Class 9 Chemistry Notes – Chapter 10

Environmental Chemistry

1. Tick (✓) the Correct Answer

(i) Which gases are responsible for the greenhouse effect?

Answer: (c) CO₂, CH₄

(ii) Indicate the source of sulphur which is responsible for the presence of oxides of sulphur in the atmosphere.

Answer: (d) Combustion of fossil fuels

(iii) Concentration of which gas in the atmosphere is decreased by photosynthesis in plants?

Answer: (c) Carbon dioxide

(iv) Which substance remains unaffected in the catalytic converter fixed in the exhaust of automobiles?

Answer: (a) CO₂

(v) People of which age groups are most affected by air pollution?

Answer: (d) Both children and aged people

(vi) In which area is there a greater possibility of acid rain?

Answer: (c) Around industrial areas

(vii) Why is smog not felt in summer?

Answer: (b) Because, due to the heat of the Earth, smoke rises up

(viii) Which catalysts are used in the catalytic converter fixed in the exhaust systems of automobiles?

Answer: (c) Pt, Pd and Rh

(ix) Which components are essential for the formation of photochemical smog?

Answer: (b) NOₓ, volatile organic compounds, and sunlight

(x) Which gases contribute towards the formation of acid rain?

Answer: (d) Both the oxides of nitrogen and sulphur

2. Questions for Short Answers

(i) What is the main objective of environmental education?

Answer: The main objective of environmental education is to raise awareness and build knowledge regarding ecological protection, pollution control, sustainable resource use, and individual responsibility in preserving environmental health.

(ii) How is particulate matter released into the atmosphere?

Answer: Particulate matter is released into the atmosphere through natural sources, such as dust storms, volcanic eruptions, and forest fires, and human activities, such as industrial processes, vehicle exhaust, construction and demolition, and the burning of fossil fuels and biomass.

(iii) Which gas is more poisonous, CO₂ or CO?

Answer: Carbon monoxide (CO) is far more poisonous than carbon dioxide (CO₂) because it binds strongly to haemoglobin in red blood cells, reducing the blood’s ability to transport oxygen to body tissues and potentially causing suffocation.

(iv) How does acid rain affect forests?

Answer: Acid rain damages forests by removing essential nutrients, such as calcium and magnesium, from the soil. It can also release toxic aluminium ions that damage tree roots and weaken leaves and needles, making trees more vulnerable to diseases and pests.

(v) In what way does sulphur present in fossil fuels become dangerous?

Answer: Sulphur present in fossil fuels burns during combustion to form sulphur dioxide (SO₂). This gas is released into the atmosphere, where it undergoes oxidation and reacts with water and other substances to form acids, contributing to acid rain and respiratory illnesses.

(vi) Name any three major sources responsible for the greenhouse effect.

Answer:

1. Combustion of fossil fuels in vehicles and power plants, releasing CO₂.

2. Agricultural activities, such as livestock rearing and paddy cultivation, releasing CH₄.

3. Deforestation, which reduces the absorption of CO₂ by plants.

(vii) How is wind energy useful for us?

Answer: Wind energy is a clean, renewable, and inexhaustible source of power. It generates electricity through wind turbines without directly producing greenhouse gases, air pollutants, or toxic waste during operation.

3. Constructed Response Questions

(i) How is the excessive use of insecticides and pesticides harmful to birds?

Answer: Insecticides and pesticides accumulate in insects and plants consumed by birds. Through biomagnification, the concentrations of certain toxic chemicals increase along the food chain. These chemicals can cause reproductive failure, such as eggshell thinning, nervous system damage, and death in birds.

(ii) The percentage of CO₂ in air is only 0.04%. Then how does it become harmful to the ecosystem?

Answer: Although CO₂ is present in a small proportion, it is an important greenhouse gas. An increase in its atmospheric concentration enhances the trapping of outgoing infrared radiation from the Earth, contributing to global warming and climate change.

(iii) Why do only some pollutant gases present in the atmosphere cause the greenhouse effect while others do not?

Answer: Greenhouse gases, such as CO₂, H₂O, CH₄, and N₂O, can absorb and re-emit infrared radiation. In contrast, symmetrical diatomic gases, such as N₂ and O₂, do not significantly absorb infrared radiation because their molecular vibrations do not produce the required change in dipole moment. Therefore, they do not contribute significantly to the greenhouse effect.

(iv) How can you reduce the emission of CO in the gases produced by burning fuel in automobile engines?

