Text Book Back Questions and Answers - Chapter 15 Environmental Chemistry 11th Chemistry Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]

Updated On May 15, 2024

By SaraNextGen

Chapter 15 Environmental Chemistry

Question 1.
Th gaseous envelope around the earth is known as atmosphere. The region lying between an altitude of 11-50 km is –
(a) Troposphere
(b) Mesophere
(c) Thermosphere
(d) Stratosphere
Answer:
(d) Stratosphere

Question 2.
Which of the following is natural and human disturbance in ecology?
(a) Forest fire
(b) Floods
(c) Acid rain
(d) Greenhouse effect
Answer:
(a) Forest fire

Question 3.
Bhopal Gas Tragedy is a case of –
(a) thermal pollution
(b) air pollution
(c) nuclear pollution
(d) land pollution
Answer:
(b) air pollution

Question 4.
Haemoglobin of the blood forms carboxyhaemoglobin with –
(a) Carbon dioxide
(b) Carbon tetrachioride
(c) Carbon monoxide
(d) Carbonic acid
Answer:
(c) Carbon monoxide

Question 5.
Which sequence for greenhouse gases is based on GWP?
(a) CFC > N₂O > CO₂ > CH₄
(b) CFC > CO₂ > N₂O > CH₄
(c) CFC > N₂O > CH₄ > CO₂
(d) CFC > CH₄ > N₂O > CO₂
Answer:
(c) CFC > N₂O > CH₄ > CO₂

Question 6.
Photo chemical smog formed in congested metropolitan cities mainly consists of –
(a) Ozone, SO₂ and hydrocarbons
(b) Ozone, PAN and NO₂
(c) PAN, smoke and SO₂
(d) Hydrocarbons, SO₂ and CO₂
Answer:
(b) Ozone, PAN and NO₂

Question 7.
The pH of normal rain water is –
(a) 6.5
(b) 7.5
(c) 5.6
(d) 4.6
Answer:
(c) 5.6

Question 8.
Ozone depletion will cause –
(a) forest fires
(b) eutrophication
(c) bio magnification
(d) global warming
Answer:
(d) global warming

Question 9.
Identify the wrong statement in the following.
(a) The clean water would have a BOD value of more than 5 ppm
(b) Greenhouse effect is also called as Global warming
(c) Minute solid particles in air is known as particulate pollutants
(d) Biosphere is the protective blanket of gases surrounding the earth
Answer:
(a) The clean water would have a BOD value of more than 5 ppm

Question 10.
Living in the atmosphere of CO is dangerous because it –
(a) Combines with O₂ present inside to form CO₂
(b) Reduces organic matter of tissues
(c) Combines with haemoglobin and makes it incapable to absorb oxygen
(d) Dries up the blood
Answer:
(c) Combines with haemoglobin and makes it incapable to absorb oxygen

Question 11.
Release of oxides of nitrogen and hydrocarbons into the atmosphere by motor vehicles is prevented by using –
(a) grit hamber
(b) scrubbers
(c) trickling filters
(d) catalytic convertors
Answer:
(c) trickling filters

Question 12.
Biochemical oxygen Demand value less than 5 ppm indicates a water sample to be
(a) highly polluted
(b) poor in dissolved oxygen
(c) rich in dissolved oxygen
(d) low COD
Answer:
(c) rich in dissolved oxygen

Question 13.
Match the list I and list II and select the correct answer using the code given below in the list:

Answer:

Question 14.
Match the list I and list II and select the correct answer using the code given below in the list

Answer:

Question 15.
Assertion (A) : if BOD level of water in a reservoir is more than 5 ppm it is highly polluted.
Reason(R) : High biological oxygen demand means high activity of bacteria in water
(a) (i)
(b) (ii)
(c) (iii)
(d) (iv)
Answer:
(d) (iv)

Question 16.
Assertion (A) : Excessive use of chlorinated pesticide causes soil and water pollution.
Reason (R) : Such pesticides arc non-biodegradable.
(a) (i)
(b) (ii)
(c) (iii)
(d) (iv)
Answer:
(a) (i)

Question 17.
Assertion (A) : Oxygen plays a key role in the troposphere.
Reason (R) : Troposphere is not responsible for all biological activities
(a) (i)
(b) (ii)
(c) (iii)
(d) (iv)
Answer:
(d) (iv)

