Paper 4 Environment Structured Practice
5 structured exam questions on chemistry of the environment for IGCSE Chemistry Paper 4. Covers water treatment, fertilisers, air pollution, greenhouse effect, and climate change. Total: 25 marks.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Five structured questions in the style of IGCSE Chemistry Paper 4, totalling 25 marks. Write your answers in full before checking the mark scheme.
Question 1 (5 marks)
Water from a river is treated before it is safe to drink.
(a) State what is meant by potable water. [1]
(b) Describe the stages involved in treating river water to make it safe to drink. [3]
(c) State why chlorine is added during water treatment. [1]
Mark scheme
(a) Water that is safe to drink / water that has been treated to remove harmful substances and microorganisms [1].
(b) Sedimentation: large insoluble particles settle out / chemicals are added to make fine particles clump together and settle [1]. Filtration: the water is passed through sand/gravel beds to remove remaining solid particles [1]. Sterilisation/chlorination: chlorine is added to kill bacteria and other microorganisms [1].
(c) To kill bacteria / microorganisms / pathogens to prevent the spread of waterborne diseases [1].
Total: 5 marks
Question 2 (5 marks)
Farmers use fertilisers to improve crop growth. The three essential elements in fertilisers are nitrogen, phosphorus, and potassium (N, P, K).
(a) Explain why plants need nitrogen. [1]
(b) Name one nitrogen-containing fertiliser and state the nitrogen compound it contains. [1]
(c) Describe the process of eutrophication that can result from excessive use of fertilisers. [3]
Mark scheme
(a) Plants need nitrogen to make proteins / for healthy growth / to produce amino acids [1].
(b) Ammonium nitrate (NH₄NO₃) [1]. Accept: ammonium sulfate, urea, potassium nitrate (with appropriate compound named).
(c) Excess fertiliser is washed / leached from fields into rivers and lakes by rain [1]. The high concentration of nutrients (nitrates/phosphates) causes rapid growth of algae on the surface (algal bloom), which blocks light to underwater plants [1]. When the algae and plants die, bacteria decompose them, using up the dissolved oxygen. Aquatic organisms such as fish die due to lack of oxygen [1].
Total: 5 marks
Question 3 (5 marks)
Acid rain is caused by pollutant gases released into the atmosphere.
(a) Name two gases that cause acid rain. State their sources. [2]
(b) Write the equation for the reaction of sulfur dioxide with water. [1]
(c) Describe two harmful effects of acid rain. [2]
Mark scheme
(a) Sulfur dioxide (SO₂) --- formed from burning fossil fuels containing sulfur impurities / volcanic emissions [1]. Nitrogen oxides (NOₓ) --- formed when nitrogen and oxygen from the air react at the high temperatures inside car engines / power stations [1].
(b) SO₂ + H₂O → H₂SO₃ (sulfurous acid) [1] Accept: SO₃ + H₂O → H₂SO₄
(c) Any two from: damages/corrodes limestone buildings and statues (made of CaCO₃) [1]; kills fish and other organisms in lakes and rivers by lowering the pH [1]; damages leaves of trees and plants / leaches minerals from soil [1]; corrodes iron and steel structures [1].
Total: 5 marks
Question 4 (5 marks)
The greenhouse effect is essential for life on Earth, but human activities have enhanced it.
(a) Name two greenhouse gases. [1]
(b) Describe how the greenhouse effect works. [2]
(c) State two consequences of the enhanced greenhouse effect. [2]
Mark scheme
(a) Any two from: carbon dioxide (CO₂), methane (CH₄), water vapour [1]. Both must be named for the mark.
(b) Short-wavelength radiation from the Sun passes through the atmosphere and warms the Earth’s surface [1]. The Earth re-emits longer-wavelength infrared radiation. Greenhouse gases absorb this infrared radiation and re-emit it in all directions, including back towards Earth, keeping the atmosphere warm [1].
(c) Any two from: global temperature rise / global warming [1]; melting of polar ice caps and glaciers, leading to sea level rise and flooding of coastal areas [1]; more extreme/unpredictable weather events [1]; changes to habitats and ecosystems / extinction of species [1].
Total: 5 marks
Question 5 (5 marks)
Carbon dioxide levels in the atmosphere have increased significantly over the past 200 years.
(a) State two human activities that have contributed to the increase in atmospheric carbon dioxide. [2]
(b) Define the term carbon footprint. [1]
(c) Describe two strategies that can reduce a country’s carbon footprint. [2]
Mark scheme
(a) Burning fossil fuels (coal, oil, natural gas) in power stations, vehicles, and industry [1]. Deforestation / clearing forests (which would otherwise absorb CO₂ by photosynthesis) [1].
(b) The total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service, or event / by an individual or organisation [1].
(c) Any two from: using renewable energy sources (solar, wind, hydroelectric) instead of fossil fuels [1]; improving energy efficiency in buildings and transport / using electric vehicles [1]; planting trees / reforestation to absorb CO₂ [1]; carbon capture and storage technology [1]; reducing energy consumption / using less electricity [1].
Total: 5 marks
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