Atmospheric Pollution

Name -
(a) any two natural sources of atmospheric pollution.

(b) any two gases which are responsible for the formation of acid rain.

Answer

Two natural sources of atmospheric pollution are:

1. Disintegration of rocks and soil.
2. Decay of plants and animals, volcanic eruptions.

Two gases which are responsible for the formation of acid rain are:

1. Oxides of sulphur [SO₂]
2. Oxides of nitrogen [NO₂]

State two effects of ozone depletion.

Answer

1. Harmful ultraviolet rays will reach the earth and cause damage.
2. Humans, animals and plants will be adversely affected by the harmful effects of ultraviolet radiations.

State two ways by which global warming can be reduced.

Answer

Global warming can be reduced by reducing the emission of greenhouse gases by:

1. Using different fuels which release less greenhouse gases:
   1. Liquefied Petroleum Gas [L.P.G.] — contains mostly propane [C₃H₈]
   2. Liquefied Natural Gas [L.N.G.] — contains mostly methane [CH₄]
   3. Compressed Natural Gas [C.N.G.] — similar to L.P.G. but is not liquefied.
2. Using renewable energy resources like:
   1. Solar energy [from sun's stored energy]
   2. Wind energy [from windmills]
   3. Hydropower energy [from high dams]

State an advantage of CNG [compressed natural gas].

Answer

CNG is an alternative to petrol and diesel since it causes minimum pollution. It does not contain lead and lowers maintenance cost as compared to vehicles with other forms of fuels.

Explain the term 'global warming'.

Answer

The warming up of the earth's surface, due to concentration or blanketing effect of the greenhouse gases (Greenhouse effect) results in the rise of atmospheric temperatures. This is not confined to one region but has a global impact and is termed as global warming.

State -
(a) what is meant by the term 'acid rain'. Give any two impacts of acid rain.

(b) an advantage of using solar energy.

Answer

The term 'acid rain' refers to the various ways in which the acids formed in the atmosphere - condense and fall on the earth resulting in acid rain.

Impacts of acid rain :

1. Nutrient leaching — The hydrogen ions which are added to the soil when acid rain falls on the earth interact chemically with existing soil minerals.
   H₂SO₄ ⇌ 2H¹⁺ + SO₄^2-
   Minerals like potassium and calcium interact with the H¹⁺ ions and are displaced from the soil, thus the soil is deprived of nutrients.
2. Affects marine organisms — Toxic metals like mercury, lead, zinc present in the soil, get leached by acid rain thus toxicity enters rivers and streams and destroys aquatic plants and animals.

An advantage of using solar energy:

Solar energy is a renewable source of energy that does not cause pollution and helps in reducing global warming as it does not emit greenhouse gases.

Explain the methods of preventing acid rain.

Answer

Methods of preventing acid rain are:

1. Using alternate energy sources — alternatives to burning of fossil fuels such as compressed natural gas [C.N.G.] or use of cleaner energy sources such as hydro power or wind energy causes almost no pollution.
2. Usage of technical devices — such as catalytic converters, which can reduce nitrogen oxide emissions from automobiles [usage of electrostatic precipitators in industries].

State how CFCs break ozone in the stratosphere.

Answer

The breakdown of ozone by CFCs in the stratosphere is brought about in the following way:

1. Chlorofluorocarbons are broken down by ultraviolet radiations in the stratosphere.
2. By products of the breakdown of CFCs results in increase in levels of free radicals of atomic chlorine [Cl].
3. The free radicals initiate and catalyse a chain reaction by reacting with ozone to form chlorine monoxide (ClO) and oxygen (O₂). These reactions are capable of breakdown of over 1,00,000 ozone molecules resulting in ozone depletion.

Describe the methods of saving the ozone layer.

Answer

1. Use of products that contain CFCs to be replaced by alternative products.
2. Substitutes for CFCs have been initiated by scientists and use of HCFC [hydrochlorofluorocarbons] is being considered. Labelling products as CFC free is initiated.
3. International Treaty [Montreal protocol] was also initiated to prevent ozone depletion.

Name four gaseous atmospheric pollutants.

Answer

Four gaseous pollutants are:

1. Oxides of sulphur [SO₂],
2. Oxides of nitrogen [NO],
3. Oxides of carbon [CO₂],
4. Hydrogen sulphide [H₂S]

State the two forms of deposition of acid rain with suitable examples of each form of deposition.

