ChemistryICSE Class 9 · Chapter 8

Atmospheric and Environmental Chemistry ICSE Class 9: Acid Rain, Global Warming, Ozone and Water Pollution

Updated 15 October 2026 · Fact-checked

Acid rain forms when oxides of sulphur and nitrogen from fuels and engines dissolve in rainwater as sulphuric and nitric acids. Greenhouse gases such as carbon dioxide and methane trap heat, causing global warming. CFCs destroy the ozone layer, and heavy metals such as mercury poison water, as in Minamata disease.

What Atmospheric and Environmental Chemistry is about

Human activity changes the chemistry of the air and water around us. Burning fuels adds acidic oxides and carbon dioxide to the air; some chemicals thin the ozone layer; industry, farming and sewage put harmful substances in water.

The CISCE 2028 syllabus (Class IX, topic 8) covers: acid rain (composition, cause, impact; oxides of sulphur from sulphur in fossil fuels; oxides of nitrogen from high temperatures in furnaces and engines, with equations; effects on soil and water bodies); global warming (greenhouse gases water vapour, carbon dioxide, methane and oxides of nitrogen, their sources and ways to reduce them); ozone depletion (formation of ozone with equations, its functions, and the chemicals that destroy it, named only); and water pollution (substances in water that are beneficial, such as dissolved oxygen and minerals, and harmful, such as toxic heavy metals with special mention of Minamata disease, plastics, sewage and pesticides).

Weightage: CISCE publishes no chapter weightage for ICSE Chemistry. Atmospheric and Environmental Chemistry is topic 8 of the Class IX part of the 2028 syllabus; the Class IX paper (80 marks, 2 hours) is set and marked by the school.Source: CISCE ICSE Chemistry (Science Paper 2) syllabus, examination year 2028 (Class IX)

Key concepts

Acid rain: cause and composition

Normal rain is slightly acidic (pH about 5.6) because it dissolves a little carbon dioxide. Acid rain has a pH below 5.6, mainly because of sulphuric acid and nitric acid (with some sulphurous and nitrous acids).

Oxides of sulphur: coal and petroleum contain sulphur. When burnt:
$S + O_{2} \to S O_{2}$
In the air, sulphur dioxide is slowly oxidised (helped by sunlight and dust) and dissolves in rain:
$2 S O_{2} + O_{2} \to 2 S O_{3}$
$S O_{3} + H_{2} O \to H_{2} S O_{4}$
$S O_{2} + H_{2} O \to H_{2} S O_{3}$

Oxides of nitrogen: at the very high temperatures in furnaces, power stations and internal combustion engines (and in lightning), nitrogen and oxygen of the air combine:
$N_{2} + O_{2} \to 2 N O$
$2 N O + O_{2} \to 2 N O_{2}$
$4 N O_{2} + 2 H_{2} O + O_{2} \to 4 H N O_{3}$

Worked example

Write the equations showing how sulphur in coal leads to sulphuric acid in rain.

Try it first, then show the solutionSolution

$S + O_{2} \to S O_{2}$
$2 S O_{2} + O_{2} \to 2 S O_{3}$
$S O_{3} + H_{2} O \to H_{2} S O_{4}$

Answer: As above.

Effects of acid rain and how to reduce it

On soil chemistry:

Leaches (washes out) nutrients such as calcium, magnesium and potassium, so soil becomes infertile.
Releases toxic aluminium and other metal ions from soil minerals, which damage roots.
Makes soil acidic, harming useful soil microorganisms; crops and forests suffer (leaves yellow, trees die back).

On water bodies:

Lakes and rivers become acidic; fish eggs fail to hatch, and fish and other aquatic life die.
Aluminium washed in from soil poisons fish gills.

On buildings and metals: marble and limestone (calcium carbonate) are eaten away:
$C a C O_{3} + H_{2} S O_{4} \to C a S O_{4} + H_{2} O + C O_{2}$
(marble monuments lose their shine, as with 'marble cancer'); iron and steel structures corrode faster.

Reduction:

Use low-sulphur fuels, or remove sulphur before burning.
Remove SO₂ from chimney gases (scrubbing with lime or limestone).
Fit catalytic converters in vehicles to convert NO into N₂; use public transport, CNG, electric vehicles.
Add lime to acidified lakes and soils to neutralise them (a short-term fix).