Short Answer Questions

Question 18.
Dissolved oxygen in water is responsible for aquatic life. What processes are responsible for the reduction in dissolved oxygen in water’?
Answer:

• Organic matter such as leaves, grass, trash can pollute water. Microorganisms present in water can decompose these organic matter and consume dissolved oxygen in water.
• Eutrophication is a process by which water bodies receive excess nutrients that stimulates excessive plant growth. This enhanced plant growth in water bodies is called algal bloom.
• The growth of algae in extreme abundance covers the water surface and reduces the oxygen concentration in water. Thus, bloom-infeded water inhibits the growth of other. living organisms in the water body.
• This process in which the nutrient rich water support a dense plant population, kills animal life by depriving it of oxygen and results in loss of biodiversity is known as eutrophication.

Question 19.
What would happen, if the greenhouse gases were totally missing in the earth’s atmosphere?
Answer:

• The primary greenhouse gases in Earth’s atmosphere are water vapour, carbon dioxide, methane, nitrous oxide and ozone.
• Naturally occurring greenhouse gases allow solar radiations to reach the earth’s surface, while trapping radiations from the earth on its way back out to space.
• There would he no life on Earth without the warmth provided by this natural greenhouse gases.
• In the absence of greenhouse gases. the average temperature of the earth will decrease drastically. As a result. life on Earth would be impossible.

Question 20.
Define smog.
Answer:

• Smog is a combination of smoke and fog which form droplets that remains suspended in the air.
• Smog is a chemical mixture of gases that forms a brownish yellow haze. It mainly consists of ground level ozone, oxides of nitrogen, volatile organic compounds, SO₂, acidic aerosols and some other gases.

Question 21.
Which is considered to be earth’s protective umbrella? Why?
Answer:

• At high altitudes in the atmosphere consists of a layer of ozone (O₂) which acts as an umbrella for harmful UV radiations. Ozone is considered to be earth’s protective umbrella.
• It protects us from harmful effects of UV-radiations of the sun such as skin cancer.
• Ozone layer prevent the UV radiations to reach the earth surface. So it acts as an umbrella for the Earth.

Question 22.
What are bio-degradable and non-biodegradable pollutants?
Answer:

• The pollutants which can be easily decomposed by the natural biological processes are called biodegradable pollutants. For example plant wastes, animal wastes.
• The pollutants which cannot be decomposed by the natural biological processes are called non-biodegradable pollutants. For example, metal wastes such as Hg and Pb, D.D.T. plastics, nuclear vastcs.

Question 23.
From where does ozone come in the photochemical smog?
Answer:

• Photochcrnical smog is formed by the combination of smoke, dust and fog with air pollutants in the presence of sunlight.
• Chemically it is oxidising in nature because of high concentration of oxidising agents such as NO₂ and O₂. So it is also called oxidising smog.
• Photochemical smog is formed by following reactions:
• N₂ + O₂ → 2NO
  2NO + O₂ → 2NO₂
  
  (O) + O₂ → O₃
  O₃ + NO → NO₂ + O₂
• NO and O₃ arc strong oxidizing agents and they can react with unburnt hydrocarbons in polluted air to form formaldehyde, acrolcin and PAN.

Question 24.
A person was using water supplied by corporation. Due to shortage of water he started using underground water. He felt laxative effect. What could be the cause?
Answer:
Drinking water containing moderate level of sulphatcs is harmless. But excessive concentration (>500 ppm) of suiphates in drinking water causes laxative effect.

Question 25.
What is green chemistry?
Answer:

• Green chemistry is a chemical philosophy encouraging the design of products and processes that reduces or eliminates the use and generation of hazardous substances.
• Efforts to control environmental pollution resulted in development of science for the synthesis of chemicals favorable to environment.
• Green chemistry means science of environmentally favorable chemical synthesis.

Question 26.
Explain how does greenhouse effect cause global warming.
Answer:

• The earth’s atmosphere allows most of the visible light from the sun to pass through and reach the earth’s surface. As earth’s surface is heated by sunlight, it radiates a part of this energy back towards the space as longer IR wavelengths.
• Some of the heat is trapped by CH₂, CO₂. CFCs and water vapour present in the atmosphere. They absorb IR radiations and block a large portion of earth’s emitted radiations.
• The radiations thus absorbed is partly remitted to the earth’s surface. Therefore the earth’s surface gets heated up by a phenomenon called greenhouse effect.
• Thus greenhouse effect is defined as the heating up of the earth surface due to trapping of infrared radiations reflected by earth’s surface by CO₂ layer in the atmosphere. The heating up of the earth through the greenhouse effect is called global warming.

