Water And Water Pollution

Learn it by playing

Answer these questions to earn energy, then fish and explore. No account needed.

For teachers: ready-to-use lesson slides, revision notes, diagrams for Water And Water Pollution (Co-ordinated Sciences (Double Award) [CIE], Chemistry) — use them in your lesson, or run the topic as a live class game.

Notes

Chemical Tests for Water

**Anhydrous cobalt(II) chloride** (blue) turns **pink** in the presence of water, forming hydrated cobalt(II) chloride.
**Anhydrous copper(II) sulfate** (white) turns **blue** in the presence of water, forming hydrated copper(II) sulfate.
Cobalt chloride paper is commonly used to test for water: blue → pink.
These tests are reversible: heating the hydrated salt drives off water, restoring the anhydrous colour.

Purity of Water

Pure water has a sharp **boiling point of 100 °C** and **melting point of 0 °C**.
Impurities **raise the boiling point** and **lower the melting point** of water.
Boiling/melting point data can be used to assess water purity.
**Distilled water** is produced by boiling water and condensing the steam, removing most dissolved impurities.
Distilled water is used in experiments to avoid interference from dissolved ions.

Water Treatment: Sedimentation and Filtration

Untreated water contains **insoluble impurities** (soil, plant matter) and **soluble impurities** (dissolved calcium, metal compounds).
First, water is left to stand in sedimentation tanks so that heavy particles settle by gravity.
The water is then **filtered through sand and gravel** to remove smaller suspended particles.

Water Treatment: Carbon Filtration and Chlorination

**Filtration through carbon (charcoal)** removes unpleasant tastes and odours.
**Chlorination** kills bacteria and other microorganisms that are too small to be filtered.
Chlorine is carefully added to the water supply to prevent diseases such as **cholera** and **typhoid**.

Summary of Water Treatment Stages

Stage 1: **Sedimentation** – solids settle out.
Stage 2: **Filtration** through sand/gravel – removes smaller particles.
Stage 3: **Carbon filtration** – removes tastes and odours.
Stage 4: **Chlorination** – kills microbes.

Benedict's test for reducing sugars: colour change from blue to green/yellow/orange/red indicates increasing glucose concentration.

Practice questions

Free preview — 8 of 12 questions. Sign up to see them all.

1.Which of the following is the colour change observed when anhydrous cobalt(II) chloride is added to water?
Easy
- Ablue to pink
- Bpink to blue
- Cwhite to blue
- Dblue to white
2.What colour does anhydrous copper(II) sulfate turn in the presence of water?
Easy
- Awhite to blue
- Bblue to white
- Cwhite to pink
- Dpink to white
3.Pure water boils at exactly 100 °C and melts at exactly 0 °C.
Easy
True or false?
4.State one reason why distilled water is used in practical chemistry rather than tap water.
Medium
5.Complete the sentence about the test for water using anhydrous copper(II) sulfate.
Medium
Anhydrous copper(II) sulfate $is ____ and$ turns $____ in$ the presence of water.
6.Match each stage of water treatment with its purpose.
Medium
- Sedimentation
- Filtration through carbon
- Chlorination
- Removes unpleasant tastes and odours
- Kills bacteria and microorganisms
- Removes mud, sand and other particles
7.Place the following stages of water treatment in the correct order.
Medium
- Chlorination
- Sedimentation and filtration
- Filtration through carbon
8.Give the chemical equation for the reaction of anhydrous cobalt(II) chloride with water.
Hard

Slides

Chemical Tests for Water

Water can be detected using anhydrous cobalt(II) chloride or anhydrous copper(II) sulfate.
Anhydrous cobalt(II) chloride is blue; it turns pink when hydrated (CoCl₂·6H₂O).
Anhydrous copper(II) sulfate is white; it turns blue when hydrated (CuSO₄·5H₂O).

What colour change does anhydrous cobalt(II) chloride show when water is added?

White to blue
Blue to pink
Pink to blue
Blue to white

Purity of Water

Pure water boils at 100 °C and melts at 0 °C.
Impurities raise the boiling point and lower the melting point.
Distilled water is purified by boiling and condensing, removing dissolved impurities.

