Class 9 Chapter 10: Environmental Chemistry, Free Notes

These are the free notes for Class 9 Chapter 10 Chemistry. Exercise short questions, CRQs, and internal short questions are included. It is about Environmental Chemistry, written by Sir Umair Khan.

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1. Which gases are responsible for the greenhouse effect?

(a) SO₂, NO₂ (b) NO₂, CO (c) CO₂, CH₄ (d) O₂, N₂

2. Indicate the source of sulphur which is responsible for the presence of oxides of sulphur in the atmosphere.

(a) Decomposition of vegetation

(b) Waste gases from digestion of animals

(d) Combustion of fossil fuels

3. Concentration of which gas in the atmosphere is decreased by photosynthesis in plants?

(a) Oxygen (b) Nitrogen (c) Carbon dioxide (d) Water vapours

4. Which substance remains unaffected in the catalytic converter fixed in the exhaust of the automobiles?

(a) CO₂ (b) CO (c) NO (d) NO₂

5. People of which age groups are most affected by air pollution?

(a) Young adults (b) Middle-aged people (c) Children (d) Both children and aged people

6. In which area is there a greater possibility of acid rain?

(a) Around villages (b) Around big cities (c) Around industrial areas (d) Around water bodies

7. Why is smog not felt in summer?

(a) Because fog is not present in summer

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

(d) Because less fossil fuels are burnt in summer

8. Which catalyst is used in the catalytic converter fixed in the exhaust systems of automobiles?

(a) Ni (b) Cu (c) Pt, Pd and Rh (d) CaO

9. Which components are essential for the formation of photochemical smog?

(a) CO, NO₂, CO₂

(b) NO₂, volatile organic compounds, sunlight

(d) Volatile organic compounds, NO₂, CO

10. Which gases contribute towards the formation of acid rain?

(a) Oxides of carbon (b) Oxides of sulphur (c) Oxides of nitrogen (d) Both the oxides of nitrogen and sulfur

Short Questions & Answers

i. What is the main objective of environmental education?

Answer: The main objective of environmental education is to raise awareness of environmental problems and teach people how to protect and preserve nature.

ii. How is particulate matter released in the atmosphere?

Answer: Particulate matter is released through human activities like burning fossil fuels, vehicular emissions, and industrial processes, as well as natural sources like wildfires and volcanic eruptions.

iii. Which gas is more poisonous, carbon dioxide or carbon monoxide?

Answer: Carbon monoxide (CO) is much more poisonous than carbon dioxide (CO₂) because it stops red blood cells from carrying oxygen, leading to suffocation and death.

iv. How does acid rain affect forests?

Answer: Acid rain damages tree leaves, reduces photosynthesis, washes away essential nutrients from the soil, and retards forest growth.

v. In what way sulphur present in fossil fuels becomes dangerous?

Answer: When fossil fuels containing sulfur are burned, they release sulfur dioxide gas (SOx₎, which causes eye irritation, breathing difficulties, and combines with air moisture to form harmful acid rain.

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

Answer:

Burning of fossil fuels (coal, oil, and natural gas).
Deforestation (cutting down forests).
Industrial activities and waste decomposition releasing gases like methane.

vii. How is wind energy useful for us?

Answer: Wind energy is a clean, renewable resource used to generate electricity without releasing harmful air pollutants or greenhouse gases.

Constructed Response Questions (CRQs) & Answers

i: How is the excessive use of insecticides and pesticides harmful for birds?

Answer: Insecticides and pesticides sprayed on crops enter the natural food chain. Birds consume contaminated insects or seeds, causing these toxic chemicals to accumulate in their bodies. This weakens their health and causes eggshell thinning, leading to broken eggs before hatching and reducing bird populations.

ii: The percentage of carbon dioxide in the air is only 0.04%. Then how does it become harmful for the ecosystem?

Answer: Even at 0.04%, carbon dioxide (CO₂) acts as a strong greenhouse gas that traps thermal radiation. Increased emissions from burning fuels and deforestation add extra CO₂, which traps more heat, leading to global warming, climate change, and melting ice caps.

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

Answer: Greenhouse gases (like CO₂ and CH₄) have molecular structures capable of absorbing long-wave infrared (heat) radiation re-emitted by the Earth. Gases like nitrogen (N₂) and oxygen (O₂) cannot absorb heat radiation, so they do not cause the greenhouse effect.

iv: How can you reduce the emission of carbon monoxide present in the gases emitted by the burning of fuels in automobile engines?

