Chemistry - Acids and Alkalis - offline version

Objectives:

• All students will understand how to test Acid strength using Indicators



• Most students will know the difference in behaviour of Acids and Alkalis



• Some students will understand the difference between Acids and Alkalis

National Curriculum:

Resources required:

• Various acids and alkalis, Universal indicator paper / solution. Test tubes, gas collecting tubes, Hydrochloric acid, Sodium Hydroxide, Calcium Carbonate, lime water

Teaching Activities:

Introduction

Activities

1. Outline Acids and Alkalis. Show how they can be tested and determined using indicators. Ensure students know pH numbers and colours for varying acid and alkali strengths, and neutral. Students should draw and label a Universal Indicator pH scale. Outline basic characteristics e.g. Acids are sour tasting; Alkalis are often soapy.



2. Describe acids as a solution of Hydrogen ions. They might form part of a solid molecule, but when dissolved in water the molecules split to create separate H+s. A strong acid has more free H+s in it. Recall the reaction of metals with Acids, and write word equations. Describe Alkalis as a solution of a Metal ‘base' (Hydroxide, Oxide or Carbonate). Give students an example of how Alkalis react with Acids. Again give word equations.Students should be given Dilute Hydrochloric acid, and a solution of Sodium Hydroxide. Using Universal Indicator to establish the pH of each, they should then add the acid by drops to the Sodium Hydroxide to see how the pH changes. Highlight that a specific amount of acid neutralises a specific amount of the metal base. Repeat using Calcium Carbonate (and test the gas given off).Use printable worksheet to reinforce formation of Salts during these reactions.

Summary

• Drop some acid on different stones e.g. limestone, sandstone, marble and observe the effect. Test pH of rainwater. Describe dissolved CO2 as the cause of the acidity. Ask them to predict the effect rain might have on limestone buildings etc. What do they think will happen as rainwater becomes slightly more acidic due to pollution. Discuss different methods for preventing acidification of soil and lakes.

Suggested homework:

• Ask students to research and write word equations for different neutralisation reactions used in every day life.