv) CNG and LNG should be used instead of petrol and diesel oil because CNG and LNG are pollution-free.

Question:47

Green plants use carbon dioxide for photosynthesis and return oxygen to the atmosphere, even then carbon dioxide is considered to be responsible for greenhouse effect. Explain why?
Answer:

CO_{2} increases global warming. It is produced by the burning of fossil fuels; however, plants consume CO_{2} for photosynthesis and in turn, emit oxygen, hence reduce global warming.
CO_{2} is confined to troposphere only and forms about 0.03% by volume in the atmosphere.
But as we know, deforestation and burning of fossil fuels is increasing CO_{2}­ and, hence increasing global warming.

Question:48

Explain how does green house effect cause global warming.
Answer:

The 'greenhouse effect' refers to the warming of climate that results when the atmosphere traps heat radiating from Earth toward space. Certain gases in the atmosphere resemble glass in a greenhouse, allowing sunlight to pass into the 'greenhouse,' but blocking Earth's heat from escaping into space. The gases that contribute to the greenhouse effect include water vapor, carbon dioxide (CO2), methane, nitrous oxides, and chlorofluorocarbons (CFCs).

Question:49

A farmer was using pesticides on his farm. He used the produce of his farm as food for rearing fishes. He was told that fishes were not fit for human consumption because large amount of pesticides had accumulated in the tissues of fishes. Explain how did this happen?
Answer:

Pesticides are synthetic toxic chemicals with ecological repercussions. Mostly organic toxins are non-biodegradable and water-insoluble. They are transferred from the lower tropic level to higher tropic level because they are highly persistent. Over time, the concentration of toxins in higher animals increases and cause serious metabolic and physiological disorders.They enter into food chain and hence possess potential harms for the human consumption.

Question:50

For dry cleaning, in the place of tetrachloroethane, liquefied carbon dioxide with suitable detergent is an alternative solvent. What type of harm to the environment will be prevented by stopping use of tetrachloroethane? Will use of liquefied carbon dioxide with detergent be completely safe from the point of view of pollution? Explain.
Answer:

Tetrachloroethene was used as a solvent for cleaning; it contaminates groundwater and is suspected to be a carcinogen. It is now replaced with liquified CO_2 since it will be less harmful to the groundwater.Nowadays, H_{2}O_{2} is used for bleaching, which gives better results and requires a lesser amount of water.

Also read - NCERT Solutions for Class 11 Chemistry

In order to get access to NCERT Solutions for this chapter you have to go on the official website and use NCERT Exemplar Class 11 Chemistry solutions chapter 14 PDF download. Students who wish to score well should definitely download as it is given in the most precise and concise manner.

Also read - NCERT Solutions for Class 11 Chemistry Chapter 14

Main Topics and Subtopics in NCERT Exemplar Class 11 Chemistry Solutions Chapter 14 Environmental Chemistry

Class 11 Chemistry NCERT Exemplar solutions chapter 14 cover the following topics-

  • Environmental Pollution

  • Atmospheric Pollution

  • Tropospheric Pollution

  • Stratospheric Pollution
  • Water Pollution

  • Causes of Water Pollution

  • International Standards for Drinking Water

  • Soil Pollution

  • Pesticides
  • Industrial Waste

  • Strategies To Control Environmental Pollution

  • Waste Management
  • Waste Management
  • Green Chemistry

  • Introduction

  • Green Chemistry in day-to-day Life

What will students Learn from NCERT Exemplar Class 11 Chemistry Solutions Chapter 14?

Our planet is facing innumerable environmental problems and hence addressing these concerns becomes even more critical. Our apathy towards the environment stems out of ignorance. Keeping this view in mind, NCERT Exemplar solutions for Class 11 Chemistry chapter 14 Environmental Chemistry tries to enlighten students about environmental, air, water, soil pollution due to the chemical contribution at different levels of production. In addition to this, the chapter also provides methods of waste disposal and reduction.

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NCERT Exemplar Class 11 Chemistry Solutions Chapter-Wise

Important Topics To Cover For Exams From NCERT Exemplar Class 11 Chemistry Solutions Chapter 14 Environmental Chemistry

The chapter is very simple as it includes topics that you have studied previously. However, along with these basic concepts, there are other terms that you might be unaware of. Let’s have a look at important topics in NCERT Exemplar Class 11 Chemistry solutions chapter 14:

· Atmospheric pollution is a term we all are acquainted with. However, within atmospheric pollution, there is Tropospheric Pollution, Stratospheric Pollution which is something new and will be dealt with in this chapter.

· We live in cities where we are completely detached to soil and have zero idea about its requirements. NCERT Exemplar Class 11 Chemistry chapter 14 solutions throws light on this area. Use of pesticides, fertilizers etc and its aftermath is included.

· Water pollution and industrial waste are co-related. The make in India program is a good initiative if the waste disposal from the industries is prioritized before giving green signals to these industries.

