Question 1

Question 8Give balanced equations for the formation of sulphuric acid in acid rain, when a fossil fuel is burnt in an electric power station.

Accepted Answer

When a fossil fuel is burnt in an electric power station sulphur dioxide is formed:S + O2 ⟶ SO2Sulphur dioxide reacts with water vapour to form sulphurous acidH2O + SO2 ⟶ H2SO3 [aq.]Sulphur dioxide can also be oxidized to sulphur trioxide [SO3]2SO2 + O2 ⟶ 2SO3[The reaction is catalyzed by dust particles and water droplets].Sulphur trioxide reacts with water vapour in air forming sulphuric acidH2O + SO3 ⟶ H2SO4 [aq.]Thus, the acidity of rain is due to reaction of oxides of sulphur with water vapour forming dilute acids.

Question 2

Question 13State the impact of acid rain on the environment, other than soil chemistry and water bodies.

Accepted Answer

Acid rain affects :Plants in numerous ways — affects transpiration, decolourises leaf pigments, retards growth of crops and reduces rate of photosynthesis.Humans — Acid rain gets absorbed by plants, animals and directly or indirectly toxicity enters food chain affecting humans.Material Damage — Corrodes metallic surfaces, disintegrates paper and leather, weakens building material such as statues, sculptures, marbles, limestone [CaCO3] etc.CaCO3 + H2SO4 ⟶ CaSO4 + H2O + CO2

Question 3

Question 15State what are 'green house gases' and name the major green house gases.

Accepted Answer

Green house gases are those gases that contribute effectively in retaining heat in the atmosphere.Major green house gases are carbon dioxide, methane, water vapours, oxides of nitrogen and chlorofluorocarbons.

Question 4

Question 16State what is meant by the term – 'green house effect' and state it's consequence.

Accepted Answer

Green house effect is the warming up of the earth's surface, due to concentration or blanketing effect of the green house gases.The green house effect results in rise of atmospheric temperature which is not confined to one region but also has a global impact and is termed as global warming.

Question 5

Question 17Explain how global warming takes place in the presence of green house gases. Give a reason why the surface temperature of earth is maintained in absence of green house gases.

Accepted Answer

The green house effect results in rise of atmospheric temperature which is not confined to one region but also has a global impact and is termed as global warming.In absence of green house gases the surface temperature on earth is maintained since -The solar radiations emitted as heat radiations, passes through the clear atmosphere.It reaches the earth's surface where it is absorbed and retained.Some of the absorbed heat radiations is reflected back into the atmosphere. [radiations from the earth takes place in two ways - reflected solar radiation and emitted thermal infra red radiations]Thus, a balance is maintained between the heat energy absorbed by the earth and radiated from the earth.

Question 6

Question 18Give balanced equations for formation of carbon dioxide – a major green house gas, during combustion of fossil fuels.

Accepted Answer

Balanced equations for formation of carbon dioxide during combustion of fossil fuels are given below:Burning of CoalC + O2 ⟶ CO2 + ΔBurning of Natural gasCH4 + 2O2 ⟶ CO2 + 2H2O + Δ

Question 7

Question 19State two natural and two man-made sources of the green house gas – methane.

Accepted Answer

Two natural sources of Methane are:Bacterial decay of vegetable matter releases marsh gas which is mainly methane.Natural gas associated with petroleum contains about 75% of methane.Two man-made sources of Methane are:Natural wet lands and rice paddiesGas drilling, Coal mining, biomass burning

Question 8

Question 20'Oxides of nitrogen namely nitrous oxide, are released into the atmosphere from varied sources'. Explain the statement with relevant sources.

Accepted Answer

Oxides of nitrogen (namely nitrous oxide), are released into the atmosphere from various natural and man-made sources. The natural sources are:Anaerobic respiration — Activities of micro organisms in soil release nitrogen, nitric oxide and nitrous oxide.The lightning discharge in the atmosphere creates high temperatures causing Nitrogen (N2) and Oxygen (O2) to combine forming Oxides of Nitrogen.The man-made sources are:Use of nitrogenous fertilizers for agricultural activities release oxides of nitrogen.Automobile exhausts.Burning of biomass.