Answer

The two forms of depositions of acid rain are:

1. Wet deposits - rain, snow, fog, dew
2. Dry deposits - particles [containing sulphates and nitrates]

State the natural and man-made sources of the two pollutants responsible for acid rain.

Answer

1. Natural sources — bacterial decomposition, forest fires, volcanic eruptions
2. Man-made sources — power, industrial and smelting plants and automobile exhausts.

Name the major green house gases.

Answer

Major green house gases are carbon dioxide, methane, water vapours, oxides of nitrogen and chlorofluorocarbons.

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

Answer

Two natural sources of Methane are:

1. Bacterial decay of vegetable matter releases marsh gas which is mainly methane.
2. Natural gas associated with petroleum contains about 75% of methane.

Two man-made sources of Methane are:

1. Natural wet lands and rice paddies
2. Gas drilling, Coal mining, biomass burning

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

Answer

Renewable sources of energy are:

1. Solar energy [from sun's stored energy]
2. Wind energy [from windmills]
3. Hydropower energy [from high dams]

Name the chemicals responsible for destruction of the ozone layer.

Answer

Chemicals responsible for ozone depletion are :

1. Chlorofluorocarbons [CFC i.e., CFCl₃]
2. Methyl chloride [CH₃Cl]
3. Methyl bromide [CH₃Br]
4. Carbontetrachloride [CCl₄]
5. Bromofluorocarbons
6. Methane [CH₄]
7. Nitrous oxide [N₂O]

State what is meant by the term 'atmospheric pollution'.

Answer

Atmospheric pollution means conditions of air made unclean due to introduction of foreign elements from (i) Natural sources (ii) Man made sources to the air so as to cause adverse effects on living organisms on earth.

Explain the term 'acid rain'.

Answer

The term 'acid rain' refers to the various ways in which the acids formed in the atmosphere condense and fall on the earth.

Burning of fossil fuels is an important source of the pollutant – 'oxides of sulphur' responsible for acid rain. State what are 'fossil fuels'. Name the principal fossil fuels. State why sulphur dioxide is emitted on burning a fossil fuel. Give a balanced equation for the same.

Answer

Fuels that are derived from organic remains of plants and animals are called fossil fuels.
Principal fossil fuels — coal, petroleum [oil], natural gas.
Sulphur impurities are present in fossil fuels which produce sulphur dioxide when the fossil fuel is burnt. Balanced chemical equation for the same is given below:
S + O₂ ⟶ SO₂

Give balanced equations for the formation of H₂SO₄ in acid rain, when a fossil fuel is burnt in an electric power station.

Answer

1. When a fossil fuel is burnt in an electric power station sulphur dioxide is formed:
   S + O₂ ⟶ SO₂
2. Sulphur dioxide reacts with water vapour to form sulphurous acid
   H₂O + SO₂ ⟶ H₂SO₃ [aq.]
3. Sulphur dioxide can also be oxidized to sulphur trioxide [SO₃]
   2SO₂ + O₂ ⟶ 2SO₃
   [The reaction is catalyzed by dust particles and water droplets].
4. Sulphur trioxide reacts with water vapour in air forming sulphuric acid
   H₂O + SO₃ ⟶ H₂SO₄ [aq.]

Thus, the acidity of rain is due to reaction of oxides of sulphur with water vapour forming dilute acids.

Starting from nitrogen in air, enlist the reactions with the help of balanced equations, which result in the conversion of nitrogen in an internal combustion engine, to the acids formed which are responsible for acid rain.

Answer

1. Nitrogen combines with oxygen at high temperatures to give nitric oxide
   N₂ + O₂ ⟶ 2NO
2. Nitric oxide [NO] is oxidized to nitrogen dioxide [NO₂]
   2NO + O₂ ⟶ 2NO₂
3. Nitrogen dioxide [NO₂] reacts with water vapour to form nitrous acid [HNO₂] and nitric acid [HNO₃]
   H₂O + 2NO₂ ⟶ HNO₂ + HNO₃
   [The nitrogen dioxide may also dissolve in atmospheric moisture in the presence of oxygen of the air forming nitric acid in the free state].
   [2H₂O + 4NO₂ + O₂ ⟶ 4HNO₃]

Thus the acidity in the rain is due to reaction of oxides of nitrogen with water vapour forming dilute acids.

