Key Terms

acid ionization

reaction involving the transfer of a proton from an acid to water, yielding hydronium ions and the conjugate base of the acid

acid ionization constant (K_a)

equilibrium constant for the ionization of a weak acid

acid-base indicator

organic acid or base whose color changes depending on the pH of the solution it is in

acidic

describes a solution in which [H₃O⁺] > [OH⁻]

amphiprotic

species that may either gain or lose a proton in a reaction

amphoteric

species that can act as either an acid or a base

autoionization

reaction between identical species yielding ionic products; for water, this reaction involves transfer of protons to yield hydronium and hydroxide ions

base ionization

reaction involving the transfer of a proton from water to a base, yielding hydroxide ions and the conjugate acid of the base

base ionization constant (K_b)

equilibrium constant for the ionization of a weak base

basic

describes a solution in which [H₃O⁺] < [OH⁻]

Brønsted-Lowry acid

proton donor

Brønsted-Lowry base

proton acceptor

buffer

mixture of a weak acid or a weak base and the salt of its conjugate; the pH of a buffer resists change when small amounts of acid or base are added

buffer capacity

amount of an acid or base that can be added to a volume of a buffer solution before its pH changes significantly (usually by one pH unit)

color-change interval

range in pH over which the color change of an indicator takes place

conjugate acid

substance formed when a base gains a proton

conjugate base

substance formed when an acid loses a proton

diprotic acid

acid containing two ionizable hydrogen atoms per molecule. A diprotic acid ionizes in two steps

diprotic base

base capable of accepting two protons. The protons are accepted in two steps

Henderson-Hasselbalch equation

equation used to calculate the pH of buffer solutions

ion-product constant for water (K_w)

equilibrium constant for the autoionization of water

leveling effect of water

any acid stronger than ${\text{H}}_3{\text{O}}^{\text{+}},$ or any base stronger than OH⁻ will react with water to form ${\text{H}}_3{\text{O}}^{\text{+}},$ or OH⁻, respectively; water acts as a base to make all strong acids appear equally strong, and it acts as an acid to make all strong bases appear equally strong

monoprotic acid

acid containing one ionizable hydrogen atom per molecule

neutral

describes a solution in which [H₃O⁺] = [OH⁻]

oxyacid

compound containing a nonmetal and one or more hydroxyl groups

percent ionization

ratio of the concentration of the ionized acid to the initial acid concentration, times 100

pH

logarithmic measure of the concentration of hydronium ions in a solution

pOH

logarithmic measure of the concentration of hydroxide ions in a solution

stepwise ionization

process in which an acid is ionized by losing protons sequentially

titration curve

plot of the pH of a solution of acid or base versus the volume of base or acid added during a titration

triprotic acid

acid that contains three ionizable hydrogen atoms per molecule; ionization of triprotic acids occurs in three steps