Worked example

Why does acid rain make a lake lifeless even far from any factory?

Try it first, then show the solutionSolution

SO₂ and NO₂ are carried long distances by wind before falling as acid rain.
The lake becomes acidic, and aluminium is washed in from surrounding soil.
Fish eggs do not hatch and fish die.

Answer: Pollutants travel; acidity and aluminium kill aquatic life.

Global warming and greenhouse gases

The Sun's short-wave radiation passes through the atmosphere and warms the Earth. The Earth gives off long-wave infrared (heat) radiation, part of which is absorbed and sent back by greenhouse gases. This greenhouse effect keeps the Earth warm enough for life. Increasing amounts of these gases trap more heat, raising the average temperature: global warming.

Gas	Main sources	Ways to reduce
Carbon dioxide	burning coal, petrol, diesel, wood; deforestation	use renewable energy (solar, wind, hydro); efficient vehicles; plant trees; stop deforestation
Methane	paddy fields, cattle (digestion), decaying waste in landfills, marshes, coal mines	capture biogas from waste and dung; better landfill management; composting
Oxides of nitrogen (e.g. N₂O)	nitrogen fertilisers, vehicle engines, burning fuels	use fertilisers carefully (only as needed); catalytic converters
Water vapour	evaporation from oceans; rises as the air warms	follows the temperature: controlling the other gases limits it

Effects: melting glaciers and polar ice, rising sea level (flooding low coasts), changed rainfall, more heatwaves, droughts and storms, loss of species, spread of diseases.

Worked example

Name two greenhouse gases released in rice-growing villages and one way to reduce each.

Try it first, then show the solutionSolution

Methane from waterlogged paddy fields and cattle: collect dung in biogas plants; better water management of fields.
Nitrous oxide from fertiliser: use fertiliser only as needed.

Answer: Methane and nitrous oxide, as above.

Ozone: formation, functions and depletion

Ozone (O₃) is an allotrope of oxygen with three atoms per molecule. Most of it is in the stratosphere (about 15-35 km up), forming the ozone layer.

Formation: high-energy ultraviolet (UV) radiation splits oxygen molecules into atoms, which then join with other oxygen molecules:
$O_{2} U V O + O$
$O + O_{2} \to O_{3}$
Overall: $3 O_{2} \to 2 O_{3}$

Functions: the ozone layer absorbs most of the harmful UV radiation from the Sun, acting as a protective shield. Without it, more UV would reach the ground, causing skin cancer, cataracts (eye damage), weakened immunity, damage to crops and to plankton at the base of ocean food chains.

Destruction (chemicals named only):

Chlorofluorocarbons (CFCs), e.g. freons, used in old refrigerators, air conditioners, aerosol sprays and foam-making.
Halons (in some fire extinguishers).
Carbon tetrachloride and methyl chloroform (solvents).
Nitric oxide (NO) from high-flying supersonic jets.

These release free radicals (e.g. chlorine atoms) high in the atmosphere that break down ozone. (The reactions are not in the syllabus.) CFCs are being phased out under international agreement.

Worked example

Write the equations for the formation of ozone in the upper atmosphere.

Try it first, then show the solutionSolution

$O_{2} U V O + O$
$O + O_{2} \to O_{3}$

Answer: As above.

Water: what is useful and what is harmful

Natural water is a solution: it contains dissolved gases, dissolved salts and sometimes suspended matter and microbes.

Beneficial:

Dissolved oxygen: fish and other aquatic animals breathe it through gills. Oxygen is more soluble in cold water.
Essential minerals: salts of calcium, magnesium, sodium, potassium; a little fluoride helps teeth; aquatic plants use dissolved carbon dioxide for photosynthesis.

Potentially harmful:

Toxic heavy metals: mercury, lead, cadmium, arsenic from industries, mining and batteries; they accumulate in living things and increase up the food chain.
Plastics: do not decompose; animals swallow them or get entangled; break into microplastics that enter food chains.
Sewage: organic waste is broken down by bacteria that use up dissolved oxygen, so fish suffocate; it also carries disease germs (cholera, typhoid, hepatitis A); nutrients from sewage and fertiliser cause algal bloom, which further cuts oxygen.
Pesticides (e.g. DDT) washed from farms: poison aquatic life and become concentrated up the food chain (biomagnification) in fish and birds.