Explain the basic function of a catalytic converter in an internal combustion engine.

Answer

The basic function of a catalytic converter in an internal combustion engine is to help reduce pollution.

The reduction catalyst [Pt/Pd] in a converter separates the nitrogen atom from NO and NO₂ molecules freeing oxygen in the form of O₂ molecule.

2NO ⟶ N₂ + O₂
2NO₂ ⟶ N₂ + 2O₂

Thus, the oxides of nitrogen which are pollutants are converted to free nitrogen.

State why acid rain causes 'nutrient leaching' when it falls on the earth.

Answer

The hydrogen ions which are added to the soil - when acid rain falls on the earth - interact chemically with existing soil minerals.

H₂SO₄ ⇌ 2H¹⁺ + SO₄^2-

Minerals like potassium and calcium interact with the H¹⁺ ions and are displaced from the soil, thus the soil is deprived of nutrients causing nutrient leaching.

Give reasons why acid rain affects marine organisms.

Answer

Toxic metals like - mercury, lead, zinc present in the soil, get leached by acid rain thus toxicity enters rivers and streams and destroys aquatic plants and animals.

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

Answer

Acid rain affects:

1. Plants in numerous ways — affects transpiration, decolourises leaf pigments, retards growth of crops and reduces rate of photosynthesis.
2. Humans — Acid rain gets absorbed by plants, animals and directly or indirectly toxicity enters food chain affecting humans.
3. 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

Enumerate the ways by which acid rain can be controlled to prevent it's adverse effects on the environment.

Answer

Ways to control acid rain:

1. Using alternate energy sources - alternatives to burning of fossil fuels such as compressed natural gas [C.N.G.] or use of cleaner energy sources such as hydro power or wind energy causes almost no pollution.
2. Usage of technical devices - such as catalytic converters, which can reduce nitrogen oxide emissions from automobiles [usage of electrostatic precipitators in industries].

State what are 'green house gases'.

Answer

Green house gases are those gases that contribute effectively in retaining heat in the atmosphere.

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

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.

Explain 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.

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 -

1. The solar radiations emitted as heat radiations, passes through the clear atmosphere.
2. It reaches the earth's surface where it is absorbed and retained.
3. Some of the absorbed heat radiation is reflected back into the atmosphere. [radiation from the earth takes place in two ways - reflected solar radiation and emitted thermal infrared radiations]

Thus, a balance is maintained between the heat energy absorbed by the earth and radiated from the earth.

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

Answer

Balanced equations for formation of carbon dioxide during combustion of fossil fuels are given below:

1. Burning of Coal
   C + O₂ ⟶ CO₂ + Δ
2. Burning of Natural gas
   CH₄ + 2O₂ ⟶ CO₂ + 2H₂O + Δ

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

Answer

Oxides of nitrogen (namely nitrous oxide), are released into the atmosphere from various natural and man-made sources. The natural sources are:

1. Anaerobic respiration — Activities of micro organisms in soil release nitrogen, nitric oxide and nitrous oxide.
2. 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:

1. Use of nitrogenous fertilizers for agricultural activities release oxides of nitrogen.
2. Automobile exhausts.
3. Burning of biomass.

State the impact of green house gases on geographic, climatic and agricultural conditions.

Answer

Impact of green house gases on:

1. Geographic conditions — Global warming increases melting of ice-caps which results in rising of sea levels causing coastal flooding and erosion.
2. Climatic conditions — Tropical regions experience more rainfall. Northern latitudes experience shorter and wetter winters.
3. Agricultural conditions — Affects due to climatic changes:
   1. the life cycle of trees and survival and reproduction of plants.
   2. the soil fertility and amount of soil water retained in the soil.

State the options for reducing green house gases by use of fuels better than fossil fuels.

Answer

The following fuels can be used which are better than fossil fuels as they release less green house gases:

1. Liquefied Petroleum Gas [L.P.G.] - contains mostly propane [C₃H₈]
2. Liquefied Natural Gas [L.N.G.] - contains mostly methane [CH₄]
3. Compressed Natural Gas [C.N.G.] - similar to L.P.G. but is not liquefied.

State what is an ozone layer. State the distribution of the ozone layer in the stratosphere.

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:

1. Ozone layer is mainly located approximately 20-30 kms above the earth's surface.
2. The thickness of the ozone layer varies geographically and seasonally.
3. It is thinner near the equator and larger towards the poles.
4. It is generally thicker during spring in the northern hemisphere.
5. Most of the ozone is created over the tropics, but the stratospheric wind circulation transports it polewards to northern and southern hemispheres.

