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Chapter: 11th Chemistry : UNIT 15 : Environmental Chemistry

Brief questions and answers: Chemistry: Environmental Chemistry

Brief questions and answers, Answer the following questions : Chemistry: Environmental Chemistry

Environmental Chemistry

Answer the following questions

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

● Micro organisms present in water decompose organic matter like leaves, grass, trass, phytoplankton and consume dissolved oxygen in water.

● Algae bloom


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

● If the green house gases are totally missing from earth's atmosphere, then the earth's average surface temperature would be only about (−18°C) (0°F).

● Plants cannot carry out photosynthesis if CO2 is not present. Human beings cannot survive without plants. So, no life on Earth. 


20. Define smog.

● Smog is a combination of smoke and fog which forms droplets that remain suspended in the air.

● Smog is a chemical mixture of gases that forms a brownish yellow haze over urban cities.

● Smog mainly consists of ground level ozone, oxides of nitrogen, volatile organic compounds, SO2, acidic aerosols and gases and particulate matter.


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

● Earth's protective umbrella- Ozone

● At high altitudes to the atmosphere consists of a layer of ozone (O3) which acts as an umbrella or sheild for harmful UV radiations.

● It protects us from harmful effect such as skin cancer. UV radiation can convert molecular oxygen into ozone as shown in the following reaction.

O2(g) _ uv_→ O(g) + O(g)

O(g) O2(g) _ uv_→ O3(g)

● Ozone gas is thermodynamically unstable and readily decomposes too molecular oxygen.


22. What are degradable and non-degradable pollutants?

i. Bio-degradable pollutants:

● The pollutants which can be easily decomposed by the natural biological processes are called bio-degradable pollutants.

Examples: Plant wastes, animal wastes etc.

ii. Non bio-degradable pollutants:

● The pollutants which cannot be decomposed by the natural biological processes are called Non bio-degradable pollutants.

Examples: metal wastes (mainly Hg and Pb), D.D.T, plastics, nuclear wastes etc.,

● These pollutants are harmful to living organisms even in low concentration.

● As they are not degraded naturally, it is difficult to eliminate them from our environment.


23. From where does ozone come in the photo chemical smog?

● Photochemical smog is the combination of smoke, dust and fog with air pollutants like oxides of nitrogen and hydrocarbons in the presence of sunlight.

● It forms when the sun shines and becomes worse in the afternoon.

● Chemically it is oxidizing in nature because of high concentration of oxidizing agents NO2 and O3, so it is also calles as oxidizing smog. Photochemical smog is formed through sequence of following reactions.

N2 + O2 → 2NO

2NO + O2 → 2NO2

NO2 _sunlight_→ NO + (O)

(O) + O2 → O3


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?

● Excessive concentration (>500ppm) of sulphates in underground drinking water could be the cause for laxative effect. (or)

● Excessive concentration (>500ppm) of sulphates in underground water could be the cause for laxative effect.


25. What is green chemistry?

Efforts to control environmental pollution resulted in development of science for synthesis of chemicals favorable to environment which is called green chemistry. Green chemistry means science of environmentally favorable chemical synthesis. 


26. Explain how does greenhouse effect cause global warming

● The term “ Greenhouse Effect" is used for trapping of heat in the atmosphere by certain gases.

● The earth's atmosphere allows most of the visible light from the sun to pass through and reach Earth's surface.

● As Earth's surface is heated by sunlight, it radiates part of this energy back toward space as longer wavelengths (IR).

● Some of the heat is trapped by CH4, CO2, CFCs and water vapour present in the atmosphere.

● They absorb IR radiation and effectively block a large portion of earth's emitted radiation.

● The radiation thus absorbed is partly reemitted to earth's surface. Therefore, the earth's surface gets heated up by a phenomenon called green house effect.

● Thus green house effect may be 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 earth through the greenhouse effect is called global warming.