Worked example

Why do fish die when untreated sewage is let into a pond?

Try it first, then show the solutionSolution

Bacteria decompose the organic matter in sewage.
They use up the dissolved oxygen in the water.
Fish cannot get enough oxygen and suffocate.

Answer: Dissolved oxygen is used up.

Minamata disease: mercury in water

Minamata disease is mercury poisoning first identified in the 1950s around Minamata Bay in Japan. A chemical factory discharged waste containing mercury compounds into the bay. Bacteria and the food chain turned and concentrated it as methylmercury in fish and shellfish, which local people ate.

Symptoms: damage to the nervous system: numbness of hands and feet, muscle weakness, poor coordination, damage to vision, hearing and speech; in severe cases paralysis and death. Babies of exposed mothers were born with defects.

Lesson: heavy metals are not removed by the body or broken down in nature; they build up along food chains. Industrial waste must be treated to remove heavy metals before discharge, and fish from polluted waters should not be eaten.

Worked example

Which metal causes Minamata disease, how did it reach people, and which body system does it attack?

Try it first, then show the solutionSolution

Mercury from factory waste.
It accumulated in fish and shellfish that people ate.
It damages the nervous system.

Answer: Mercury; through contaminated seafood; nervous system.

Chemistry in real life: Atmospheric and Environmental Chemistry

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Sulphur in coal

Suppose a power station burns 1 tonne (1000 kg) of coal containing 1.6% sulphur by mass, with no treatment of the chimney gases.

Find the mass of sulphur dioxide released and the mass of sulphuric acid it could form. (S = 32, O = 16, H = 1)

Try it first, then show the solutionSolution

Sulphur = 1.6% of 1000 kg = 16 kg.
$S + O_{2} \to S O_{2}$ : 32 kg S gives 64 kg SO₂, so 16 kg gives 32 kg SO₂.
Each S atom ends up in one H₂SO₄ (Mr 98): 32 kg S → 98 kg, so 16 kg → 49 kg H₂SO₄.

Answer: 32 kg of SO₂; up to 49 kg of sulphuric acid.

Memory hook: Follow the sulphur atom: its mass ratio is fixed by the formulae.

Fridge disposal

Suppose a family is throwing away a very old refrigerator, and the scrap dealer plans to break it open in the yard.

Explain why the coolant should be recovered by trained technicians.

Try it first, then show the solutionSolution

Old refrigerators may contain CFCs (freons) as coolant.
If released, CFCs rise to the stratosphere and destroy ozone.
Thinner ozone lets more UV reach the Earth, raising risks of skin cancer and cataracts.

Answer: To prevent CFCs escaping and depleting the ozone layer.

Memory hook: Old fridge, ozone risk.

Carbon dioxide from a car

Suppose a car burns fuel equivalent to 12 kg of carbon on a long trip.

Calculate the mass of carbon dioxide released and name the environmental problem it adds to. (C = 12, O = 16)

Try it first, then show the solutionSolution

$C + O_{2} \to C O_{2}$ : 12 kg C gives 44 kg CO₂.
Carbon dioxide is a greenhouse gas: it adds to global warming.

Answer: 44 kg of CO₂; global warming.

Memory hook: Every 12 of carbon becomes 44 of CO₂.

Topics in this chapter

Atmospheric and Environmental Chemistry formula sheet

Sulphur dioxide from fuel: $S + O_{2} \to S O_{2}$; Sulphur in coal and oil.
Sulphuric acid in rain: $2 S O_{2} + O_{2} \to 2 S O_{3}$; Then SO₃ + H₂O → H₂SO₄.
Nitric oxide in engines: $N_{2} + O_{2} \to 2 N O$; High temperature.
Nitric acid in rain: $4 N O_{2} + 2 H_{2} O + O_{2} \to 4 H N O_{3}$; After 2NO + O₂ → 2NO₂.
Acid rain on marble: $C a C O_{3} + H_{2} S O_{4} \to C a S O_{4} + H_{2} O + C O_{2}$; Corrodes monuments.
Formation of ozone: $O + O_{2} \to O_{3}$; After UV splits O₂.

