Acid base equilibrium tug-of-war

Definition

Acids and bases pull on opposite sides of water’s ionization balance, and Kw forbids hydronium and hydroxide from being abundant at the same time. Adding one species drives the other down until the constant is restored.

Adding acid floods the water with protons that react with hydroxide, collapsing the hydroxide population and shifting pH acidic. Adding base supplies hydroxide that hunts down free hydrogen, plummeting the proton population and shifting pH basic. In both cases the product of the two concentrations must return to Kw, so acids and bases drag the equilibrium to a new resting place rather than changing the rule.

Related concepts

Neutralization · Strong acid dissociation · Strong base dissociation

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Part of The Blueprint of Water · 🧪 chemistry