Atmospheric & Environmental Chemistry - Questions & Answers

1. PREVIOUS QUESTIONS

Short Answer Questions

1. Name - (a) any two natural sources of atmospheric pollution.
Answer: (a) Decay of plants & animals and volcanic eruptions.

(b) any two gases which are responsible for the formation of acid rain.
Answer: (b) Oxides of sulphur (SO₂) and Oxides of nitrogen (NO₂).

2. State - two effects of ozone depletion.
Answer: Ozone depletion causes skin cancer & eye cataract in humans, and retards plant growth & inhibits pollen germination in plants.

3. State - two ways by which global warming can be reduced.
Answer: Global warming can be reduced by using different eco-friendly fuels like L.P.G. and C.N.G., and by using renewable energy sources like solar energy and wind energy.

4. State - an advantage of CNG [compressed natural gas].
Answer: C.N.G. causes minimum pollution, does not contain lead, and lowers maintenance cost as compared to vehicles with other forms of fuels.

Long Answer Questions

1. Explain - the term 'global warming'.
Answer: The greenhouse effect results in a rise in atmospheric temperatures, which is not confined to one region but has a global impact. This rise in global temperature is termed global warming.

2. State - (a) what is meant by the term 'acid rain'. Give any two impacts of acid rain.
Answer: (a) Acid rain refers to rain (or any precipitation i.e. snow or fog) which has a pH less than 5.6. It is caused by atmospheric pollutants like sulphur dioxide and nitrogen oxides. Two impacts: It increases the acidity of the soil causing a reduction in fertility, and it corrodes metallic surfaces & weakens building materials such as marble and limestone.

(b) an advantage of using solar energy.
Answer: (b) Solar energy is a renewable energy source which causes almost no pollution.

3. Explain - the methods of preventing acid rain.
Answer: Acid rain can be controlled by using alternative energy sources (like C.N.G., hydro power, or wind energy) instead of burning fossil fuels, and by the usage of technical devices such as catalytic convertors in automobiles to reduce nitrogen oxide emissions.

4. State - how CFCs break ozone in the stratosphere.
Answer: Chlorofluorocarbons (CFCs) are broken down by U.V. radiations in the stratosphere, which releases active free radicals like atomic chlorine [Cl]. This atomic chlorine reacts with ozone [O₃] to form chlorine monoxide [ClO] and oxygen [O₂], initiating a chain reaction capable of breaking down over 100,000 ozone molecules.

5. Describe - the methods of saving the ozone layer.
Answer: The ozone layer can be protected by replacing products that contain CFCs with alternative products like HCFCs [hydrochlorofluorocarbons]. Labelling products as "CFC free" and strictly following International Treaties like the Montreal Protocol also helps prevent ozone depletion.

2. ADDITIONAL QUESTIONS

Short Answer Questions

1. Name - four gaseous atmospheric pollutants.
Answer: 1. Oxides of sulphur (SO₂, SO₃) 2. Oxides of nitrogen (NO, NO₂) 3. Oxides of carbon (CO, CO₂) 4. Hydrogen sulphide (H₂S).

2. State the two forms - of deposition of acid rain with suitable examples of each form of deposition.
Answer: 1. Wet deposits - rain, snow, fog, dew. 2. Dry deposits - particles containing sulphates & nitrates.

3. State the natural & man-made sources - of the two pollutants responsible for acid rain.
Answer: Oxides of sulphur: Natural source is bacterial decomposition and volcanic eruptions; Man-made source is burning of fossil fuels. Oxides of nitrogen: Natural source is lightening discharge; Man-made source is automobile exhausts and internal combustion engines.

4. Name - the major green house gases.
Answer: Carbon dioxide, methane, water vapour, oxides of nitrogen, and chlorofluorocarbons.

5. State two natural & two man-made sources - of the green house gas - methane.
Answer: Natural sources: Bacterial decay of vegetable matter (marsh gas) and natural gas. Man-made sources: Agricultural activities (rice paddies) and coal mining / gas drilling.

6. State three renewable energy sources - which cause less or no pollution.
Answer: Solar energy, Wind energy, and Hydro power.

7. Name the chemicals responsible - for destruction of the ozone layer.
Answer: Chlorofluorocarbons [CFCs], Methyl chloride, Methyl bromide, Carbon tetrachloride, Bromofluorocarbons, Methane, and Nitrous oxide.

