Science at key stage 3 (Year 9)
Unit 9E: Reactions of metals and metal compounds
Section 6: a. What is a salt?
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Objectives |
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- that when an alkali is added to an acid, neutralisation takes place
- how to obtain a neutral solution from an acid and an alkali
- the hazards associated with alkalis
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Activities |
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Outcomes |
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Children: |
- Remind pupils of work they did earlier on acids and alkalis and establish by quick questioning what they recall. If necessary, demonstrate the use of universal indicator to determine the acidity or alkalinity of a solution. Ask pupils about neutralisation and establish that a neutral solution is one with pH7 and that neutralisation is a chemical reaction. Remind pupils about everyday examples of neutralisation. Explain to pupils that they are going to neutralise hydrochloric acid with potassium hydroxide or sodium hydroxide and to find out exactly how much to add. Ask them to suggest how they could do this and adopt an appropriate technique. Point out the risks of using alkalis.
- Help pupils to carry out or demonstrate the reaction. Establish that potassium chloride or sodium chloride is formed, that sodium chloride is common salt and is an example of the class of compounds called 'salts'. Ask pupils to complete word equations for other neutralisation reactions.
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- identify that a solution of pH7 is neutral
- explain the safety precautions that need to be taken when using alkalis
- use the technique adopted to obtain a neutral solution from which sodium chloride can be isolated
- represent reactions by word equations
- identify the pattern in word equations and produce a general equation,
eg acid
+
alkali > salt +
water
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Points to note |
- Pupils will have used universal indicator and pH as a measure of acidity in unit 7E 'Acids and alkalis'.
- If a class information folder was built up during unit 7E 'Acids and alkalis', this could be referred to. Pupils could be asked to try to find other everyday examples of neutralisation.
- This activity provides an opportunity to use a pH probe and/or to introduce pupils to the use of a burette. A computer simulation might also be useful.
- Pupils are often confused by the uses of the word 'salt'. Teachers may therefore prefer to make potassium chloride and discuss this as an example of a salt that is not common salt. Pupils need practice in distinguishing salts from other types of compound.
- Extension: this activity offers further opportunities for some pupils to practise writing formulae and symbol equations.
Safety
- 0.1 mol dm-3 solutions of acid and alkali are suitable for this activity. At this concentration sodium hydroxide and potassium hydroxide are irritant. Mouth pipettes should not be used
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This unit is divided into sections. Each section contains a sequence of
activities with related objectives and outcomes. You can view this unit by
moving through the sections or print/download the whole unit.
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