In this challenge, learners figure out how to make a juice stain disappear. (Younger learners will definitely need assistance, and safety instructions are included in the PDF.) First they experiment with cleaning solutions (vinegar, dishwasher detergent, and bleach) and types of juice (beet, purple grape, and cranberry). The experimental surface is a laminated paper grid (grid design in PDF) on which they drop solutions. A cloth used to blot up juice from the grid becomes the surface for learners to test which solution they think will best make stains disappear. Some background information is provided about how some cleaners work by adding and removing hydrogen atoms (acid and base reactions, e.g. vinegar and dishwasher detergent), and others work by removing and adding electrons (oxidation-reduction reactions, e.g. bleach).