Materials

• 10 ml gelatin
• 500 ml hot water
• baking soda
• oil of peppermint
• chlorophyll drops
• oil of licorice, fennel or anise
• food colouring
• small container with lid
• spoon

Instructions

1. Mix 10 ml of gelatin with 500 ml of hot water in a small bowl and stir until the gelatin is dissolved. Then let the mixture stand for 15 minutes.

2. Add enough baking soda to give the gelatin an abrasive feel and pasty texture.

3. Mix your toothpaste, testing different amounts of some or all of the remaining ingredients: chlorophyll drops, oil of peppermint, oil of licorice, and food colouring. This testing is what chemical engineers must do to create new health-care products.

(Source: Gear Up for Fun - The Association for the Promotion and Advancement of Science Education)