Atmospheric and Environmental Chemistry: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

Formation of acid rain

Show, with a labelled flow diagram, how acid rain forms and where it falls.

Draw

A factory chimney and a car exhaust emitting SO₂ and NO.
Arrows upwards into a cloud, with SO₂ → SO₃ and NO → NO₂ written along them.
In the cloud: H₂SO₄ and HNO₃ formed with water.
Rain falling on a lake, trees and a building.

Label

SO₂ from burning fuel
NO from engines
oxidation in air
acid rain (H₂SO₄, HNO₃)
lake
forest
marble building

Watch out: Write one equation on each arrow.

Greenhouse effect

Draw a labelled diagram to explain the greenhouse effect.

Draw

The Sun on one side; short-wave rays passing through the atmosphere to the Earth.
Long-wave (infrared) rays leaving the Earth's surface.
A layer of greenhouse gases sending part of the infrared back down.

Label

solar radiation
Earth's surface
infrared (heat) radiation
greenhouse gases (CO₂, CH₄, N₂O, H₂O)
heat trapped

Watch out: Use straight arrows for incoming and wavy arrows for outgoing heat.

How the school exam asks Atmospheric and Environmental Chemistry

The question patterns to expect, and the method that works for each.

Question type	How it is asked	Method
Acid rain equations	Equations for SO₂ and NO from their sources to the acids; effect on marble.	Follow the chain: element → oxide → higher oxide → acid.
Effects and remedies	Effects of acid rain on soil, water bodies and buildings; suggest measures.	One effect + one reason; one practical measure each.
Greenhouse gases	Name four gases, one source each, one way to reduce each; explain the greenhouse effect.	Use the source-remedy table.
Ozone	Equations for formation; functions; name ozone-depleting chemicals.	Names only for destroyers; no destruction reactions.
Water pollution	Beneficial and harmful substances; Minamata disease; sewage and oxygen; plastics; pesticides.	Name the pollutant, source and effect.

Tricks to remember Atmospheric and Environmental Chemistry

Short memory aids. Say each one aloud once, then use it on a question the same day.

S-O-S for sulphur
Sulphur → SO₂ → SO₃ → Sulphuric acid.
Use it when: Acid rain chain.
Hot engines make NO
Nitrogen and Oxygen only marry when it's very hot: N₂ + O₂ → 2NO.
Use it when: Oxides of nitrogen.
Four greenhouse gases: 'Water Can Make Noise'
Water vapour, Carbon dioxide, Methane, Nitrogen oxides.
Use it when: The four syllabus gases.
Minamata = Mercury
Both start with M; both hit the nerves (Mind).
Use it when: Heavy-metal poisoning.

Atmospheric and Environmental Chemistry: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Example 1: Ozone-depleting chemical · 1 mark · MCQExam level

Which of these depletes the ozone layer?
(a) methane
(b) chlorofluorocarbons
(c) water vapour
(d) nitrogen

Try it first, then show the solutionSolution

CFCs release chlorine in the stratosphere that breaks down ozone.

Answer: (b)

Example 2: Nitric acid in rain · 3 marks · Short answerExam level

Write the equations for the formation of nitric acid in acid rain, starting from the gases of the air in a car engine.

Try it first, then show the solutionSolution

$N_{2} + O_{2} \to 2 N O$ (high temperature in the engine)
$2 N O + O_{2} \to 2 N O_{2}$
$4 N O_{2} + 2 H_{2} O + O_{2} \to 4 H N O_{3}$

Answer: As above.

Example 3: Acid rain on soil and water · 4 marks · Short answerHarder exam level

State two effects of acid rain on soil and two on water bodies.

Try it first, then show the solutionSolution

Soil: nutrients like calcium and magnesium are leached out; toxic aluminium is released and soil microbes are harmed.
Water: lakes become acidic and fish die; aluminium washed in poisons fish.

Answer: As above.

