Bronsted-Lowry acid
A species that donates a proton (H⁺) in a chemical reaction.
Acid-Base BasicsBronsted-Lowry base
A species that accepts a proton (H⁺) in a chemical reaction.
Acid-Base BasicsConjugate acid-base pair
Two species that differ by a single proton (H⁺); the conjugate base has one fewer H⁺ than its conjugate acid.
Acid-Base BasicsAutoionization of water
The reaction of water with itself to form H₃O⁺ and OH⁻, described by Kw = [H₃O⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25°C.
pH BasicspH / pOH
pH = −log[H₃O⁺]; pOH = −log[OH⁻]. At 25°C, pH + pOH = 14.
pH BasicsStrong acid / strong base
An acid or base that dissociates completely in water, allowing pH to be calculated directly from initial concentration.
Strong Acids/BasesWeak acid / weak base
An acid or base that only partially dissociates in water, requiring an equilibrium calculation (using Ka or Kb) to find pH.
Weak Acids/BasesAcid dissociation constant (Ka)
The equilibrium constant for a weak acid's dissociation reaction; a larger Ka means a stronger (more dissociated) weak acid.
Weak Acids/BasesBase dissociation constant (Kb)
The equilibrium constant for a weak base's reaction with water; a larger Kb means a stronger (more dissociated) weak base.
Weak Acids/BasesKa × Kb = Kw
The relationship between the Ka of an acid and the Kb of its conjugate base, both linked to the water autoionization constant Kw.
Weak Acids/BasesPercent ionization
The percentage of a weak acid or base that has dissociated at equilibrium, relative to its initial concentration.
Weak Acids/BasesNeutralization reaction
A reaction between an acid and a base that produces water and a salt, with protons transferring from the acid to the base.
Acid-Base ReactionsOxoacid
An acid containing oxygen, whose strength generally increases with the number of oxygen atoms (and therefore the electronegative pull) bonded to the central atom.
Molecular StructureTitration
A technique using a solution of known concentration (titrant) added to a solution of unknown concentration until the reaction is complete, used to determine the unknown concentration.
TitrationsEquivalence point
The point in a titration where moles of titrant added exactly equal the moles needed to completely react with the analyte.
TitrationsHalf-equivalence point
The point in a weak acid/base titration where exactly half of the original acid (or base) has been neutralized; at this point, pH = pKa (or pOH = pKb).
TitrationspKa
pKa = −log(Ka); a smaller pKa corresponds to a stronger acid.
pH & pKaBuffer
A solution containing a weak acid and its conjugate base (or a weak base and its conjugate acid) that resists changes in pH when small amounts of acid or base are added.
BuffersHenderson-Hasselbalch equation
pH = pKa + log([conjugate base]/[acid]) — used to calculate the pH of a buffer solution from the ratio of conjugate base to acid.
BuffersBuffer capacity
A measure of how much acid or base a buffer can neutralize before its pH changes significantly; maximized when the concentrations of the weak acid and conjugate base are roughly equal.
Buffers