Lesson-specific original diagram for Solubility equilibrium and hard-water unit mastery. Model: K sp ,Q sp ,s, common ion. It supports this lesson focus: Integrate Ksp, solubility, precipitation thresholds, qualitative analysis, and environmental interpretation without conflating Ksp with solubility itself. Text-only equivalent: use the model statement, identify variables/species, then connect the representation to the lesson calculation and evidence check.