Example 4: Greenhouse effect · 1 mark · Assertion-reasonHarder exam level

Assertion (A): An increase in methane in the air adds to global warming.
Reason (R): Methane absorbs infrared radiation given off by the Earth.
(a) Both (A) and (R) are true, and (R) is the correct explanation for (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation for (A).
(c) (A) is true and (R) is false.
(d) (A) is false and (R) is true.

Try it first, then show the solutionSolution

Methane is a greenhouse gas: it absorbs and re-emits outgoing heat, warming the air.

Answer: (a)

Example 5: Ozone formation and role · 4 marks · Long answerHarder exam level

(a) Write the equations for the formation of ozone. (b) State its function in the upper atmosphere. (c) Name two chemicals responsible for its depletion.

Try it first, then show the solutionSolution

(a) $O_{2} \to O + O$ (UV); $O + O_{2} \to O_{3}$
(b) It absorbs harmful ultraviolet radiation from the Sun.
(c) Chlorofluorocarbons (freons); carbon tetrachloride (also halons, methyl chloroform, NO from supersonic jets).

Answer: As above.

Example 6: Sewage and oxygen · 3 marks · Short answerHarder exam level

Explain why discharging untreated sewage and fertiliser run-off into a lake leads to the death of fish, though neither is directly poisonous.

Try it first, then show the solutionSolution

Nutrients cause algal bloom; algae die and decay.
Bacteria decomposing sewage and dead algae use up dissolved oxygen.
Fish suffocate for lack of oxygen.

Answer: Dissolved oxygen is depleted.

Example 7: Marble monument · 3 marks · Short answerHOTS / competency

A marble statue in a city loses its shine and shows pits over a few years. (a) Write the equation for the action of sulphuric acid rain on marble. (b) Name the gas evolved. (c) Suggest two measures to protect the statue.

Try it first, then show the solutionSolution

(a) $C a C O_{3} + H_{2} S O_{4} \to C a S O_{4} + H_{2} O + C O_{2}$
(b) Carbon dioxide.
(c) Control SO₂ and NO emissions nearby (low-sulphur fuel, CNG, catalytic converters); restrict polluting traffic and industry around the monument.

Answer: As above.

Example 8: Biomagnification · 3 marks · Short answerHOTS / competency

Water in a lake has a very small concentration of mercury, yet fish-eating birds there have high mercury levels. Explain, and link it to Minamata disease.

Try it first, then show the solutionSolution

Mercury is not broken down or excreted easily; it accumulates in tissues.
Each level of the food chain eats many organisms from the level below, so the concentration rises (plankton → small fish → big fish → birds).
In Minamata, people ate fish with concentrated mercury and suffered nerve damage.

Answer: Accumulation up the food chain (biomagnification).

Case-study practice (Section B style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 5-mark question split into 2 + 1 + 2 marks.

A town by the lake

Suppose a town has a coal-fired power station, a battery factory that discharges waste into a lake, and many farms that spray pesticides. Townspeople report dead fish, yellowing pine trees on nearby hills and corroded iron gates.

(i) · 2 marks
Which source causes the yellowing trees and corroded gates? Write one equation for the acid formed.
Answer
Answer: The power station (SO₂ from sulphur in coal → acid rain): $S O_{3} + H_{2} O \to H_{2} S O_{4}$ .
(ii) · 1 mark
Name one heavy metal the battery factory may release and one disease linked to a heavy metal in water.
Answer
Answer: Lead, mercury or cadmium; Minamata disease (mercury).
(iii) · 2 marks
Give two reasons, from different sources, why fish in the lake are dying.
Answer
Answer: Acid rain makes the water acidic; heavy metals and pesticides poison fish (also oxygen loss if sewage is present).

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Name two greenhouse gases and one source of each. (2 marks) (2 marks)

Step	Marks
Carbon dioxide: burning fossil fuels	1
Methane: paddy fields / cattle / landfills	1

Write three equations showing how sulphur in fuel forms sulphuric acid in rain. (3 marks) (3 marks)

Step	Marks
$S + O_{2} \to S O_{2}$	1
$2 S O_{2} + O_{2} \to 2 S O_{3}$	1
$S O_{3} + H_{2} O \to H_{2} S O_{4}$	1

What is Minamata disease? Give its cause, how it reaches people and two symptoms. (4 marks) (4 marks)

Step	Marks
Poisoning by mercury (compounds)	1
From industrial waste discharged into water	1
Accumulates in fish and shellfish eaten by people	1
Two of: numbness, poor coordination, damage to vision/hearing/speech, paralysis, birth defects	1

Where students lose marks in Atmospheric and Environmental Chemistry

The slips examiners see most often, and what to write instead.

