Acid base chemistry lesson for grades 2-3. Hands-on STEM investigation using cabbage juice as a pH indicator. Students encode secret messages with chemical reactions. Dollar-store materials. THE COLOR CODE CHALLENGE A Single-Lesson Edition from The Cipher Lab — Velvet Rigor EDU Where Chemistry Meets Mystery and Logic Saves the Day The famous cabbage juice pH indicator demo — finally taught with rigor. Students mix cabbage juice with household acids and bases (vinegar, lemon juice, baking soda