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This chemistry extension module of the Salters' Science course revises and extends students’ ideas about the structure and properties of water. It deals with hardness of water, the action of soap and other detergents and properties of emulsions.

Processes associated with domestic water supply and waste water treatment are covered. Electrolysis of water and reactions of water with metals are demonstrated. Solubility in water (and other solvents) is tested and the presence of water of crystallisation in some crystalline salts is investigated.

Hardness in water is tested using soap. Students make their own sample of soap. Various methods of softening water are explored. Properties of emulsions are studied, with practical activities on toothpaste and shampoos. Suggestions for investigative work are given.

Lesson 1: What do we know about water?
Students’ existing ideas about water are explored. Ideas about particles and changes of state are related to the water cycle.

Lesson 2: Fit to drink
Text exercises are used to introduce the processes used in water purification and sewage treatment.

Lesson 3: Properties of water
Practical experiments on the reaction of water with metals, water as a solvent, and salt hydrates.

Lesson 4: Healthy water
Properties of chlorine are demonstrated. A word puzzle is used to introduce chemical contributions to public health and hygiene.

Lesson 5: What causes hard water?
Experiments show that some types of rock dissolve slightly in water. The effect of dissolved salts on soap is tested.

Lesson 6: Soap
Students make soap. The actions of soap and soapless detergents are compared.

Lesson 7: Softening water
Different methods of softening water are tested. The use of ion exchange resins to exchange both cations and anions is demonstrated.

Lesson 8: All shook up
The idea of dispersion is introduced and students make samples of cosmetic emulsions. Extension work on toothpaste is offered.

Lessons 9/10: Investigations
Outline suggestions are given for a number of investigations.

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