Long Answer Questions

1. State what is meant by - the term 'atmospheric pollution'.
Answer: Atmospheric pollution refers to the conditions of air made unclean, due to the introduction of foreign elements from natural sources or man-made sources to the air so as to cause adverse effects on living organisms on earth.

2. Explain the term - 'acid rain'.
Answer: Acid rain refers to rain (or any precipitation like snow or fog) which has a pH of less than 5.6. It is a complex mixture of sulphuric acid, nitric acid, sulphurous acid, and nitrous acid, formed when oxides of sulphur and nitrogen interact with atmospheric water vapour.

3. 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: Fossil fuels are derived from the organic remains of plants & animals. The principal fossil fuels are coal, petroleum [oil], and natural gas. Sulphur dioxide is emitted on burning a fossil fuel because of the presence of sulphur impurities in coal. Equation: S + O₂ → SO₂.

4. Give balanced equations - for the formation of H₂SO₄ in acid rain, when a fossil fuel is burnt in an electric power station.
Answer: 1. S + O₂ → SO₂
2. 2SO₂ + O₂ → 2SO₃
3. H₂O + SO₃ → H₂SO₄ [aq.]

5. 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 is oxidised to nitrogen dioxide: 2NO + O₂ → 2NO₂
3. Nitrogen dioxide reacts with water vapour to form nitrous and nitric acid: H₂O + 2NO₂ → HNO₂ + HNO₃.

6. Explain the basic function - of a catalytic converter in an internal combustion engine.
Answer: The catalytic converter helps reduce pollution. The reduction catalyst [Pt/Pd] in the converter separates the nitrogen atom from NO and NO₂ molecules, freeing oxygen in the form of O₂ molecules, thus converting pollutant oxides of nitrogen to free nitrogen. Equations: 2NO → N₂ + O₂ and 2NO₂ → N₂ + 2O₂.

7. State why - acid rain causes 'nutrient leaching' when it falls on the earth.
Answer: Acid rain causes nutrient leaching because the hydrogen ions (H¹⁺) added to the soil from the acids interact chemically with existing soil minerals. Essential minerals like potassium & calcium interact with the H¹⁺ ions and get displaced from the soil, depriving the soil of nutrients.

8. Give reasons why - acid rain affects marine organisms.
Answer: Acid rain affects marine organisms because it leaches toxic metals like mercury, lead & zinc from the soil into rivers & streams, destroying aquatic plants & animals. Additionally, it lowers the pH of the water environment; most aquatic animals cannot survive when the pH drops below 4.

9. State the impact - of acid rain on the environment, other than soil chemistry & water bodies.
Answer: Other than soil and water, acid rain affects plants by altering transpiration, decolorising leaf pigments, and retarding crop growth. It affects humans indirectly as toxicity enters the food chain. It also causes material damage by corroding metallic surfaces and disintegrating building materials like marble and limestone.

10. Enumerate the ways - by which acid rain can be controlled to prevent its adverse effects on the environment.
Answer: Acid rain can be controlled by: 1) Using alternative, cleaner energy sources like C.N.G., hydro power, or wind energy instead of burning fossil fuels. 2) Using technical devices such as catalytic converters in automobiles to reduce nitrogen oxide emissions.

11. State what are - 'green house gases'.
Answer: Green house gases are those gases that contribute effectively in retaining heat in the atmosphere. Major ones include carbon dioxide, methane, water vapour, oxides of nitrogen, and chlorofluorocarbons.

12. State what is meant by the term - 'green house effect' and state its consequence.
Answer: Green house effect is the warming up of the earth's surface, due to the concentration or blanketing effect of the green house gases. Its main consequence is 'global warming'—a rise in atmospheric temperatures causing a global impact like melting of ice caps and climate changes.

13. 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: In the presence of greenhouse gases, the solar rays (long wave radiations or U.V. rays) pass through the atmosphere, but the heat radiation reflected back from the earth is trapped and retained due to the blanketing effect of these gases, causing global warming. In the absence of greenhouse gases, the surface temperature is maintained because there is a perfect balance between the heat energy absorbed by the earth from solar radiation and the thermal infra red radiation emitted back into the atmosphere.

14. Give balanced equations - for formation of carbon dioxide - a major green house gas, during combustion of fossil fuels.
Answer:
1. Burning of Coal: C + O₂ → CO₂ + Δ
2. Burning of Natural Gas (Methane): CH₄ + 2O₂ → CO₂ + 2H₂O + Δ

15. 'Oxides of nitrogen namely nitrous oxide, are released into the atmosphere from varied sources'. Explain the statement with relevant sources.
Answer: Nitrous oxide is released from both natural and man-made sources. Naturally, it is released during anaerobic respiration by the activities of microorganisms in the soil. Man-made sources include agricultural activities, specifically the use of nitrogenous fertilizers and soil cultivation.