27. Mention the standards prescribed by BIS for quality of drinking water

Standard characteristics of drinking water

Characteristics and Desirable limit

I. Physico-chemical characteristics

i) PH : 6.5 to 8.5

ii) Total Dissolved Salts (TDS) : 500 ppm

iii) Total Hardness as (CaCO3) : 300 ppm

iv) Nitrate : 45 ppm

v) Chloride : 250 ppm

vi) Sulphate : 200 ppm

vii) Fluoride : 1 ppm

II. Biological Characteristics

i) Escherichia Coli (E.Coli) : Not at all

ii) Coliforms : Not to exceed 10 (In 100 ml water sample)


28. How does classical smog differ from photochemical smog?


1. Mixture of SO2, SO3, moisture, coal, smoke and fog.

2. Occurs in cool humid climate.

3: Mainly due to the induced oxidation of SO2, to SO3 which reacts with water yielding sulphuric acid.

4. It is also called as reducing smog.

5. Effects: Acid rain, poor visibility affects air and road transport, causes bronchial irritation


1. Mixture of smoke, dust and fog with NO2, NO (in sunlight).

2. occurs in warm,dry and sunny climate.

3. NO and O3 are strong oxidising agents can give formaldehyde, PAN, acrolein.

4. It is called as oxidizing smog.

5. Effects: irritation of eyes, skin and lungs. Increase the chances of asthma. chest pain, corrosion of metal stones, building materials, painted surface.


29. What are particulate pollutants? Explain any three.

Particulate pollutants are small solid particles and liquid droplets suspended in air. Many of particulate pollutants are hazardous. Examples: dust, pollen, smoke, soot and liquid droplets (aerosols) etc,.

i) Smoke:

Smoke particulate consists of solid particles (or) mixture of solid and liquid particles formed by combustion of organic matter.

For example : cigarette smoke, oil smoke, smokes from burning of fossil fuel, garbage and dry leaves.

ii) Dust:

Dust composed of fine solid particles produced during crushing and grinding of solid materials.

For example, sand from sand blasting, saw dust from wood works, cement dust from cement factories and fly ash from powder generating units.

iii) Mists:

They are formed by particles of spray liquids and condensation of vapours in air.

For example, sulphuric acid mist, herbicides and insecticides sprays can form mists.

iv) Fumes:

Fumes are obtained by condensation of vapours released during sublimation, distillation, boiling, calcination and by several other chemical reactions.

For example, organic solvents, metals and metallic oxides form fume particles.

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.


Pesticides are the chemicals that are used to kill or stop the growth of unwanted organisms. But these pesticides can affect the health of human beings.

These are further classified as

a. Insecticides:

Insecticides like DDT, BHC, aldrin etc. can stay in soil for long period of time and are absorbed by soil. They contaminate root crops like carrot, raddish, etc.

b. Fungicide:

Organo mercury compounds are used as most common fungicide. They dissociate in soil to produce mercury which is highly toxic.

c. Herbicides:

Herbicides are the chemical compounds used to control unwanted plants. They are otherwise known as weed killers.

Example: sodium chlorate(NaClO3) and sodium arsenite (Na3 As O3). Most of the herbicides are toxic to mammals.


31. Ethane burns 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

i. What is the danger associated with these gases

ii. How do the pollutants affect the human body?

i) Carbon Monoxide:

● Carbon monoxide is a poisonous gas produced as a result of incomplete combustion of coal are firewood.

● It is released into the air mainly by automobile exhaust.

● It binds with haemoglobin and form carboxy haemoglobin which impairs normal oxygen transport by blood and hence the oxygen carrying capacity of blood is reduced.

● This oxygen deficiency results in headache, dizziness, tension, loss of consciousness, blurring of eye sight and cardiac arrest.

ii) Carbon dioxide:

● Carbon dioxide is released into the atmosphere mainly by the process of respiration, burning of fossil fuels, forest fire, decomposition of limestone in cement industry etc.

● Green plants can convert CO2 gas in the atmosphere into carbohydrate and oxygen through a process called photosynthesis.

● The increased CO2 level in the atmosphere is responsible for global warming. It causes headache and nausea.


32. On the basis of chemical reactions involved, explain how do CFC’s cause depletion of ozone layer in stratosphere?

● The chloro fluoro derivatives of methane and ethane are referred by trade name Freons. These Chloro Fluoro Carbon compounds are stable, non-toxic, noncorrosive and non- inflammable, easily liquefiable and are used in refrigerators, air- conditioners and in the production of plastic foams.

● CFC's are the exhaust of supersonic air craft's and jumbo jets flying in the upper atmosphere. They slowly pass from troposphere to stratosphere.