Question 27.
Mention the standards prescribed by BIS for quality of drinking water.
Answer:
Standard characteristics prescribed for deciding the quality of drinking water by BIS are as follows:

Question 28.
How does classical smog differ from photochemical smog?
Answer:
Classical smog:

• Classical smog is caused by coal-smoke and fog.
• It occurs in cold humid climate.
• The chemical composition is the mixture of SO₂, SO₃ gases and humidity.
• Chemically it is reducing in nature because of high concentration of SO, and so it is also called reducing smog.
• It is primarily responsible for acid rain.
• It also causes bronchial irritation.

Photochemical smog:

• Photochemical smog is cause by photochemical oxidants.
• It occurs in warm, dry and sunny climate.
• The chemical composition is the mixture of NO₂ and O₃ gases.
• Chemically it is oxidising in nature because of high concentration of oxidising agents such as NO₂ and O₃
• and so it is also called oxidising smog.
• It causes irritation to eyes, skin and lungs and increase the chances of asthma.
• It causes corrosion of metals, stones

Question 29.
What are particulate pollutants? Explain any three.
Answer:
1. Particulate pollutants are small solid particles, and liquid droplets suspended in air.
Examples:
dust, pollen, smoke, soot and liquid aerosols.

2. Types of Particulates:
Particulates in the atmosphere may be of two types:

• viable particulate and
• non-viable particulate.

3.The viable particulates are small size living organisms such as bacteria, fhngi, moulds and algae which are dispersed in air.

4. The non-viable particulates are small solid particles and liquid droplets suspended in air. There are four types of non-viable particulates in the atmosphere. They are
(a) Smoke
(b) Dust
(c) Mist
(d) Fumes

5. Smoke:
Smoke particulate consists of solid particles formed by combustion of organic matter. For example, cigarette smoke, oil smoke, smokes from burning of fossil fuels, garbage and dry leaves.

6. Dust:
It is composed of fine solid particles produced during crushing and grinding of solid materials. For example, sand from sand blasting, saw dust from wood works and fly ash from power generating units.

7. Mist:
They are formed by particles of sprayed liquids and condensation of vapours in air. For example, sulphuric acid mist, herbicides and insecticides sprays can form mists.

8. Fumes:
They are obtained by condensation of vapours released during sublimation, distillation, boiling and calcination and by several other chemical reactions.
For example:
organic solvents, metals and metallic oxides.

Question 30.
Even though the use of pesticides increases the crop production, they adversely affect the living organisms. Explain the function and the adverse effects of the pesticides.
Answer:
1. Pesticides are the chemicals that are used to kill or stop the growth of unwanted organims. But these pesticides can affect the health of human beings. Pesticides are classified as
(a) insecticides,
(b) Fungicides and
(c) Herbicides.

 (a) Insecticides:
Insecticides like DDT, BHC, Aidrin can stay in soil for a long period of time and are absorbed by soil. They contaminate root crops like carrot, radish.

(b) Fungicides:
Organomercury compounds dissociate in soil to produce mercury which is highly toxic.

(c) Herbicides:
They are used to control unwanted plants and are also known as weed killers. Eg, Sodium chlorate, sodium nitrate. They are toxic to mammals.

Question 31.
Ethane bums completely in air to give CO₂. while in a limited supply of air gives CO. The same gases are found in automobile exhaust. Both CO and CO₂ are atmospheric pollutants

1. What is the danger associated with these gases?
2. How do the pollutants affect the human body?

Answer:
Danger associated with CO and CO₂ & health hazards to human body
(a) Carbon monoxide binds with haemoglohin and form carboxyhaemoglobin which impairs normal oxygen transport by blood and hence the oxygen carrying capacity of blood is reduced. This oxygen deficiency results in headache, tension, dizziness, loss of consciousness, blurring of eyesight and cardiac arrest.

(b) Increase in CO₂ level in the atmosphere is responsible for global warming. It causes headache and nausea.

Question 32.
On the basis of chemical reactions involved, explain how do CFC’s cause depletion of ozone layer in stratosphere?
Answer:
(i) The chioro-Iluoro derivatives of methane and ethane are named Freons (CFC’s). They slowly pass from troposphere to stratosphere. They stay for a very longer period of about 50-100 years. In the presence of UV radiations, CFC’s break up into chienne free radicals.