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

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 $\xrightarrow[\text{light}]{\text{U.V.}}$ [O] + [O]

O₂ + [O] ⟶ O₃ [ozone]

How 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.

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 $\xrightarrow[\text{light}]{\text{U.V.}}$ [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 $\xrightarrow[\text{light}]{\text{U.V.}}$ O₂ + [O]

O₃ + [O] ⟶ 2O₂

Thus 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.

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

Answer

Damage to Humans and Animals:

1. Sunburn and skin cancer
2. Eye cataract and eye damage
3. Early aging of skin
4. Weakening of immune system
5. Disruption in function of DNA
6. Severe damage to cells of animals.

Damage to plants:

1. Retards plant growth.
2. Inhibits pollen germination
3. Reduces chlorophyll content
4. Affects the quality of vegetables
5. Disrupts ecosystem
6. Increases harmful mutations

State the main chemical - which is responsible for more than 80% ozone depletion. State the man-made applications which make use of that chemical.

Answer

Chlorofluorocarbons (CFCs) is the main chemical responsible for more than 80% ozone depletion.

Man-made applications making use of Chlorofluorocarbons (CFCs) are:

1. Aerosol sprays
2. Coolants in refrigeration and A.C.s
3. Drycleaning fluids
4. Cleansing agents for cleaning electronic components

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

Answer

Ozone is broken down by chlorofluorocarbons in the following way:

1. Chlorofluorocarbons are broken down by ultraviolet radiations in the stratosphere.
2. By products of the breakdown results in increase in levels of free radicals like atomic chlorine [Cl].
3. 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.

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

Answer

Ozone layer can be protected by:

1. Use of products that contain CFCs to be replaced by alternative products.
2. Substitutes for CFCs have been initiated by scientists and use of HCFC [hydrochlorofluorocarbons] is being considered. Labelling products as CFC free is initiated.
3. International Treaty [Montreal protocol] was also initiated to prevent ozone depletion.

Enumerate the main substances present in water, which are

(a) beneficial to life (b) harmful to life

State the adverse effects of 'Minamata' disease.

Answer

(a) The main substances present in water which are beneficial to life are:

1. Dissolved oxygen in water which is essential for aquatic life.
2. Essential minerals like calcium, potassium, zinc and copper.

(b) The main substances present in water which are harmful to life are:

1. Toxic heavy metals like mercury and lead.
2. Agricultural wastes like pesticides.
3. Industrial chemical wastes like benzene.
4. Bacteria and viruses like E. coli.

Minamata disease is a severe neurological disorder caused by mercury poisoning.
The adverse effects of Minamata disease are:

1. Severe sensory disturbances.
2. Lack of coordination.
3. Hearing and speech impairment.

A source which releases a foul smelling gas which is oxidised to a pollutant, which causes acid rain.

1. Smelting plants
2. Internal combustion engines
3. Organic matter on bacterial decomposition
4. Sulphuric acid plants

Answer

Organic matter on bacterial decomposition

Reason — When organic matter decomposes by bacterial action, it releases hydrogen sulphide, a foul-smelling gas. This gas gets oxidised in air to form sulphur dioxide which further reacts with water vapour to produce sulphuric acid, causing acid rain.
Smelting plants release sulphur dioxide directly, but not a foul-smelling gas. Internal combustion engines release nitrogen oxides. Sulphuric acid plants release sulphur dioxide, not typically a foul-smelling gas.

The pH of acid rain on pH scale is -

1. Less than pH of natural rain water
2. More than pH of natural rain water
3. Same as pH of natural rain water
4. More than pH of pure water

Answer

Less than pH of natural rain water

Reason — Natural rainwater has a pH of about 5 to 6 due to presence of carbon dioxide which dissolves in rain water to form weak carbonic acid. Acid rain contains strong acids such as sulphuric acid and nitric acid, so its pH ranges between 5.6 to 3.5.

The main natural source of carbon dioxide contributing to global warming -

1. Power plants
2. Bacterial decay of vegetable matter
3. Exhaust from automobiles
4. Burning of fossil fuels

Answer

Bacterial decay of vegetable matter

Reason — During bacterial decomposition of dead plants and organic matter, carbon compounds break down and release carbon dioxide naturally into the atmosphere.
Power plants, exhaust from automobiles, Burning of fossil fuels are man-made sources.

