# Chemistry of the Environment

> CIE IGCSE Chemistry · CIE IGCSE Chemistry (0620)
> Source: https://www.owlsprep.com/study/cie-0620-u10-overview/
> Weight: 8-10% of total assessment, appearing in both MCQ and structured theory questions

This unit explores the chemistry of essential natural resources (water and air), human impacts on environmental health, and evidence-based solutions to reduce pollution, a core applied chemistry theme for IGCSE assessments.

**Prerequisites:** [Basic atomic structure and bonding](https://www.owlsprep.com/study/cie-0620-u3-bonding/); [Chemical reactions and balanced equations](https://www.owlsprep.com/study/cie-0620-u4-chemical-reactions/)

## Learning objectives

- Explain how to test for the presence and purity of water, and describe industrial drinking water treatment processes
- Analyse the composition of clean air and common sources of air pollution, including their impacts on human health and global climate
- Evaluate both the agricultural benefits and environmental risks of using artificial nitrogen and phosphorus fertilisers
- Apply core chemical principles to explain key environmental processes including photosynthesis and the greenhouse effect

## Unit at a glance

The unit follows a logical flow from the chemistry of water (our most critical biological resource) to the chemistry of the atmosphere and agricultural systems. You will connect foundational chemical concepts to real-world challenges including drinking water access, air quality regulation, climate change mitigation, and sustainable food production.

Assessment questions for this unit often combine recall of key tests and processes with extended response items asking you to evaluate tradeoffs of environmental interventions, such as fertiliser use limits or carbon reduction policies.

Work through the following subtopics in order to build your knowledge sequentially:
- [Water](https://www.owlsprep.com/study/cie-0620-u10-water/) — Covers tests for water presence and purity, drinking water treatment methods, and causes and impacts of water pollution.
- [Air Quality, Climate and Fertilisers](https://www.owlsprep.com/study/cie-0620-u10-air-quality-climate-and-fertilisers/) — Explores atmospheric composition, air pollution sources, greenhouse gas effects, and the chemistry and impacts of agricultural fertilisers.

## Common pitfalls

- **Wrong:** Confusing tests for water presence with tests for pure water
  - Why it fails: Anhydrous copper(II) sulfate turns blue with any water sample, but only 100% pure water has a boiling point of exactly 100°C at 1 atm pressure
  - Correct: Use anhydrous copper(II) sulfate to confirm water is present, and boiling point measurement to confirm full purity
- **Wrong:** Assuming all fertiliser use is environmentally harmful
  - Why it fails: Nitrogen and phosphorus fertilisers are critical to feeding much of the global population, but excess nitrate/phosphate runoff causes deoxygenation of water and damage to aquatic life
  - Correct: Evaluate both the food security benefits and pollution risks of fertilisers, and reference targeted application methods as a mitigation strategy

## Cheatsheet

| Key Concept | Relevant Subtopic | Core Detail |
| --- | --- | --- |
| Test for water presence | Water | Anhydrous $CuSO_4$ (white) → Hydrated $CuSO_4·5H_2O$ (blue) |
| Test for pure water | Water | Boiling point = 100°C at standard atmospheric pressure |
| Clean dry air composition | Air Quality, Climate and Fertilisers | 78% $N_2$, 21% $O_2$, 0.04% $CO_2$, <1% noble gases |
| Primary greenhouse gases | Air Quality, Climate and Fertilisers | $CO_2$, $CH_4$, nitrous oxide, CFCs, water vapour |
| Fertiliser runoff impact | Water | Excess nitrate/phosphate runoff causes deoxygenation of water and harms aquatic life |

## What's next

Begin your study of this unit with the Water subtopic, where you will master the practical tests and treatment processes that are frequently tested in short answer exam questions. Once you have completed both subtopics in this unit and worked through their associated practice questions, you will progress to the next major syllabus theme: organic chemistry.

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