Mistake: Writing destruction reactions for ozone
The syllabus asks only for names of ozone-destroying chemicals; long reactions waste time and invite errors.
Wrong working
Writing chlorine radical chain reactions with CFCs.
Right working
Name the chemicals: CFCs (freons), halons, carbon tetrachloride, methyl chloroform, NO from supersonic jets.
Do this: Formation: equations. Destruction: names only.
Usually costs: Time, and marks if wrong.
Mistake: Confusing ozone depletion with global warming
Both involve gases in the air, so causes and effects are mixed.
Wrong working
Ozone depletion is caused by carbon dioxide and makes the Earth hotter.
Right working
Ozone depletion (CFCs) lets in more UV; global warming (CO₂, CH₄) traps more heat.
Do this: UV and shield for ozone; heat and blanket for greenhouse.
Usually costs: 1-2 marks.
Mistake: Unbalanced acid-rain equations
Students skip coefficients in the oxidation steps.
Wrong working
SO₂ + O₂ → SO₃
Right working
$2 S O_{2} + O_{2} \to 2 S O_{3}$
Do this: Count O atoms on each side.
Usually costs: 1 mark.
Mistake: Wrong source of oxides of nitrogen
Students think nitrogen oxides come from nitrogen in fuel.
Wrong working
NO comes from nitrogen present in petrol.
Right working
NO forms when nitrogen and oxygen of the air combine at the high temperatures in engines and furnaces.
Do this: Air + heat → NO.
Usually costs: 1 mark.
Mistake: Vague effects
Answers like 'harms the environment' earn nothing.
Wrong working
Acid rain is bad for soil.
Right working
Acid rain leaches calcium and magnesium from soil and releases toxic aluminium.
Do this: Name the specific chemical change.
Usually costs: 1 mark.

