Teach-Primary-Issue-19.3

• What is the difference between a reversible and an irreversible chemical change? • Which techniques can you use to sperate mixtures? • Which kitchen ingredients are soluble and insoluble? • How can you make a soluble substance dissolve? bake a cake, however, would be an irreversible change, because the mixture cannot be separated back into its constituent parts. Provide the equipment in Fig. 1 and set up a carousel of activities. Allow the pupils to experiment and attempt to combine and separate the ingredients 2 | MIXING AND SEPARATING Explain that the action of mixing can be reversible, depending on what you’re combining. For example, mixing different fruits to make a fruit salad is reversible, because the fruits could be separated by hand. Combining ingredients to • Experiment with ice cubes and the time they take to melt. What could make them melt faster or more slowly? • Make jelly! Let the class experience jelly cubes dissolving in water and then setting in a jelly mould – and then enjoy eating it! EXTENDING THE LESSON using the various resources. Discuss the children’s findings and experiences, and address any misconceptions. 3 | DISSOLVING When a substance dissolves in liquid, it is called a solution . In groups of two, ask the pupils to think about examples in the kitchen where they may dissolve foods, and then share their ideas with the class. Examples might include coffee granules, sugar, and a stock cube. Do the pupils think that all materials will dissolve in water? Working as a class, experiment using eight cups of warm water and eight materials (e.g. sugar, sugar cubes, salt, rice, sand, coffee, gravy granules and flour). Before mixing each substance with the water, ask the pupils what they think will happen. Will the material be soluble and dissolve, or will it be insoluble and not dissolve? Afterwards, discuss whether all the soluble materials dissolved at the same speed. Which materials dissolved quickest or slowest? Did stirring the solution alter anything? What would changing the temperature of the water do? Was there a difference between the sugar cubes and the pouring sugar? Hannah Shaw was a primary school teacher before working as the consultant teacher for Purely Nutrition and the PhunkyFoods programme. “There are many interesting experiments using food and simple equipment that you can complete safely at school, so dig in, and you might even end up with a semi-edible snack...” USEFUL QUESTIONS Ingredients Technique Resources Rice and flour Mixing Bowl and spoon Rice and flour combined Separating Bowl and sieve Salt and warm water Dissolving Cup and spoon Ice cubes Melting Plate Sand and water (‘dirty water’) Filtering Cup, funnel, filter paper and jug Fig 1. DOWNLOAD RESOURCES AT Download your FREE accompanying worksheets at tinyurl.com/tp-changes www.teachwire.net | 77