● They stay for very longer period of 50 −100 years. In the presence of uv radiation, CFC's break up into chlorine free radical

CF2 Cl2 __hv_→  CF2 Cl + Cl

CFCl3  __hv_CF Cl2 + Cl

Cl + O3 → ClO+ O2

ClO+ O → Cl+ O2

● Chlorine radical is regenerated in the course of reaction. Due to this continuous attack of Cl thinning of ozone layer takes place which leads to formation of ozone hole.

● It is estimated that for every reactive chlorine atom generated in the stratosphere 1,00,000 molecules of ozone are depleted.


33.How is acid rain formed? Explain its effect

● Rain water normally has a pH of 5.6 due to dissolution of atmospheric CO2 into it. Oxides of sulphur and nitrogen in the atmosphere may be absorbed by droplets of water that make up clouds and get chemically converted into sulphuric acid and nitric acid respectively as a results of pH of rain water drops to the level 5.6, hence it is called acid rain.

● Acid rain is a by-product of a variety of sulphur and nitrogen oxides in the atmosphere. Burning of fossil fuels (coal and oil) in power stations, furnaces, and petrol, diesel in motor engines produce sulphur dioxide and nitrogen oxides. The main contributors of acid rain are SO2 and NO2. They are converted into sulphuric acid and nitric acid respectively by the reaction with oxygen and water.

2SO2 + O2 + 2H2O → 2H2SO4

4NO2 + O2 + 2H2O → 4HNO3

Harmful effects of acid rain:

Some harmful effects are discussed below:

i) Acid rain causes extensive damage to buildings and structural materials of marbles. This attack on marble is termed as Stone leprosy.

CaCO3 + H2SO4 → CaSO4 + H2O + CO2

ii) Acid rain affects plants and animal life in aquatic ecosystem.

iii) It is harmful for agriculture, trees and plants as it dissolves and removes the nutrients needed for their growth.

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

v) It causes respiratory ailment in humans and animals.


34. Differentiate the following

i. BOD and COD

ii. Viable and non-viable particulate pollutants

i) Biochemical oxygen demand (BOD):

The total amount of oxygen in milligrams consumed by microorganisms in decomposing the waste in one liter of water at 20°C for a period of 5 days is called Biochemical Oxygen Demand (BOD) and its value is expressed in ppm.

● BOD is used as- a measure of degree of water pollution. Clean water would have BOD value less than 5 ppm whereas highly polluted water has BOD value of 17 ppm or more.

Chemical oxygen demand (COD):

● BOD measurement takes 5 days so another parameter called the Chemical Oxygen Demand (COD) is measured.

● Chemical Oxygen Demand (COD) 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 K2Cr2O7 in acid medium for a period of 2 hrs.

ii) a. Viable particulates:

The viable particulates are the small size living organisms such as bacteria, fungi, moulds, algae, etc. which are dispersed in air. Some of the fungi cause allergy in human beings and diseases in plants.

b. Non-viable particulates:

The non-viable particulate are small solid particles and liquid droplets suspended in air. They help in the transportation of viable particles.

Eg: smoke, dust, mist, fog.


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

● Carbon monoxide is a poisonous gas produced as a result of incomplete combustion of coal are firewood. It is released into the air mainly by automobile exhaust.

● It binds with haemoglobin and form carboxy haemoglobin which impairs normal oxygen transport by blood and hence the oxygen carrying capacity of blood is reduced.

● This oxygen deficiency results in headache, dizziness, tension, loss of consciousness, blurring of eye sight and cardiac arrest.


36. What are the various methods you suggest to protect our environment from pollution?

1) Waste management: Environmental pollution can be controlled by proper disposal of wastes.

2) Recycling: A large amount of disposed waste material can be reused by recycling the waste, thus it reduces the land fill and converts waste into useful forms.

3) Substitution of less toxic solvents for highly toxic ones used in certain industrial processes.

4) Use of fuels with lower sulphur content (e.g., washed coal).

5) Growing more trees.

6) Control measures in vehicle emissions are adequate.

Efforts to control environmental pollution have resulted in development of science for synthesis of chemical favorable to environment and it is called green chemistry. 

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11th Chemistry : UNIT 15 : Environmental Chemistry : Brief questions and answers: Chemistry: Environmental Chemistry |

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