Answer:
- Catalytic Converters: Installing catalytic converters in vehicle exhausts converts toxic carbon monoxide into harmless carbon dioxide before emission.
- Engine Tuning: Maintaining and tuning automobile engines regularly ensures complete fuel combustion, minimizing carbon monoxide production.

v: Mention three different ways in which solar energy can be useful for us.

Answer:
1. Electricity Generation: Photovoltaic solar panels convert sunlight directly into electricity for homes and factories.
2. Thermal Heating: Solar water heaters use the sun’s warmth to heat water for domestic use.
3. Clean Power Source: Using solar energy reduces reliance on fossil fuels, directly lowering air pollution and greenhouse gas emissions.

Additional Short Questions

How does acid rain affect soil?
Acid rain washes away essential nutrients required for plant growth and retards plant development.
Why does acid rain appear clean but is harmful?
It looks like normal rain because the dissolved acids (sulfuric acid and nitric acid) are clear and invisible, yet chemically destructive.
What is an air pollutant?
Any harmful substance introduced into the atmosphere that damages living organisms or the environment.
Name any two pollutants released due to incomplete combustion of fuels.
Carbon monoxide (CO) and soot or particulate matter.
Why do only some pollutant gases present in the atmosphere cause the greenhouse effect while others do not?
Only gases with flexible molecular structures (like CO2 and CH4) absorb infrared radiation, while symmetric gases (like N2 and O2) cannot.
What is the Air Quality Index (AQI)?
AQI is a standardized scale used to measure and report the daily cleanliness or pollution level of the air.
How do greenhouse gases cause global warming?
They absorb long-wave infrared radiation re-emitted by the Earth, trapping heat and raising global average temperatures.
Name two famous monuments affected by acid rain.
The Taj Mahal in India and the Parthenon in Greece.
In what way does sulfur (S) present in fossil fuels become dangerous?
When burned, it forms sulfur dioxide gas (SOx), which causes eye irritation, breathing difficulties, and combines with air moisture to form acid rain.
How does sulfur dioxide contribute to air pollution?
It acts as a primary toxic air pollutant, causing respiratory issues, and reacts with atmospheric water vapor to produce acid rain.
How is the excessive use of insecticides and pesticides harmful for birds?
Pesticides enter the food chain via contaminated prey, accumulate in bird bodies, weaken their internal systems, and cause eggshell thinning.
What are the harmful effects of acid rain on human health?
It indirectly harms health by releasing toxic metals into drinking water and causing severe respiratory issues like asthma.
Why does smog form more in winter?
Fog is present in winter to trap smoke, whereas in summer, high temperatures prevent fog formation and cause air/smoke to rise.
How does methane contribute to global warming?
Methane traps thermal radiation effectively in the atmosphere, increasing the overall greenhouse effect.
What happens to the soil if trees are destroyed by acid rain?
The soil loses essential nutrients, becomes more acidic, and suffers from increased vulnerability to erosion.
How can you reduce the emission of CO2 present in the gases emitted by the burning of fuel in automobile engines?
Switch to fuel-efficient vehicles, use alternative clean energy, and maintain proper engine tuning to reduce overall fuel consumption.
What is the atmosphere?
The layer of gases surrounding the Earth that protects life and maintains environmental conditions.
Why are N95 masks more effective against air pollution?
N95 masks are specifically designed to filter out at least 95% of airborne particles, including fine particulate matter (PM2.5).
How does cutting trees affect the greenhouse effect?
It reduces the removal of carbon dioxide via photosynthesis, causing more CO2 to remain trapped in the air.
What is the role of photosynthesis in reducing air pollution?
Photosynthesis in plants decreases the concentration of carbon dioxide (CO2) in the atmosphere.
How do air pollutants enter the human bloodstream?
Inhaled pollutant gases (like carbon monoxide) pass through the lungs into tiny blood vessels, binding with blood components like hemoglobin.
What gas is given off by rotting garbage?
Methane gas (CH4) is produced in places where organic matter is rotting or decomposing.
Why is wind energy considered a clean energy source?
It produces power naturally using wind without burning fuels or releasing harmful waste gases.
How do air pollutants affect the lungs?
Pollutants irritate the airways, reduce lung capacity, trigger asthma attacks, and cause chronic respiratory illnesses.
What is flue gas desulfurization?
A technology used to remove sulfur dioxide (SO₂) from exhaust gases of fossil-fuel power plants.
Which gas is more poisonous, CO or CO₂?
Carbon monoxide (CO) is much more poisonous because it directly prevents blood from carrying oxygen.
