Read this to the class:
A school caretaker found two unlabelled spray bottles of clear liquid in a storage room. One is probably vinegar, which is used for cleaning windows. The other might be baking soda water, used for scrubbing. They look and smell almost the same, and nobody wants to guess. You can't taste chemicals to find out. Your team's job: build a colour-changing detector from red cabbage and use it to identify the mystery liquids.
Teams of three, with three jobs that rotate after every three liquids: Chemist (adds the drops), Colour checker (compares colours against white paper), Recorder (writes and colours in the results).
In the full lesson PDF
- Bet (5–10 min)
- Hunt (20 min)
- Reveal (10–15 min)
- Act (10 min)
- Background for the teacher
- Assessment
- Student sheet
US Letter, prints cleanly in black and white. The student sheet is on its own page, ready to photocopy.