16. State the impact - of green house gases on geographic, climatic and agricultural conditions.
Answer: 1. Geographic: Global warming increases melting of ice-caps resulting in rise in sea levels, coastal flooding & erosion. 2. Climatic: Tropical regions experience more rainfall, while Northern latitudes experience shorter & wetter winters. 3. Agriculture: It affects the life cycle of trees, survival & reproduction of plants, and the soil fertility.

17. State the options - for reducing green house gases by use of fuels better than fossil fuels.
Answer: Options for better fuels include Liquefied Petroleum Gas [L.P.G.], Liquefied Natural Gas [L.N.G.], and Compressed Natural Gas [C.N.G.], as they cause minimum pollution compared to traditional fossil fuels. Other options are using biofuels or biogas.

18. State - what is an ozone layer. State the distribution of the ozone layer in the stratosphere.
Answer: The ozone layer is a layer in the earth's atmosphere which contains a relatively high concentration of ozone. It is located in the stratosphere, approximately 20-30 kms above the earth. Its thickness varies geographically & seasonally; it is less thicker near the equator and larger towards the poles.

19. Give balanced equations - for formation of ozone molecules from oxygen molecules. What type of reaction takes place, during the formation.
Answer:
O₂ → (U.V. light) → [O] + [O]
O₂ + [O] → O₃ [ozone]
The reaction taking place is called a photodissociation or photolysis reaction.

20. 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: The cycle is maintained by a continuing process between the amount of ozone being produced and being destroyed, keeping the total concentration almost the same. This balance is disturbed by the release of chemicals like chlorofluorocarbons containing atomic chlorine or bromine, which act as free radicals and break the ozone molecule. Equation: Cl + O₃ → ClO + O₂.

21. Enumerate the damage - to humans, animals and plants caused due to ozone depletion.
Answer: Humans & Animals: Causes sunburn, skin cancer, aging of the skin, eye cataract, weakening of the immune system, and severe damage to animal cells. Plants: Retards plant growth, inhibits pollen germination, reduces chlorophyll content, and disrupts ecosystems.

22. State the main chemical - which are responsible for more than 80% ozone depletion. State the man-made applications which make use of that chemical.
Answer: The main chemicals are Chlorofluorocarbons [CFCs]. Man-made applications include aerosol sprays, coolants in refrigeration & A.C's, dry cleaning fluids, and cleansing agents for electronic components.

23. State the role - of chlorofluorocarbons in ozone destruction or depletion [no equations required].
Answer: CFCs are broken down by U.V. radiations in the stratosphere to release active free radicals like atomic chlorine. These chlorine radicals initiate and catalyse a chain reaction capable of breaking down over 100,000 ozone molecules, leading to severe ozone depletion.

24. Enumerate methods - of protecting the ozone layer and preventing its depletion.
Answer: Methods include replacing CFC products with safer alternative products (like HCFCs), initiating CFC-free labelling on products, and enforcing International Treaties like the Montreal Protocol to prevent ozone depletion.

25. Enumerate - the main substances present in water, which are (a) beneficial to life (b) harmful to life. State - the adverse effects of - 'minomata' disease.
Answer: (a) Beneficial: Dissolved oxygen and essential minerals in traces like Calcium, Potassium, Zinc, and Copper. (b) Harmful: Toxic heavy metals (mercury & lead), industrial chemical wastes (benzene), polymers (plastics), agricultural wastes (pesticides), and biological pathogens. Minamata disease causes severe sensory disturbances, lack of coordination, and hearing & speech impairment.

