IMAT Chemistry Practice Exam 2026 – Your All-in-One Guide to Exam Success!

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For a weak acid HA, which constant describes its acid strength?

Acid strength is quantified by the acid dissociation constant for HA. For the equilibrium HA ⇌ H+ + A−, Ka = [H+][A−]/[HA]. A larger Ka means more HA dissociates in water, so the acid is stronger; a smaller Ka means less dissociation, so it is weaker. The related concept, pKa = −log Ka, shows that smaller pKa corresponds to stronger acid.

The other constants don’t describe acid strength: Kb is the base dissociation constant for the conjugate base, Kw is the autoionization constant of water, and Ksp is the solubility product for sparingly soluble salts.

Ksp