Goals for the session

By the end, children aged 7 to 12 should be able to say that some substances are acids and some are alkalis, use a colour to sort them, and make a prediction before each test.

They should also practise the routines of a careful scientist: small amounts, labelled cups, one change at a time and a written result.

Children take away a completed colour chart and the idea that a colour change can reveal something hidden. With an adult at home, they can make a small batch of indicator again and test safe liquids from the kitchen.

Sample session: colour-changing cabbage (60 minutes)

Before the session, chop half a red cabbage, cover it with hot water, leave it for 20 minutes and strain it. The purple liquid is the indicator. For 12 children in groups of three you need: clear plastic cups, pipettes or teaspoons, and small labelled pots of lemon juice, white vinegar, bicarbonate of soda dissolved in water, washing soda solution made up by the adult, tap water and milk.

• 0-10 min: Show the purple liquid. Add a little lemon juice to one cup in front of the group and let them describe what they see.

• 10-15 min: Groups predict the colour for each test liquid and write it on a table.

• 15-40 min: Groups add a few drops of each liquid to a separate cup of indicator and record the actual colour.

• 40-50 min: Arrange the cups in a line from pinkest to greenest. Explain that pink shows acids and green shows alkalis.

• 50-60 min: Mix an acid cup and an alkali cup slowly and watch the colour move back towards purple. Discuss what happened.

Safety notes

Children wear safety glasses or goggles throughout. Washing soda irritates skin and eyes, so the adult prepares and pours it, and it is kept out of reach of younger children. Nothing is tasted, even familiar foods, because the cups have been used for testing. Have paper towels and a bowl of clean water ready, and wash hands at the end.

Adapting for different ages

Younger children can skip the prediction table and simply sort cups into two trays, pink side and green side. Older children can test extra household items brought from home, after the adult has checked them, and place them on the colour line. They can also write a short method so another group could repeat the test.

Key points

• Use a visible colour change to make an abstract idea concrete.

• Ask for a prediction before every test.

• Keep amounts small and let the adult handle anything irritant.

• End with a line of results children can see and explain.

Ready-made resources

Printable session plans and materials for this topic are available from EduTrend Contents: W4C-120 Young Scientists Lab.

Photos: Vitaly Gariev, Ryan Zazueta / Unsplash