(iii) Chlorine radical is regenrated in the course of the reaction. Due to this continuous attack of Cl free radicals, thinning of ozone layer takes place which leads to the formation of ozone hole.

(iv) Li is estimated that for every reactive chlorine atom generated in the stratosphere 1,00,000 molecules of ozone are depleted.

Question 33.
How is acid rain formed? Explain its effect.
Answer:
1. Rain water has a pli of 5.6 due to the dissolution of CO., into it. Oxides of sulphur and nitrogen in the atmosphere may be absorbed by droplets of water that make up the clouds and get chemically converted into sulphuric acid and nitric acid. Due to this the pH of rain water drops below the level of 5.6. Hence it is called acid rain.

2. Acid rain is a by-product of sulphur and Nitrogen oxides in the atmosphere. Burning of fossil fuels in power stations, furnaces and petrol, diesel in motor engines produce SO₂ and NO₂ gases. They are converted into H₂SO₄ and HNO₃ by the reaction with oxygen and water.

3. 2SO₂ + O₃ + 2H₂O → 2H₂SO₄
4NO₂ + O₂+ 2H₂O → 4HNO₃

Harmful effects of acid rain:
1. Acid rain causes damage to buildings made us of marbles. This attack on marble is termed as stone leprosy.
CaCO₃ + H₂SO₂ CaSO₄ + H₂O + CO₂↑

2. Acid rain affects plant and animal life in aquatic ecosystem.

3. It is harmful For agriculture, as it dissolves in the earth and removes the nutrients needed for the growth of plants.

4. It corrodes water pipes resulting in the leaching of heavy metals such as iron, lead and copper into drinking water which have toxic effects.

5. it causes respiratory ailment in humans and animals.

Question 34.
Differentiate the following:

1. BOD and COD
2. Viable and non-viable particulate pollutants

Answer:
Biochemical oxygen demand (BOD):

• The total amount of oxygen (in milligrams) consumed by microorganisms in decomposing the waste in one litre ut water at 20°C for a period of 5 days is called biochemical oxygen demand (BOD).
• its value is expressed in ppm.
• DOD is used as a measure of degree ofwater pollution.
• BOD is only a measurement of consumed oxygen by microorganims to decompose the organic matter.
  Clean water would have BOD value less than 5 ppm.

Chemical ox gen demand (COD):

• Chemical oxygen demand is defined as the amount of oxygen required by the organic matter in a sample of water for its oxidation by a strong oxidising agent like K₇Cr₂O₇ in acidic medium for a period of 2 hours.
• Its value is expressed in mg / litre.
• COD is a measure of amount of organic compounds in a water sample.
• COD refers to the requirement of dissolved oxygen for both the oxidation of organic and inorganic constituents.
• Clean water would have COD value greater than 250 mg/litre.

2. Viable and non-viable particulate pollutants
Viable pollutants:

• The viable particulates are small size living organisms such as bacteria, fungi. moulds, algae which are dispersed in air.
• They are all organic particulates.
• They contain living organisms.
•  Eg. ftingi, bacteria, algae, moulds. Viable particles are the particles with at least one microorganism affecting the sterility of the product.

Non-viable pollutants:

• The non-viable particulates are small solid particles and liquid droplets suspended in air.
• They are all inorganic particulates.
• They contain non-living organisms.
• Eg. Smoke, dust, mist, fumes.
• Non-viable particles are the particles without microorganisms but act as transporting agent for viable particles.

Question 35.
Explain how oxygen deficiency is caused by carbon monoxide in our blood? Give its effect.
Answer:

1. Carbon monoxide binds with haemoglobin and form carboxy the haemoglobin which impairs normal oxygen transport by blood and hence the oxygen carrying capacity of blood is reduced.
2. This oxygen deficiency results in headache, dizziness, tension, loss of consciousness, blurring of eyesight and cardiac arrest.

Question 36.
What are the various methods you suggest lo protect our environment from pollution?
Answer:
Methods to control environmental pollution:

• Waste management Environmental pollution can be controlled by proper disposal of wastes.
• Recycling A large amount of disposed waste materials can he reused by recycling the waste, thus it reduces the landfill. –
• By substitution of less toxic solvents for highly toxic ones are used in industrial processes.
• By growing more trees.
• By using fuels with lower sulphur content.
• By control measures in vehicle emissions which are adequate.