What is the estimated weight of the Pacific Ocean garbage patch?
Approximately 80,000 metric tons.
How does acid rain affect forests?
It damages tree leaves, reduces photosynthesis, washes away soil nutrients, and retards forest growth.
What percentage of marine mammals are at risk of choking due to plastic?
Studies estimate around 10% to 15% directly suffer from ingestion or choking risks out of total impacted species.
Why do areas with more factories have higher pollution levels?
Factories continuously burn large amounts of fuel and release concentrated chemical exhaust gases.
What gas is naturally radioactive and increases the risk of lung cancer indoors?
Radon gas.
What are the benefits of solar energy?
Generates clean electricity via solar panels, provides solar thermal heating for domestic water, and reduces reliance on polluting fossil fuels.
Who is known as the “Father of Acid Rain”?
Robert Angus Smith.
How does global warming affect agriculture?
It alters natural weather patterns, causes droughts or unseasonal floods, and disrupts crop growth cycles.
Why is planting trees important in reducing air pollution?
Trees absorb carbon dioxide during photosynthesis and trap particulate matter on their leaves.
Major Pakistani cities experience a very high AQI in winter, which renders them the most polluted cities in the world. Point out some of the major causes of high AQI in these cities.
Crop residue burning in fields, heavy unmaintained vehicular traffic, industrial fuel emissions, and winter temperature inversions that trap pollutants near the ground.
How does acid rain travel long distances from its source?
Air pollutants (SO2 and NOx) are carried high into the atmosphere by wind currents before combining with moisture and falling as acid rain far away.
What are the effects of global warming on sea levels?
It causes polar ice caps to melt and seawater to thermally expand, raising global sea levels.
How does global warming cause extreme weather events?
Higher global temperatures disrupt atmospheric pressure, global wind patterns, and ocean evaporation rates.
How can acid rain damage historical buildings and monuments?
The acid chemically reacts with and corrodes limestone, marble, and metal structures.
What is the main objective of environmental education?
To create awareness among people about environmental problems and teach them how to protect and preserve nature.
Why is carbon monoxide considered a toxic gas?
It binds tightly to blood hemoglobin, blocking oxygen transport, which causes suffocation and can lead to death.
Why do some plants benefit from global warming while others do not?
Higher CO2 levels can boost growth for certain plants, but excessive heat and drought stress harm others.
What percentage of air is nitrogen?
Nitrogen makes up approximately 78% of the atmosphere.
What is meant by photochemical smog?
A type of air pollution formed when volatile organic compounds and nitrogen oxides react in the presence of sunlight.
Mention three different ways in which solar energy can be useful for us.
Generating electricity through solar panels, heating water via solar thermal systems, and reducing reliance on fossil fuels.
How does carbon monoxide affect human health?
It stops red blood cells from carrying oxygen throughout the body, causing headaches, unconsciousness, and suffocation.
Define the greenhouse effect.
The process where atmospheric gases absorb infrared radiation emitted by the Earth’s surface and trap heat.
At what time of the day is humidity maximum?
Early morning around sunrise.
How is wind energy useful for us?
It is a clean, renewable resource that generates electricity without producing air pollutants or greenhouse gases.
What are the effects of acid rain on aquatic life?
It makes water bodies highly acidic, which kills fish eggs and harms aquatic organisms.
How does industrialization contribute to environmental pollution?
By releasing large amounts of waste gases (SOx, NOx, CO2), industrial effluents, and solid pollutants into nature.
Name the major sources of air pollution.
Burning fossil fuels in vehicles and factories, rapid deforestation, industrial emissions, and natural events like wildfires.
What is the role of a carbon monoxide detector?
To sound an alarm when elevated levels of toxic carbon monoxide gas are detected in an indoor space.
How does air pollution reduce the quality of life?
It causes chronic health problems, degrades environmental surroundings, and restricts outdoor physical activities.
How do catalytic converters reduce air pollution?
They use precious metal catalysts (platinum, palladium, rhodium) to convert harmful exhaust gases like CO into harmless CO2 before emission.
Where is the largest garbage patch in the world located?
In the North Pacific Ocean (the Great Pacific Garbage Patch).
How does acid rain form?
Sulfur dioxide (SO2) and nitrogen oxides (NOx) react with water vapor and oxygen in the air to form sulfuric acid and nitric acid.
Why is reducing fossil fuel consumption important for the environment?
