Atmospheric and Environmental Chemistry
ICSE Class 9 · Chemistry · Chapter 8
What this chapter covers
- Atmospheric pollution
- Acid rain
- Global warming
- Ozone depletion
- Water pollution
Key points
- Atmospheric pollution is the presence of harmful substances in air, mostly from burning coal, petroleum, crop stubble and garbage.
- Acid rain has a pH below about 5.6 and contains sulphuric, sulphurous, nitric and carbonic acids.
- Sulphur in fuels gives SO2 and SO3, which form H2SO3 and H2SO4; high temperatures in furnaces and engines give NO and NO2, which form HNO3.
- Acid rain leaches nutrients and releases toxic aluminium in soil, acidifies lakes and kills fish, and corrodes marble and metals.
- Greenhouse gases (water vapour, carbon dioxide, methane, oxides of nitrogen) absorb infrared radiation from the Earth; their increase causes global warming.
- Greenhouse gases are reduced by cleaner energy, saving fuel, protecting forests, using biogas and using fertilisers carefully.
- Ozone forms in the stratosphere by O2 → O + O and O + O2 → O3, and absorbs harmful ultraviolet radiation.
- CFCs, halons, carbon tetrachloride and oxides of nitrogen destroy ozone; the Montreal Protocol phased out CFCs.
- Natural water carries beneficial dissolved oxygen and essential minerals; it is polluted by toxic heavy metals (Minamata disease from mercury), plastics, sewage and pesticides.
Questions answered
Define a pollutant and name three major air pollutants.
A pollutant is a substance that, in excess, harms living things or their surroundings. Sulphur dioxide, oxides of nitrogen and carbon monoxide.
Why is ordinary rain slightly acidic, and when is rain called acid rain?
Ordinary rain dissolves carbon dioxide and forms weak carbonic acid, giving a pH of about 5.6. Rain is called acid rain when its pH is below about 5.6 because of dissolved acids of sulphur and nitrogen.
Write equations to show how oxides of nitrogen are formed in a car engine and how they form nitric acid.
N2 + O2 → 2NO; 2NO + O2 → 2NO2; 4NO2 + 2H2O + O2 → 4HNO3.
State two effects of acid rain on soil.
It leaches nutrients such as calcium and potassium out of the soil, and it releases toxic aluminium that harms plant roots.
Why does acid rain damage marble buildings? Write the equation.
Marble is calcium carbonate, which reacts with sulphuric acid. CaCO3 + H2SO4 → CaSO4 + H2O + CO2.
What is the greenhouse effect? Why is the natural greenhouse effect useful?
The greenhouse effect is the warming of the Earth by gases that absorb infrared radiation from its surface. Without it the Earth's average temperature would be about –18 °C.
Name four greenhouse gases and one source of each.
Water vapour (evaporation), carbon dioxide (burning fuels), methane (rice fields, cattle, landfills), nitrous oxide (nitrogen fertilisers).
Suggest three ways of reducing the amount of carbon dioxide released into the atmosphere.
Using solar and wind power instead of coal; using public transport; planting and protecting forests.
Past board exam questions
ICSE 2019 sample paper · 1 mark
The gas that causes the greenhouse effect:
- Oxygen
- Ammonia
- Methane
- Hydrogen Sulphide
Show answer
Methane