Answer: Carbon monoxide emissions can be reduced by ensuring efficient combustion through proper engine tuning, maintaining the correct air-fuel ratio, regularly servicing vehicles, and installing efficient catalytic converters in automobile exhaust systems.

(v) Mention three different ways in which solar energy can be useful to us.

Answer:

1. Generating electricity using photovoltaic (solar) cells.

2. Heating water for domestic and industrial use through solar water heaters.

3. Providing natural heating and lighting for buildings through passive solar design.

4. Descriptive Questions

(i) Describe the harmful effects of the major pollutants present in the air.

Answer:

• Carbon Monoxide (CO): Reduces the oxygen-carrying capacity of blood, causing headaches, dizziness, and damage to the heart and brain.

• Sulphur Dioxide (SO₂): Irritates the respiratory tract, can worsen respiratory diseases, and contributes to acid rain.

• Nitrogen Oxides (NOₓ): Contribute to photochemical smog, irritate the lungs, and damage vegetation.

• Particulate Matter (PM): Can penetrate deep into the lungs, contributing to asthma, cardiovascular diseases, and reduced visibility.

(ii) Explain the greenhouse effect. How is global warming dangerous for us?

Answer:

Greenhouse Effect: The greenhouse effect is the natural process in which greenhouse gases in the atmosphere absorb and re-emit infrared radiation from the Earth’s surface, keeping the planet warm enough to support life.

Dangers of Global Warming:

1. Melting of polar ice caps and glaciers.

2. Rising sea levels, causing coastal flooding.

3. Changes in climate patterns that affect agriculture.

4. Increased frequency and intensity of extreme weather events, such as heatwaves, droughts, and severe storms.

(iii) What is the Air Quality Index (AQI)? What information does it convey?

Answer: The Air Quality Index (AQI) is a numerical scale used by government agencies to communicate how polluted the air is or how polluted it is forecast to become. It conveys the potential health risks associated with major air pollutants, such as PM₂.₅, PM₁₀, NO₂, SO₂, CO, and O₃. AQI categories, often represented by colours, indicate different levels of pollution and associated health risks.

(iv) Who are high-risk groups, and why is pollution more dangerous for them?

Answer: High-risk groups include children, elderly people, pregnant women, and individuals with pre-existing respiratory or cardiovascular conditions, such as asthma and heart disease. Air pollution is more dangerous for them because their respiratory or cardiovascular systems may be developing, weakened, or already compromised, making them more vulnerable to harmful pollutants.

(v) Describe three strategies to address environmental issues.

Answer:

1. Transition to Renewable Energy: Replacing fossil fuels with wind, solar, and hydroelectric power to reduce greenhouse gas and air pollutant emissions.

2. Strict Environmental Regulations and Enforcement: Implementing laws that control industrial emissions, establish vehicle emission standards, and prevent illegal waste dumping.

3. Promotion of a Circular Economy and Green Practices: Encouraging recycling, waste reduction, afforestation, green chemistry, and sustainable agricultural techniques.

5. Investigative Questions

(i) Major Pakistani cities experience a very high AQI in winter, making them among the most polluted cities in the world. Point out some of the major causes of high AQI in these cities.

Answer: High winter AQI levels in Pakistani cities are caused by several factors, including temperature inversions that trap cold, stagnant air near the ground; crop residue burning; vehicle exhaust, particularly from poorly maintained vehicles; brick kiln emissions; industrial activities; construction dust; and the burning of solid fuels and biomass for heating. These pollutants accumulate in the atmosphere, increasing smog and worsening air quality.

(ii) Why does AQI not rise in Pakistan on hot summer days?

Answer: AQI can also rise during summer, so it does not remain low on all hot days. However, strong solar heating can promote vertical air movement and atmospheric mixing, helping disperse some pollutants. In winter, temperature inversions and stagnant air can trap pollutants near the ground, often causing severe smog. Summer air quality can still deteriorate due to dust, vehicle emissions, industrial pollution, and the formation of ground-level ozone.

(iii) How has climate change affected Pakistan during the last five years?

Answer: During the past five years, Pakistan has experienced serious impacts associated with climate change, including catastrophic flooding, particularly the 2022 monsoon floods; glacial lake outburst floods (GLOFs) in northern regions; intense heatwaves; drought conditions in some agricultural areas; and changing rainfall patterns. These events have damaged homes, infrastructure, and crops, affected water availability, caused displacement, and created major economic and social challenges.

Notes by Sir Dilawar

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