Question 9

Question 21State the impact of green house gases on geographic, climatic and agricultural conditions.AnswerImpact of green house gases on:Geographic conditions — Global warming increases melting of ice-caps which results in rising of sea levels causing coastal floating and erosion.Climatic conditions — Tropical regions experience more rainfall. Northern latitudes experience shorter and wetter winters.Agricultural conditions — Affects due to climatic changes:the life cycle of trees and survival and reproduction of plants.the soil fertility and amount of soil water retained in the soil.

Accepted Answer

Answer: Geographic conditions, Climatic conditions, Agricultural conditions

Question 10

Question 22Give the options for reducing green house gases by use of fuels better than fossil fuels.

Accepted Answer

The following fuels can be used which are better than fossil fuels as they release less green house gases:Liquefied Petroleum Gas [L.P.G.] - contains mostly propane [C3H8]Liquefied Natural Gas [L.N.G.] - contains mostly methane [CH4]Compressed Natural Gas [C.N.G.] - similar to L.P.G. but is not liquefied.

Question 11

Question 23State three renewable energy sources which cause less or no pollution.

Accepted Answer

Renewable sources of energy are:Solar energy [from sun's stored energy]Wind energy [from windmills]Hydropower energy [from high dams]

Question 12

Question 24Explain how promoting 'afforestation' and checking 'deforestation' reduces the release of green house gases.

Accepted Answer

Promoting afforestation means to induce more growth of plantation and forests. This helps to absorb green house gas - carbon dioxide during photosynthesis.6CO2+12H2O→ChlorophyllSunlightC6H12O6+6H2O+6O26	ext{CO}_2 + 12	ext{H}_2	ext{O} \xrightarrow[	ext{Chlorophyll}]{	ext{Sunlight}} 	ext{C}_6	ext{H}_{12}	ext{O}_6 + 	ext{6H}_	ext{2}	ext{O} + 6	ext{O}_26CO2​+12H2​OSunlightChlorophyll​C6​H12​O6​+6H2​O+6O2​Checking deforestation means to reduce burning of forests and biomass. This helps to control the emission of green house gases.

Question 13

Question 25What is an ozone layer. State the distribution of the ozone layer in the stratosphere.

Accepted Answer

Ozone layer is the layer in the earth's atmosphere which contains relatively high concentration of ozone. It absorbs 97-99% of the sun's high frequency U.V. light which is damaging to life on earth. Thus, Ozone layer protects life on earth from harmful solar rays.Distribution of the Ozone Layer in the Stratosphere:Ozone layer is mainly located approximately 20-30 kms above the earth's surface.The thickness of the ozone layer varies geographically and seasonally.It is less thicker near the equator and larger towards the poles.It is generally thicker during spring in the northern hemisphere.Most of the ozone is created over the tropics, but the stratoscopic wind circulation transports it polewards to northern and southern hemispheres.

Question 14

Question 26Give balanced equations for formation of ozone molecules from oxygen molecules. What type of reaction takes place, during the formation.

Accepted Answer

Highly energetic ultraviolet radiations from the sun breaks the oxygen molecule [O2] into two oxygen atoms. This reaction is photodissociation or photolysis.Highly reactive oxygen atom [O] can then react with oxygen molecule [O2] to form ozone [O3]O2 →lightU.V.\xrightarrow[	ext{light}]{	ext{U.V.}}U.V.light​ [O] + [O]O2 + [O] ⟶ O3 [ozone]

Question 15

Question 27How is the 'ozone oxygen cycle' maintained in the stratosphere and state what disturbs the balance, resulting in ozone depletion or destruction, Give balanced equation for the same.

Accepted Answer

Ozone is formed in the stratosphere — Highly energetic ultraviolet radiations from the sun breaks the oxygen molecule [O2] into two atoms. This reaction is photodissociation or photolysis.Highly reactive oxygen atom [O] can then react with oxygen molecule [O2] to form ozone [O3]O2 →lightU.V.\xrightarrow[	ext{light}]{	ext{U.V.}}U.V.light​ [O] + [O]O2 + [O] ⟶ O3 [ozone]Ozone is also broken down in the stratosphere — In unpolluted air containing minimal chemical compounds, unstable ozone molecule, in presence of solar radiations may split into molecular oxygen [O2] and an atom of atomic oxygen [O].The atomic oxygen then combines with another ozone molecule to form two molecules of molecular oxygen.O3 →lightU.V.\xrightarrow[	ext{light}]{	ext{U.V.}}U.V.light​ O2 + [O]O3 + [O] ⟶ 2O2Thus a continuing process called 'ozone oxygen cycle' is maintained between the amount of ozone [O3] being produced and being destroyed. As a result, the total concentration of ozone remains almost the same.The balance is disturbed by release of chemicals — such as chlorofluorocarbons containing atomic chlorine and bromine and other free radicals which breaks the ozone molecule causing ozone depletion.