Multiple Choice Questions [MCQs] - Select the correct answer

1. A source which releases a foul smelling gas - which is oxidised to a pollutant, which causes acid rain.
(a) Smelting plants     (b) Internal combustion engines
(c) Organic matter on bacterial decomposition     (d) Sulphuric acid plants
Answer: (c) Organic matter on bacterial decomposition

2. The pH of acid rain on pH scale is -
(a) Less than (b) More than (c) Same as - pH of natural rain water (d) More than - pH of pure water
Answer: (a) Less than

3. The main natural source of carbon dioxide contributing to global warming is -
(a) Power plants (b) Bacterial decay of vegetable matter (c) Exhaust from automobiles (d) Burning of fossil fuels
Answer: (b) Bacterial decay of vegetable matter

4. The atmospheric pollutant which contributes to both - ozone depletion & global warming.
(a) Carbon tetrachloride (b) Methane (c) Carbon dioxide (d) Bromofluorocarbon
Answer: (d) Bromofluorocarbon

5. Photodissociation reaction involves the conversion -
(a) O₂ → O₃     (b) O₃ → O₂ + [O]     (c) O₃ → 2O₂     (d) O₂ → 2[O]
Answer: (d) O₂ → 2[O]

6. Assertion (A) : Green house effect results in rise in atmospheric temperature & has a global impact.
Reason (R) : Promoting aforestation helps in absorbing green house gas - i.e. CO₂ during photosynthesis.
(a) Both A & R are true - and R is the correct explanation of A.     (c) A is true - but R is false
(b) Both A & R are true - but R is not the correct explanation of A.     (d) A is false - but R is true.
Answer: (b) Both A & R are true - but R is not the correct explanation of A.

High Order Thinking Questions

1. State why - natural rain water produced in an unpolluted atmosphere, is slightly acidic. Give a balanced equation of the same.
Answer: It is slightly acidic because the CO₂ present in traces in unpolluted air dissolves in rain water forming weak carbonic acid [H₂CO₃]. Equation: H₂O + CO₂ → H₂CO₃.

2. 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: When organic matter undergoes bacterial decomposition, it releases H₂S which is oxidised to SO₂. Equation: 2H₂S + 3O₂ → 2H₂O + 2SO₂.

3. State why - high temperatures in internal combustion engines release pollutant - oxides of nitrogen.
Answer: Because the nitrogen in the air drawn from the atmosphere combines with oxygen only at high temperatures (above 1300°C) achieved in internal combustion engines, producing nitrogen monoxide.

4. State the impact - of global warming on the countries economy.
Answer: Global warming indirectly hurts the economy by causing large-scale destruction of ecosystems, coastal flooding & erosion due to rising sea levels, and agricultural disruption by affecting soil fertility and the life cycle of crops.

5. Differentiate between - global warming & climate change.
Answer: Global warming refers specifically to the rise in atmospheric temperatures globally due to the greenhouse effect. Climate change refers to the subsequent shifts in weather patterns caused by this warming, such as tropical regions experiencing more rainfall and northern latitudes experiencing shorter, wetter winters.

6. State why - global warming & ozone depletion are directly or indirectly - interconnected.
Answer: They are interconnected because certain man-made chemical pollutants, particularly Chlorofluorocarbons (CFCs), act both as potent greenhouse gases that contribute to global warming and as the primary catalysts that break down and destroy the ozone layer.

7. Give a reason why - ozone holes occur in the antartic & more so during spring.
Answer: Ozone holes, which are severe depletions of the ozone layer, are notably seen above the Antarctic region in spring because stratospheric wind circulation transports ozone towards the poles, and unique extreme cold conditions combined with returning spring sunlight accelerate CFC breakdown cycles.

8. How can the causes - of acid rain & ozone depletion be compared.
Answer: Both are primarily caused by anthropogenic (man-made) emissions. Acid rain is caused by burning fossil fuels releasing oxides of sulphur and nitrogen. Ozone depletion is caused by industrial and commercial release of halocarbon chemicals like CFCs.

9. State how the effects - of acid rain & green house gases are related.
Answer: Acid rain retards plant growth and destroys forests. Since forests act as a major natural sink for absorbing the greenhouse gas CO₂, the destruction of plant life by acid rain indirectly increases the concentration of greenhouse gases in the atmosphere, accelerating global warming.

10. Compare the advantage - of the green house effect over its disadvantage.
Answer: Advantage: The natural greenhouse effect is crucial for life as it maintains a warm surface temperature on earth by trapping essential heat. Disadvantage: An enhanced greenhouse effect due to excess pollutants leads to excessive global warming, which melts ice caps and causes disastrous climate changes.

11. State how - water vapour contributes to the green house effect.
Answer: Water vapour acts as a greenhouse gas in the atmosphere; it effectively absorbs the long-wave thermal infra-red radiation emitted from the earth, preventing it from escaping into space and thereby contributing to the blanketing effect.

