Introduce students to the significance of pH indicators with this colorful 2-part activity that explores solubility, equilibrium, Le Châtelier's principle, and acid-base chemistry. In part 1, students investigate how changes in pH affect solubility and then extend the investigation to magnesium hydroxide's solubility equilibrium. In part 2, students design their own inquiry-based experiment to further explore solubility equilibrium. Materials are sufficient for 10 groups of students.