The atmospheric pollutant which contributes to both ozone depletion & global warming.

1. Carbon tetrachloride
2. Methane
3. Carbon dioxide
4. Bromofluorocarbon

Answer

Bromofluorocarbon

Reason — Bromofluorocarbons contain bromine and fluorine. In the stratosphere, bromine-containing free radicals destroy ozone molecules, causing ozone depletion. Bromofluorocarbons also act as greenhouse gases and trap heat in the atmosphere, thus contributing to global warming.
Carbon tetrachloride mainly causes ozone depletion. Methane and carbon dioxide mainly cause global warming.

Photodissociation reaction involves the conversion -

1. O₂ ⟶ O₃
2. O₃ ⟶ O₂ + [O]
3. O₃ ⟶ 2O₂
4. O₂ ⟶ 2[O]

Answer

O₂ ⟶ 2[O]

Reason — O₂ $\xrightarrow[\text{light}]{\text{U.V.}}$ [O] + [O]

Highly energetic ultraviolet radiations from the sun breaks down the oxygen molecule into two oxygen atoms. This chemical reaction is called photodissociation or photolysis.

Assertion: Green house effect results in rise in atmospheric temperature & has a global impact.

Reason: Promoting afforestation helps in absorbing green house gas i.e. CO₂ during photosynthesis.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true and R is false.
4. A is false and R is true.

Answer

Both A and R are true but R is not the correct explanation of A.

Reason — A is true as the greenhouse effect traps heat in the atmosphere, leading to global warming and climate change worldwide.
R is true as plants absorb carbon dioxide during photosynthesis, helping reduce greenhouse gases.

Therefore, Both A and R are true but R is not the correct explanation of A is the correct option.

State why natural rain water produced in an unpolluted atmosphere is slightly acidic. Give a balanced equation of the same.

Answer

Natural rain water produced in an unpolluted atmosphere is slightly acidic as CO₂ present in traces in unpolluted air dissolves in rain water forming weak carbonic acid [H₂CO₃].

H₂O + CO₂ ⟶ H₂CO₃ [carbonic acid]

During metallurgy – smelting plants produce sulphur dioxide, when metallic sulphides are roasted in air. Give a balanced equation, when the same gas is released from organic matter.

Answer

Organic matter releases hydrogen sulphide [H₂S] on bacterial decomposition. Hydrogen sulphide is oxidised in air to sulphur dioxide.

2H₂S + 3O₂ ⟶ 2H₂O + 2SO₂

State why high temperatures in internal combustion engines release pollutant – oxides of nitrogen.

Answer

In internal combustion engines, combustion of fossil fuel occurs with an oxidiser (air). The air drawn from the atmosphere contains about 80% nitrogen. The nitrogen combines with oxygen at high temperature producing oxides of nitrogen.

N₂ + O₂ ⟶ 2NO [at high temp.]

Thus, exhaust gases of all internal combustion engines release oxides of nitrogen.

State the impact of global warming on the countries economy.

Answer

The impact of global warming on the countries economy are:

1. Higher temperatures, droughts and floods reduce crop production, causing losses to farmers and increase in food prices.
2. Cyclones, floods, heat waves and storms damage roads, buildings, industries and public property, leading to huge economic losses.
3. Reduction in forest resources, fisheries and wildlife affects industries dependent on them and decreases tourism income.

Differentiate between global warming & climate change.

Answer

Differences between global warming and climate change are:

State why global warming & ozone depletion are directly or indirectly interconnected.

Answer

Global warming and ozone depletion are directly or indirectly interconnected because:

1. In the stratosphere, CFCs break down ozone molecules and cause ozone depletion. At the same time, CFCs trap heat in the atmosphere and act as greenhouse gases, contributing to global warming.
2. The ozone layer absorbs harmful ultraviolet (UV) radiation from the Sun. When ozone is depleted, more UV rays enter the atmosphere. This changes atmospheric heating patterns and can disturb climate systems, wind circulation and rainfall patterns.

Give a reason why ozone holes occur in the Antarctic & more so during spring.