Pure water has a boiling point $of ____ ^{\circ}C$ and a melting point $of ____ ^{\circ}C$ .

Water Treatment Overview

Untreated water contains insoluble impurities (soil, plant matter) and soluble impurities (dissolved ions).
Water treatment involves three main stages: sedimentation/filtration, carbon filtration, and chlorination.

Which of these are true about water treatment?

Sedimentation removes large particles by gravity.
Carbon filtration removes bacteria.
Chlorination kills microorganisms.

Stage 1: Sedimentation and Filtration

Water is left to stand in sedimentation tanks; heavy particles sink to form sediment.
The water is then filtered through sand and gravel to remove smaller particles.

What is the purpose of sedimentation in water treatment?

To kill bacteria
To remove dissolved salts
To allow heavy particles to settle
To add chlorine

Stage 2: Carbon Filtration

Water is filtered through carbon (charcoal).
This removes unpleasant tastes and odours.

Filtration through carbon removes unpleasant $____ and ____$ .

Stage 3: Chlorination

Chlorine is added to kill bacteria and other microorganisms.
Untreated water can cause diseases like cholera and typhoid.

Why is chlorine added during water treatment?

To remove insoluble particles
To kill microorganisms
To remove tastes and odours
To lower the boiling point

Summary of Water Treatment

Sedimentation & filtration: removes solid particles.
Carbon filtration: removes tastes and odours.
Chlorination: kills microorganisms.

Which of these are correct about water treatment?

Sedimentation removes dissolved ions.
Carbon filtration removes tastes and odours.
Chlorination kills bacteria.

Flashcards

What is the chemical test for water using anhydrous cobalt(II) chloride?

Anhydrous cobalt(II) chloride (blue) turns pink in the presence of water, forming hydrated cobalt(II) chloride.

What is the chemical test for water using anhydrous copper(II) sulfate?

Anhydrous copper(II) sulfate (white) turns blue in the presence of water, forming hydrated copper(II) sulfate.

What colour is anhydrous cobalt(II) chloride?

Blue.

What colour is hydrated cobalt(II) chloride?

Pink.

What colour is anhydrous copper(II) sulfate?

White.

What colour is hydrated copper(II) sulfate?

Blue.

How can the purity of water be tested?

By measuring its boiling point or melting point. Pure water boils at 100°C and melts at 0°C; impurities raise the boiling point and lower the melting point.

Why is distilled water used in practical chemistry instead of tap water?

Distilled water contains fewer chemical impurities that could interfere with chemical reactions and affect results.

How is distilled water produced?

By heating water to form vapour and then condensing it back to a liquid, removing most dissolved impurities.

What are the three main stages of water treatment?

1) Sedimentation and filtration to remove solids, 2) Filtration through carbon to remove tastes and odours, 3) Chlorination to kill microbes.

What is the purpose of sedimentation in water treatment?

To allow mud, sand and other particles to settle to the bottom by gravity, forming a layer of sediment.

What is the purpose of filtration through carbon in water treatment?

To remove unpleasant tastes and odours from the water.

What is the purpose of chlorination in water treatment?

To kill bacteria and other microorganisms that are too small to be trapped by filters.

Name two bacterial diseases that can arise from consuming untreated water.

Cholera and typhoid.

What are insoluble impurities in untreated water?

Soil, pieces of plants and other organic matter.

What are soluble impurities in untreated water?

Dissolved calcium, metallic compounds and inorganic pollutants.

What is the colour change when anhydrous cobalt(II) chloride is added to water?

Blue to pink.

What is the colour change when anhydrous copper(II) sulfate is added to water?

White to blue.

What is the boiling point of pure water?

100°C.

What is the melting point of pure water?

0°C.

How do impurities affect the boiling point of water?

Impurities increase the boiling point, so impure water boils above 100°C.

How do impurities affect the melting point of water?

Impurities decrease the melting point, so impure water melts below 0°C.

Unlock all 12 questions, slides, flashcards & more

Create a free account to see every question, the slides, flashcards and revision notes for this topic.

Past papers

Past-paper practice for this topic is coming soon.

🗂️ Coming soon