It directly decreases the release of toxic gases (CO, SOx, NOx) and greenhouse gases (CO2), lowering pollution and global warming.
Percentage of CO2 in air is only 0.04%. Then, how does it become harmful for the ecosystem?
It is a strong heat-trapping gas; excess emissions trap extra thermal radiation, causing global climate change and sea-level rise.
What is acid rain?
Rain made acidic by dissolved atmospheric pollutants like sulfuric acid and nitric acid, typically having a pH of 4.2 to 4.4.
How does global warming affect summers and winters?
It makes summers longer and hotter while causing erratic, unpredictable weather patterns in winter.
What is the role of water vapor in the greenhouse effect?
Water vapor acts as a natural greenhouse gas that absorbs infrared heat radiation, helping maintain Earth’s thermal warmth.
How does methane emissions contribute to air pollution?
Methane (CH4) is a strong greenhouse gas that traps thermal radiation in the atmosphere, directly contributing to global warming.
Why do greenhouse gases trap heat but not sunlight?
Their molecular structure allows short-wave sunlight to pass through, but absorbs long-wave infrared heat radiation re-emitted by Earth.
What precautions should be taken when air quality is bad?
Wear N95 masks, avoid outdoor exercise, and use indoor air purifiers.
How many trees are cut daily to make toilet paper?
Approximately 27,000 trees per day worldwide.
Why is acid rain harmful to plants?
It destroys leaf surfaces, lowers photosynthesis, and removes essential nutrients from the soil.
How do living organisms contribute to carbon dioxide levels in the air?
Living organisms release carbon dioxide into the air during respiration.
Name any three major sources responsible for the greenhouse effect.
Burning fossil fuels, deforestation, and industrial waste emissions.
Name the major gases present in the air.
Nitrogen (N2), Oxygen (O2), Carbon dioxide (CO2), and Argon (Ar).
How can the emission of sulfur dioxide be reduced?
By using low-sulfur fuels and implementing flue gas desulfurization in industrial chimneys.
In which unit is the concentration of air pollutants measured?
Micrograms per cubic meter (µg/m³) or parts per million (ppm).
How has climate change affected Pakistan during the last five years?
It has caused severe flood events, heatwaves, unpredictable rainfall shifts, and intense winter smog episodes.
Which gas is released when a carbonated drink is opened?
Carbon dioxide (CO2).
How does the composition of air vary?
It varies based on location, industrial activity, atmospheric moisture content, and altitude.
Name the gases responsible for acid rain.
Sulfur dioxide (SO2) and nitrogen oxides (NOx).
Who is most vulnerable to air pollution?
Both children and aged people are the most affected by air pollution.
How do particulate matter (PM) released into the atmosphere?
Through vehicle emissions, fuel combustion, industrial processes, and natural dust or wildfires.
What gas is produced by rice fields that contributes to global warming?
Methane gas (CH4).
Define air pollution.
The contamination of air by harmful chemical species, particulate matter, or biological materials that negatively impact living things.
Name two renewable energy sources that help reduce pollution.
Solar energy and wind energy.
Why do some cities experience more smog than others?
Cities with higher industrial density, heavy traffic, and basin-like geographical layouts trap more fog and smoke.
What are the three functions of a catalytic converter?
It converts carbon monoxide into carbon dioxide, converts nitrogen oxides into harmless gases, and reduces overall exhaust emissions.
Why does global warming cause an increase in sea levels?
It melts polar ice caps and glaciers while causing seawater to expand as it warms up.
How does acid rain indirectly affect human health?
It leaches toxic heavy metals (like aluminum or lead) from soil into drinking water supplies and crop chains.
What does an AQI over 300 indicate?
An AQI over 300 indicates hazardous air quality levels that pose severe health risks to the population.
How do oxides of nitrogen form in car engines?
High temperatures during fuel combustion force atmospheric nitrogen (N2) and oxygen (O2) to react together.
What is considered a good AQI value?
An AQI value between 0 and 50 is considered good.
Why does AQI not rise in Pakistan in hot days of summer?
Fog is absent in summer, and intense heat causes warm air and pollutants to rise rapidly into higher atmospheric layers.
What is the role of carbon dioxide in global warming?
It traps long-wave heat radiation re-emitted by the Earth, increasing average atmospheric temperatures.
How much water is available for human use?
Less than 1% of the Earth’s total water is readily available fresh water for human use.
Name the main greenhouse gases.
Carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapor.
Why are some gases more harmful to human health than others?
Because certain gases (like carbon monoxide) react chemically with human blood and tissue, whereas non-reactive gases do not.