12. State why - acid rain is a regional problem, while global warming a global problem.
Answer: Acid rain is regional because the pollutants (SO₂ and NO₂) mix with local moisture and fall back to the earth in areas generally near the pollution sources. Global warming is a global problem because greenhouse gases disperse evenly throughout the earth's atmosphere, raising temperatures globally regardless of where they were emitted.

3. TEST - HIGH ORDER & CRITICAL THINKING QUESTIONS

UNIT TEST PAPER - 8

Q.1 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
Answer: B: Sulphur dioxide

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

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

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

Q.2 Give balanced equations for the following conversions [one or two steps].

1. Sulphur trioxide to sulphuric acid - a constituent of acid rain.
Answer: H₂O + SO₃ → H₂SO₄ [aq.]

2. Nitrogen to nitrogen dioxide - in an internal combustion engine.
Answer:
Step 1: N₂ + O₂ → 2NO
Step 2: 2NO + O₂ → 2NO₂

3. Methane to carbon dioxide - a green house gas.
Answer: CH₄ + 2O₂ → CO₂ + 2H₂O + Δ

4. A molecule of ozone to two molecules of oxygen gas.
Answer: O₃ + [O] → 2O₂

5. Oxygen to ozone gas by photolysis.
Answer:
Step 1: O₂ → (U.V. light) → [O] + [O]
Step 2: O₂ + [O] → O₃

Q.3 Give reasons for the following.

1. Natural rain water does not have a pH of 7 [i.e. neutral]
Answer: Because the CO₂ present in traces in unpolluted air dissolves in rain water forming weak carbonic acid, making it slightly acidic.

2. A catalytic converter in an internal combustion engine reduces pollution.
Answer: Because the reduction catalyst [Pt/Pd] separates the nitrogen atom from harmful NO and NO₂ molecules, freeing oxygen and releasing harmless nitrogen gas.

3. In absence of green house gases the surface temperature of the earth is maintained.
Answer: Because a balance is maintained between the heat energy absorbed by the earth from solar radiation and the thermal infra-red radiation emitted back from the earth into the atmosphere.

4. The formation of ozone involves a chemical reaction called photolysis.
Answer: Because highly energetic ultraviolet radiations from the sun (light) are required to break the oxygen molecule [O₂] into two reactive oxygen atoms [O].

5. Destruction of ozone layer is harmful for both humans & plants.
Answer: Because it allows harmful U.V. radiations to reach the earth, which causes sunburn, skin cancer and cell damage in humans, and retards plant growth and inhibits pollen germination in plants.

Q.4 Name or state the following :

1. An atmospheric pollutant produced during lightening discharge.
Answer: Oxides of nitrogen

2. A form of wet deposition of acid rain other than rain water.
Answer: Snow (or fog / dew)

3. An atmospheric pollutant responsible for both global warming & ozone depletion.
Answer: Chlorofluorocarbons [CFCs]

4. A green house gas which contains carbon & hydrogen only.
Answer: Methane [CH₄]

5. The atom which reacts with oxygen to form ozone.
Answer: Atomic oxygen [O]

Q.5 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.
Answer: Decreases

2. The acidity of the soil.
Answer: Increases

3. The fertility of the soil.
Answer: Decreases

4. The pH of water bodies.
Answer: Decreases

5. The rate of photosynthesis in plants.
Answer: Decreases

Q.6 The diagram represents the green house effect.

1. State why the effect is called 'global warming'.
Answer: The effect is called 'global warming' because the greenhouse effect results in a rise in atmospheric temperatures which is not confined to one region but has a global impact.

2. Name a process which a] releases b] absorbs - green house gas - CO₂.
Answer: a] Respiration (or combustion of fossil fuels) b] Photosynthesis (by plants & forests).

3. State an advantage of use of C.N.G. over combustion of fossil fuels.
Answer: C.N.G. causes minimum pollution, does not contain lead, and lowers maintenance cost as compared to other fossil fuels.

4. Which of the following - biofertilizers or nitrogenous fertilizers reduces the green house gas - CO₂. Explain.
Answer: Biofertilizers help reduce greenhouse gases. Checking deforestation and using biofertilizers instead of nitrogenous fertilizers helps control the emission of nitrous oxide (a greenhouse gas). Moreover, promoting plant growth (which biofertilizers support) safely absorbs CO₂.

5. Does the sea level rise or fall due to global warming. Explain.
Answer: The sea level rises. Global warming increases the melting of ice-caps, resulting in a rise in sea levels, coastal flooding, and erosion.