Practice questions on Atmospheric and Environmental Chemistry

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQExam level
Minamata disease is caused by:
(a) lead
(b) arsenic
(c) mercury
(d) cadmium
Hint
M and M.
Answer
(c)
Q2 · 1 mark · MCQExam level
The gas mainly responsible for acid rain from burning coal is:
(a) CO
(b) SO₂
(c) CH₄
(d) O₃
Hint
Sulphur in coal.
Answer
(b)
Q3 · 3 marks · Very short answerExam level
Name: (a) the layer of the atmosphere containing the ozone layer, (b) a greenhouse gas from paddy fields, (c) a pollutant that does not decompose and forms microparticles in water.
Hint
Strato-; methane; plastics.
Answer
(a) Stratosphere (b) Methane (c) Plastics
Q4 · 2 marks · Short answerExam level
Give two ways each of reducing (a) carbon dioxide and (b) methane in the atmosphere.
Hint
Energy and waste.
Answer
(a) Use solar/wind energy instead of fossil fuels; plant trees and stop deforestation. (b) Use dung and waste in biogas plants; manage landfills and compost waste.
Q5 · 2 marks · Short answerHarder exam level
Why are the oxides of nitrogen produced in a car engine but not when we simply breathe air at room temperature?
Hint
Temperature.
Answer
Nitrogen and oxygen combine only at very high temperatures, such as in the engine's combustion chamber. At room temperature they do not react. $N_{2} + O_{2} \to 2 N O$
Q6 · 3 marks · Short answerHarder exam level
Explain why fish may die in a lake in summer even without pollution, and why pollution by sewage makes it worse.
Hint
Gas solubility; decomposition.
Answer
Oxygen is less soluble in warm water, so summer water holds less dissolved oxygen. Sewage adds organic matter whose decomposition by bacteria uses up even more oxygen, so fish suffocate.
Q7 · 2 marks · Short answerExam level
State two functions of ozone in the atmosphere and two harmful effects on humans if the ozone layer thins.
Hint
UV.
Answer
Functions: absorbs harmful UV rays; protects living things and plankton. Effects: skin cancer; cataracts (also weaker immunity).
Q8 · 2 marks · Short answerHarder exam level
Explain how acid rain can make soil less fertile.
Hint
Leaching.
Answer
Acid dissolves and washes away (leaches) nutrients such as calcium, magnesium and potassium; it releases toxic aluminium ions and harms useful soil microbes.
Q9 · 2 marks · Short answerHarder exam level
How do catalytic converters and low-sulphur fuels each help reduce acid rain?
Hint
NO and SO₂.
Answer
Catalytic converters change nitrogen oxides in exhaust into harmless nitrogen. Low-sulphur fuels produce much less sulphur dioxide when burnt.
Q10 · 3 marks · Short answerHOTS / competency
Coal with 2% sulphur is burnt. What mass of sulphur dioxide is released per 500 kg of coal? (S = 32, O = 16)
Hint
Find S first.
Answer
S = 2% of 500 = 10 kg. 32 kg S → 64 kg SO₂, so 10 kg → 20 kg SO₂.
Q11 · 3 marks · Short answerHOTS / competency
A pesticide sprayed on fields is found in tiny amounts in a river, more in small fish, and much more in fish-eating birds whose eggshells become thin. (a) Name this effect. (b) Explain why it happens. (c) Suggest one measure.
Hint
Concentration rises up the chain.
Answer
(a) Biomagnification. (b) The pesticide is not broken down or excreted, so it builds up in each organism; predators eat many prey, concentrating it further. (c) Use fewer persistent pesticides; prefer biological pest control; keep buffer strips beside rivers.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.pH below which rain is called acid rain?Show answer
About 5.6.
2.Main acids in acid rain?Show answer
Sulphuric acid and nitric acid.
3.Where do oxides of nitrogen form?Show answer
At high temperatures in engines and furnaces (and lightning).
4.Four greenhouse gases in the syllabus?Show answer
Water vapour, carbon dioxide, methane, oxides of nitrogen.
5.What does ozone absorb?Show answer
Harmful ultraviolet radiation.
6.One ozone-depleting chemical?Show answer
Chlorofluorocarbons (freons).
7.Metal behind Minamata disease?Show answer
Mercury.
8.Why does sewage kill fish?Show answer
Its decomposition uses up dissolved oxygen.

Best order to study it

Learn the acid rain equations for sulphur and nitrogen.
Learn effects on soil, water bodies and buildings, and remedies.
Learn the greenhouse effect and the four gases with sources and remedies.
Learn ozone formation equations, functions and the named destroyers.
Learn beneficial and harmful substances in water, and Minamata disease.

Quick revision checklist

The night before the exam: can you do each of these without looking?

Can you write the full chain from S to H₂SO₄ and from N₂ to HNO₃?
Can you give two effects of acid rain each on soil and water bodies?
Can you give a source and a remedy for each greenhouse gas?
Can you write the ozone formation equations and name four depleting chemicals?
Can you explain Minamata disease in four points?
Can you explain how sewage, plastics and pesticides harm water life?

Atmospheric and Environmental Chemistry: frequently asked questions

Do I need the reactions of CFCs with ozone?

No. The 2028 syllabus says the chemicals responsible for destroying the ozone layer are to be named only, and their reactions are not required.

Is ozone good or bad?

High in the stratosphere it is protective, absorbing UV. Near the ground it is a pollutant in smog that irritates the lungs and eyes. The syllabus focuses on the protective ozone layer.

Is water vapour really a greenhouse gas?

Yes, it is the most abundant one. Its amount depends mainly on temperature, so it rises as other greenhouse gases warm the air and adds to the warming.

How is this chapter different from the Water chapter?

The Water chapter covers solutions, hardness, purification and water-borne diseases. This chapter covers pollution by chemicals: heavy metals, plastics, sewage and pesticides, and the useful dissolved oxygen and minerals.

Based on: CISCE ICSE 2028 Science (52) Chemistry (Science Paper 2) syllabus, Classes IX and X