10.1

Water

Cambridge IGCSE Chemistry (0620)  · Unit 10: Chemistry of the environment  · 13 flashcards

Water is topic 10.1 in the Cambridge IGCSE Chemistry (0620) syllabus , positioned in Unit 10 — Chemistry of the environment , alongside Air and air quality and Carbon dioxide and methane.

This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical).

The deck below contains 13 flashcards — 9 key concepts and 4 identification cards — covering the precise wording mark schemes reward.

What the Cambridge 0620 syllabus says

Official 2026-2028 spec

These are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.

  1. Describe Describe chemical tests for the presence of water using anhydrous cobalt(II) chloride and anhydrous copper(II) sulfate
  2. Describe Describe how to test for the purity of water using melting point and boiling point
  3. Explain Explain that distilled water is used in practical chemistry rather than tap water because it contains fewer chemical impurities
  4. State State that water from natural sources may contain substances, including: (a) dissolved oxygen (b) metal compounds (c) plastics (d) sewage (e) harmful microbes (f) nitrates from fertilisers (g) phosphates from fertilisers and detergents
  5. State State that some of these substances are beneficial, including: (a) dissolved oxygen for aquatic life (b) some metal compounds provide essential minerals for life
  6. State State that some of these substances are potentially harmful, including: (a) some metal compounds are toxic (b) some plastics harm aquatic life (c) sewage contains harmful microbes which cause disease (d) nitrates and phosphates lead to deoxygenation of water and damage to aquatic life
  7. Describe Describe the treatment of the domestic water supply in terms of: (a) sedimentation and filtration to remove solids (b) use of carbon to remove tastes and odours (c) chlorination to kill microbes
Key Concept Flip

What chemical is used to test for the presence of water?

Answer Flip

Anhydrous cobalt(II) chloride or anhydrous copper(II) sulfate are used. Anhydrous means the chemical has no water molecules. Remember to specify anhydrous.

Key Concept Flip

What is the colour change observed when using anhydrous cobalt(II) chloride to test for water?

Answer Flip

Anhydrous cobalt(II) chloride changes from blue to pink in the presence of water. Cobalt chloride paper can also be used which also turns from blue to pink.

Key Concept Flip

What is the colour change observed when using anhydrous copper(II) sulfate to test for water?

Answer Flip

Anhydrous copper(II) sulfate changes from white to blue in the presence of water.

Key Concept Flip

How can the purity of water be tested?

Answer Flip

By measuring its melting point and boiling point. Pure water boils at exactly 100°C and melts at exactly 0°C. Any impurities will change these values.

Key Concept Flip

Why is distilled water used in practical chemistry?

Answer Flip

Distilled water contains fewer chemical impurities than tap water. These impurities can interfere with experiments and give inaccurate results.

Key Concept Flip

Name three substances that may be found in water from natural sources.

Answer Flip

Dissolved oxygen, metal compounds, plastics, sewage, harmful microbes, nitrates from fertilizers, phosphates from fertilizers and detergents are all possibilities. Any three are acceptable.

Key Concept Flip

Give one reason dissolved oxygen is beneficial in natural water sources.

Answer Flip

Dissolved oxygen is essential for aquatic life (fish, plants, etc.) to survive.

Key Concept Flip

Give one reason metal compounds are beneficial in natural water sources.

Answer Flip

Some metal compounds provide essential minerals necessary for life.

Example: iron is needed for healthy blood.
Key Concept Flip

Give an example of a potentially harmful substance found in natural water sources.

Answer Flip

Some metal compounds are toxic. Sewage contains harmful microbes which cause disease. Plastics can harm aquatic life. Nitrates and phosphates lead to deoxygenation of water, harming aquatic life.

Key Concept Flip

Outline the process of sedimentation in water treatment.

Answer Flip

Sedimentation involves allowing solid particles to settle to the bottom of the water due to gravity. This removes larger insoluble impurities.

Key Concept Flip

Outline the process of filtration in water treatment.

Answer Flip

Filtration involves passing the water through a filter (

Example: sand) to remove any remaining solid particles that did not settle during sedimentation.
Key Concept Flip

What is the purpose of using carbon in water treatment?

Answer Flip

Carbon is used to remove tastes and odours from the water. It absorbs the chemicals causing these problems.

Key Concept Flip

What is the purpose of chlorination in water treatment?

Answer Flip

Chlorination involves adding chlorine to the water to kill any remaining microbes (bacteria, viruses) and make the water safe to drink.

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9.5 Corrosion 10.2 Air and air quality

Tips to avoid common mistakes in Water

More topics in Unit 10 — Chemistry of the environment

Water sits alongside these Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

10.2 Air and air quality

10 flashcards
10.3 Carbon dioxide and methane

13 flashcards

Cambridge syllabus keywords to use in your answers

These are the official Cambridge 0620 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.

water potable water drinking water purification filtration chlorination distillation desalination sewage treatment hard water soft water temporary hardness permanent hardness limescale ion exchange

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How to study this Water deck

Start in Study Mode, attempt each card before flipping, then rate Hard, Okay or Easy. Cards you rate Hard come back within a day; cards you rate Easy push out to weeks. Your progress is saved in your browser, so come back daily for 5–10 minute reviews until every card reads Mastered.