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pH and Solubility

The pH of a solution can change a salt's solubility. If the salt's anion is basic (it reacts with H⁺), then lowering the pH (adding acid) consumes that anion, and by Le Chatelier the dissolution equilibrium shifts to dissolve more solid. Salts whose anions do not react with H⁺ are largely unaffected by pH.

UNIT 8 TOPIC 8.11 • pH AND SOLUBILITY ACID-DRIVEN SOLUBILITY Lowering pH increases the solubility of a salt whose anion is basic. SOLUBILITY EQUILIBRIUM MA(s) M⁺ + A⁻ Ksp controls the point of saturation (a solid ⇌ its dissolved ions). MA(s) lattice dissolves M⁺ A⁻ cation basic anion ADD ACID H⁺ + A⁻ HA A⁻ is a weak-acid conjugate base — H⁺ pulls it out of solution as neutral HA. LE CHÂTELIER SHIFT Removing A⁻ makes Qsp < Ksp. So MA(s) ⇌ M⁺ + A⁻ shifts to the RIGHT — more solid dissolves to restore equilibrium. Solubility INCREASES as pH DECREASES. CED ANCHOR Only salts with a basic anion (F⁻, CO₃²⁻, PO₄³⁻, OH⁻, C₂O₄²⁻ …) become more soluble in acid. Salts of strong-acid anions (Cl⁻, NO₃⁻, ClO₄⁻) are pH-independent — those anions are not basic, so H⁺ can't remove them. AP Chemistry · Unit 8 · Acids and Bases
pH can drive solubility. If a salt's anion is basic (reacts with H⁺), lowering the pH consumes that anion, shifting the dissolution equilibrium to dissolve more solid. Salts of pH-neutral anions are largely unaffected by pH.
pH-Driven Solubility · Open the sandbox →

The trap mismodels the pH effect on solubility — for instance, expecting acid to always help, or missing that only salts with basic (H⁺-reactive) anions become more soluble in acid. Ask whether the anion reacts with H⁺; if so, added acid increases solubility.

The work

3 ways in · any order
Lesson
pH and Solubility

Lowering pH dissolves salts with basic anions by consuming the anion and shifting the equilibrium. The lesson reasons via Le Chatelier, then closes with a ten-scenario check.

Skill check · 10 scenarios
Diagnostic
10-item topic check

Ten items spanning the Topic 8.11 misconception: the pH effect on solubility mismodeled — which salts become more soluble in acid, and why.

Not started · 10 items · ~15 min
Targeted Practice
Drill a single misconception

Pick one of the failure modes you missed and drill it on its own. The round is adaptive: two correct in a row clears the misconception and moves you to the next.

Take the diagnostic to identify your misconceptions