· The only way to tackle the problem of pollution is to address it and realize the need of the time. Management of waste is a great solution to this problem and is looked at in this chapter

· Ever heard the word Green Chemistry? Sustainable chemistry or green chemistry focuses on production of substances that will minimize chemical disruption of the environment or rather of the ecosystem.

Check Chapter Wise NCERT Class 11 Chemistry Solutions

Chapter-1 - Some Basic Concepts of Chemistry

Chapter-2 - Structure of Atom

Chapter-3 - Classification of Elements and Periodicity in Properties

Chapter-4 - Chemical Bonding and Molecular Structure

Chapter-5 - States of Matter

Chapter-6 - Thermodynamics

Chapter-7 - Equilibrium

Chapter-8 - Redox Reaction

Chapter-9 - Hydrogen

Chapter-10 - The S-Block Elements

Chapter-11 - The P-Block Elements

Chapter-12 - Organic chemistry- some basic principles and techniques

Chapter-14 - Hydrocarbons

Chapter-15 - Environmental Chemistry

NCERT Exemplar Class 11 Solutions

Read more NCERT Solution subject wise -

Also, read NCERT Notes subject wise -

Also Check NCERT Books and NCERT Syllabus here:

Frequently Asked Question (FAQs)

1. Why is it important to study this chapter?

This chapter is important not only from the examination point of view but also in order to be a responsible citizen. It is high time students take charge and solve this issue.


2. What are the important topics that a student must cover in NCERT Exemplar Class 11 Chemistry solutions Chapter 14 Environmental Chemistry?

International Standards for Drinking Water, Atmospheric Pollution, Tropospheric Pollution, Stratospheric Pollution, Soil Pollution and Waste management are important topics covered.

3. How many questions are solved in this chapter?

20 questions are solved in all in the Class 11 Chemistry NCERT Exemplar solutions chapter 14.

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A block of mass 0.50 kg is moving with a speed of 2.00 ms-1 on a smooth surface. It strikes another mass of 1.00 kg and then they move together as a single body. The energy loss during the collision is

Option 1)

0.34\; J

Option 2)

0.16\; J

Option 3)

1.00\; J

Option 4)

0.67\; J

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 1000 times.  Assume that the potential energy lost each time he lowers the mass is dissipated.  How much fat will he use up considering the work done only when the weight is lifted up ?  Fat supplies 3.8×107 J of energy per kg which is converted to mechanical energy with a 20% efficiency rate.  Take g = 9.8 ms−2 :

Option 1)

2.45×10−3 kg

Option 2)

 6.45×10−3 kg

Option 3)

 9.89×10−3 kg

Option 4)

12.89×10−3 kg

 

An athlete in the olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

Option 1)

2,000 \; J - 5,000\; J

Option 2)

200 \, \, J - 500 \, \, J

Option 3)

2\times 10^{5}J-3\times 10^{5}J

Option 4)

20,000 \, \, J - 50,000 \, \, J

A particle is projected at 600   to the horizontal with a kinetic energy K. The kinetic energy at the highest point

Option 1)

K/2\,

Option 2)

\; K\;

Option 3)

zero\;

Option 4)

K/4

In the reaction,

2Al_{(s)}+6HCL_{(aq)}\rightarrow 2Al^{3+}\, _{(aq)}+6Cl^{-}\, _{(aq)}+3H_{2(g)}

Option 1)

11.2\, L\, H_{2(g)}  at STP  is produced for every mole HCL_{(aq)}  consumed

Option 2)

6L\, HCl_{(aq)}  is consumed for ever 3L\, H_{2(g)}      produced

Option 3)

33.6 L\, H_{2(g)} is produced regardless of temperature and pressure for every mole Al that reacts

Option 4)

67.2\, L\, H_{2(g)} at STP is produced for every mole Al that reacts .

How many moles of magnesium phosphate, Mg_{3}(PO_{4})_{2} will contain 0.25 mole of oxygen atoms?

Option 1)

0.02

Option 2)

3.125 × 10-2

Option 3)

1.25 × 10-2

Option 4)

2.5 × 10-2

If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will

Option 1)

decrease twice

Option 2)

increase two fold

Option 3)

remain unchanged

Option 4)

be a function of the molecular mass of the substance.

With increase of temperature, which of these changes?

Option 1)

Molality

Option 2)

Weight fraction of solute

Option 3)

Fraction of solute present in water

Option 4)

Mole fraction.

Number of atoms in 558.5 gram Fe (at. wt.of Fe = 55.85 g mol-1) is

Option 1)

twice that in 60 g carbon

Option 2)

6.023 × 1022

Option 3)

half that in 8 g He

Option 4)

558.5 × 6.023 × 1023

A pulley of radius 2 m is rotated about its axis by a force F = (20t - 5t2) newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kg m2 , the number of rotations made by the pulley before its direction of motion if reversed, is

Option 1)

less than 3

Option 2)

more than 3 but less than 6

Option 3)

more than 6 but less than 9

Option 4)

more than 9

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