Acids and alkalis are commonly found in our homes and school laboratories. They can be identified using indicators. We may use the pH scale to describe the relative acidity and alkalinity of substances. When acids are mixed with alkalis, neutralisation occurs and gives salts and water. Acids and alkalis are corrosive. We should be aware of the potential hazards associated when using them. Besides, the acidic air pollutants resulted from human activities may lead to the formation of acid rain, and adversely affect the environment and living things.

 

Through performing different practical works, e.g. classifying substances into acids and alkalis, measuring the pH of substances and obtaining salts from neutralisation, students will practise some science process skills, like observing, classifying, presenting data in graphical presentation for effective communication. Through the study of neutralisation, students learn that salt and water is formed when acids are mixed with alkalis, and that the mass of reactants and products is conserved in the reaction. This will help students realise the unifying concept “change and constancy”.