Acid strength

Acid strength is an acid’s tendency to donate a proton in a specified solvent or chemical environment. It is commonly quantified by an equilibrium constant or its logarithmic form, pKa.

Acid dissociation constant: The equilibrium constant for an acid transferring a proton to a base, usually water or solvent. It quantifies proton donation directly through the equilibrium between an acid and its conjugate base.
Brønsted–Lowry acid–base theory: A theory defining acids as proton donors and bases as proton acceptors. Acid strength compares how readily different Brønsted–Lowry acids donate protons.
Acid–base titration: A quantitative method that determines an acid or base concentration by reacting it with a measured standard solution. The titration curve and equivalence-point behavior depend on the acid’s dissociation strength.
pH: The negative base-ten logarithm of hydrogen-ion activity in a solution. pH describes a solution’s acidity, whereas acid strength describes a particular acid’s proton-donation tendency.
pKa: The negative base-ten logarithm of an acid dissociation constant. It expresses acid strength on a convenient scale: lower pKa generally means stronger acid in the same solvent.
Conjugate acid–base pair: Two species related by the gain or loss of one proton. An acid’s proton donation produces its conjugate base, whose stability influences the equilibrium.
Buffer solution: A solution that resists pH change through a weak acid–conjugate base pair or weak base–conjugate acid pair. A buffer is most effective near the pKa of its acid component.
Lewis acid: A species that accepts an electron pair to form a covalent bond. Lewis acidity is defined by electron-pair acceptance, not proton donation.
Solvent leveling effect: The limitation by a solvent of apparent acid or base strength through its own proton-transfer reactions. Water makes strong acids appear similarly strong because they protonate water nearly completely.
Chemical equilibrium: A dynamic state in which forward and reverse reaction rates are equal. Acid dissociation is an equilibrium, so strength depends on the relative amounts of products and reactants.

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