Answer

Ozone holes occur mainly over the Antarctic region because very low temperatures in the Antarctic stratosphere help in the formation of polar stratospheric clouds. On the surface of these clouds, inactive chlorine compounds formed from CFCs are converted into active chlorine radicals.
During spring, sunlight returns and activates these chlorine radicals. They rapidly break down ozone molecules, so ozone depletion becomes maximum during spring.

How can the causes of acid rain & ozone depletion be compared.

Answer

The causes of acid rain and ozone depletion can be compared as follows:

1. Acid rain is caused mainly by sulphur dioxide and nitrogen oxides whereas ozone depletion is caused mainly by chlorofluorocarbons.
2. Acid rain mainly affects the lower atmosphere and Earth’s surface whereas ozone depletion affects the stratospheric ozone layer.

State how the effects of acid rain and greenhouse gases are related.

Answer

The effects of acid rain and greenhouse gases are related in the following ways:

1. Both disturb ecological balance — Acid rain damages forests, crops, lakes and soil. Global warming changes climate, rainfall and temperature, affecting plants and animals.
2. Both affect water bodies and living organisms — Acid rain increases acidity of rivers and lakes, harming aquatic life. Global warming raises water temperature and causes melting of ice and sea-level rise.
3. Acid rain and greenhouse gases are both caused by atmospheric pollution and both adversely affect plants, animals, water bodies, soil and the overall ecological balance.

Compare the advantage of the green house effect over its disadvantage.

Answer

The advantages and disadvantages of the greenhouse effect are:

State how water vapour contributes to the green house effect.

Answer

Water vapour contributes to the greenhouse effect by absorbing and trapping heat radiated from the Earth’s surface. This trapped heat warms the atmosphere and prevents it from escaping into space easily. As global temperature rises, more water evaporates, increasing the amount of water vapour in the atmosphere, which further increases warming. Thus, water vapour acts as a greenhouse gas and strengthens the greenhouse effect.

State why acid rain is a regional problem, while global warming a global problem.

Answer

Acid rain is a regional problem because the pollutants causing it, mainly oxides of sulphur and nitrogen, form acids in the atmosphere and fall with rain, snow, fog or dew over a limited region. Hence, its effects are mainly seen on the soil, water bodies, plants, buildings and organisms of that region.

Global warming is a global problem because greenhouse gases like carbon dioxide, methane, water vapour and oxides of nitrogen spread throughout the atmosphere and retain heat due to their blanketing effect. This raises atmospheric temperature worldwide and causes global effects such as melting of ice-caps, rise in sea level and climatic changes.

Select the correct answer from the choice A, B, C given in each case.

1. The major pollutant released during burning of fossil fuels.
   A: Carbon monoxide B: Sulphur dioxide C: Hydrogen sulphide

2. The green house gas which on combustion produces another green house gas.
   A: Nitrous oxide B: Ozone C: Methane

3. The gas which in presence of U.V. light gives two atoms of the same gas.
   A: Oxygen B: Ozone C: Carbon dioxide

4. A chemical responsible for ozone depletion.
   A: Methyl acetylene B: Methyl chloride C: Methanol

5. A renewable source of energy which causes minimum or no pollution.
   A: Fossil fuel B: L.P.G. C: Hydro power.

Answer

1. B: Sulphur dioxide

2. C: Methane

3. A: Oxygen

4. B: Methyl chloride

5. C: Hydro power

Give balanced equations for the following conversions [one or two steps].

1. Sulphur trioxide to sulphuric acid – a constituent of acid rain.
2. Nitrogen to nitrogen dioxide – in an internal combustion engine.
3. Methane to carbon dioxide – a green house gas.
4. A molecule of ozone to two molecules of oxygen gas.
5. Oxygen to ozone gas by photolysis.

Answer

1. Sulphur trioxide to sulphuric acid
   H₂O + SO₃ ⟶ H₂SO₄

2. Nitrogen to nitrogen dioxide in internal combustion engine
   N₂ + O₂ ⟶ 2NO [At High Temperatures]
   2NO + O₂ ⟶ 2NO₂

3. Methane to carbon dioxide
   CH₄ + 2O₂ ⟶ CO₂ + 2H₂O + Δ

4. A molecule of ozone to two molecules of oxygen gas
   O₃ $\xrightarrow[\text{light}]{\text{U.V.}}$ O₂ + [O]
   O₃ + [O] ⟶ 2O₂

5. Oxygen to ozone gas by photolysis
   O₂ $\xrightarrow[\text{light}]{\text{U.V.}}$ [O] + [O]
   O₂ + [O] ⟶ O₃ [ozone]

Give reasons for the following.

