Lesson-specific original diagram for Buffer systems and equilibrium response. Model: K a= [H 3O +][A -] [HA]. It supports this lesson focus: A buffer contains a weak acid/base and its conjugate partner; added acid/base is consumed stoichiometrically before equilibrium re-establishes. Text-only equivalent: use the model statement, identify variables/species, then connect the representation to the lesson calculation and evidence check.