Question 16

Question 28Enumerate the damage to humans, animals and plants caused due to ozone depletion.

Accepted Answer

Damage to Humans and Animals:Sun burn and skin cancerEye cataract and eye damageEarly aging of skinWeakening of immune systemDisruption in function of DNASevere damage to cells of animals.Damage to plants:Retards plant growth.Inhibits pollen germinationReduces chlorophyll contentAffects the quality of vegetablesDisrupts ecosystemIncreases harmful mutations

Question 17

Question 29Name the chemicals responsible for destruction of the ozone layer. State the main chemical from these chemicals, which is responsible for more than 80% ozone depletion. State the man-made applications which make use of that chemical.

Accepted Answer

Chemicals responsible for ozone depletion are :Chlorofluorocarbons [CFC i.e., CFCl3]Methyl chloride [CH3Cl]Methyl bromide [CH3Br]Carbontetrachloride [CCl4]BromofluorocarbonsMethane [CH4]Nitrous oxide [N2O]Out of the above chemicals, Chlorofluorocarbons (CFCs) is the main chemical responsible for more than 80% ozone depletion.Man-made applications making use of Chlorofluorocarbons (CFCs) are:Aerosol spraysCoolants in refrigeration and A.C.'sDrycleaning fluidsCleansing agents for cleaning electronic components

Question 18

Question 30State the role of chlorofluorocarbons in ozone destruction or depletion [no equations required].

Accepted Answer

Ozone is broken down by chlorofluorocarbons in the following way:Chlorofluorocarbons are broken down by ultraviolet radiations in the stratosphere.By products of the breakdown results in increase in levels of free radicals like atomic chlorine [Cl].The free radicals reacts with ozone to form ClO[g]. This causes ozone depletion. The Cl free radicals initiate and catalyze a chain reaction capable of breakdown of over 1,00,000 ozone molecules resulting in ozone depletion.

Question 19

Question 31Enumerate methods of protecting the ozone layer and preventing it's depletion.

Accepted Answer

Ozone layer can be protected by :Use of products that contain CFC's to be replaced by alternative products.Substitutes for CFC's have been initiated by scientists and use of HCFC [hydro chlorofluorocarbons] is being considered. Labelling products as CFC free is initiated.International Treaty [Montreal protocol] was also initiated to prevent ozone depletion.

Question 20

Question 9(a) State the main sources and effects of carbon monoxide.(b) Give the mechanism of the action of carbon monoxide.

Accepted Answer

(a) Carbon monoxide is formed by incomplete combustion of fuels in homes, factories and automobiles.Harmful effects of carbon monoxide :Carbon monoxide is a highly poisonous gas. If inhaled, it binds with haemoglobin 200 times more strongly than oxygen reducing the blood's ability to carry oxygen by converting haemoglobin into carboxyhaemoglobin. So, even in small quantities, it is fatal and can lead to death.(b) When inhaled, carbon monoxide enters the bloodstream through the lungs. It binds to haemoglobin, which carries oxygen to body tissues. Carbon monoxide binds with haemoglobin 200 times more strongly than oxygen, so even small amounts in the air can greatly affect the body. It reduces the blood's ability to carry oxygen by converting haemoglobin into carboxyhaemoglobin. The heart and brain, being highly sensitive to oxygen deprivation, are most severely impacted by carbon monoxide exposure. In high concentrations, carbon monoxide can lead to death by paralyzing normal brain function.

Atmospheric Pollution

Additional Questions

Exercise 8A

Exercise 8B

Exercise 8C

Exercise 8D Descriptive Type

Exercise 8D Multiple Choice Type

Exercise 8D Short Answer Type

Exercise 8D Structuredapplicationskill Type

Unit Test Paper 8 — Atmospheric Pollution