Natural rain water does not have a pH of 7 [i.e. neutral]

Answer

Natural rain water produced in unpolluted air is slightly acidic as CO₂ present in traces in unpolluted air dissolves in rain water forming weak carbonic acid [H₂CO₃].

H₂O + CO₂ ⟶ H₂CO₃ [carbonic acid]

Give reasons for the following.

A catalytic converter in an internal combustion engine reduces pollution.

Answer

The reduction catalyst [Pt/Pd] of the catalytic converter separates the nitrogen atom from NO and NO₂ molecules freeing oxygen in the form of O₂ molecule.
2NO ⟶ N₂ + O₂
2NO₂ ⟶ N₂ + 2O₂

Thus, the oxides of nitrogen which are pollutants are converted to free nitrogen by the catalytic converter thereby reducing pollution.

Give reasons for the following.

In absence of green house gases the surface temperature of the earth is maintained.

Answer

In absence of green house gases the surface temperature on earth is maintained since -

1. The solar radiation emitted as heat radiation, passes through the clear atmosphere.
2. It reaches the earth's surface where it is absorbed and retained.
3. Some of the absorbed heat radiation is reflected back into the atmosphere. [radiation from the earth takes place in two ways - reflected solar radiation and emitted thermal infrared radiation]

Thus, a balance is maintained between the heat energy absorbed by the earth and radiated from the earth and the surface temperature of earth is maintained.

Give reasons for the following.

The formation of ozone involves a chemical reaction called photolysis.

Answer

Highly energetic ultraviolet radiations from the sun breaks the oxygen molecule [O₂] into two oxygen atoms. This chemical reaction is called photodissociation or photolysis.

The highly reactive oxygen atom [O] can then react with oxygen molecule [O₂] to form ozone [O₃]

O₂ $\xrightarrow[\text{light}]{\text{U.V.}}$ [O] + [O]

O₂ + [O] ⟶ O₃ [ozone]

Give reasons for the following.

Destruction of ozone layer is harmful for both humans and plants.

Answer

Destruction of ozone layer is harmful for humans because U.V. radiations from the sun cause the following damage to humans:

1. Sunburn and skin cancer
2. Eye cataract and eye damage
3. Early aging of skin
4. Weakening of immune system
5. Disruption in function of DNA
6. Severe damage to cells of animals.

U.V. radiations also damage plants in the following ways:

1. Retards plant growth.
2. Inhibits pollen germination
3. Reduces chlorophyll content
4. Affects the quality of vegetables
5. Disrupts ecosystem
6. Increases harmful mutations

Name or state the following:

1. An atmospheric pollutant produced during lightening discharge.
2. A form of wet deposition of acid rain other than rain water.
3. An atmospheric pollutant responsible for both global warming and ozone depletion.
4. A green house gas which contains carbon and hydrogen only.
5. The atom which reacts with oxygen to form ozone.

Answer

1. NO
2. Snow
3. Chlorofluorocarbons [CFCs]
4. CH₄ [methane]
5. Oxygen atom.

Acid rain has adverse effects on the environment. State the effect acid rain has on the following - i.e., A: Increases or B: Decreases

1. The nutrients present in the soil.
2. The acidity of the soil.
3. The fertility of the soil.
4. The pH of water bodies.
5. The rate of photosynthesis in plants.

Answer

1. Decreases
2. Increases
3. Decreases
4. Decreases
5. Decreases

The diagram represents the green house effect.

1. State why the effect is called 'global warming'.
2. Name a process which (a) releases (b) absorbs – green house gas – CO₂.
3. State an advantage of use of C.N.G. over combustion of fossil fuels.
4. Which of the following – biofertilizers or nitrogenous fertilizers reduces the green house gas – N₂O. Explain.
5. Does the sea level rise or fall due to global warming. Explain.

Answer

1. 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'.
2. Process which releases – CO₂ is respiration and
   the process which absorbs – CO₂ is photosynthesis.
3. C.N.G. causes minimum pollution. It does not contain lead and lowers maintenance cost as compared to vehicles with other forms of fuels.
4. Biofertilizers reduce the green house gas N₂O as nitrogenous fertilizers release N₂O when used in agricultural activities.
5. The sea level rises due to global warming as increase in temperature melts ice on mountains, ice-caps.