Acids, Bases & Salts — 60 Terms Defined

Acid Acids, Bases & Salts Dimensionless A substance that donates protons, produces hydrogen ions in water, or accepts a pair of electrons. HA → H⁺ + A⁻

Acid Dissociation Constant Acids, Bases & Salts mol/L The equilibrium constant for the ionisation of an acid in water, measuring its strength. Ka = [H⁺][A⁻] / [HA]

Acid Strength and Molecular Structure Acids, Bases & Salts Dimensionless The structural factors that determine how readily a molecule releases a proton.

Acidic Buffer Acids, Bases & Salts Dimensionless A buffer made from a weak acid and one of its salts, giving a pH below 7. pH = pKa + log([salt]/[acid])

Acidic Salt Acids, Bases & Salts Dimensionless A salt whose aqueous solution has a pH below 7, or one that still contains replaceable hydrogen.

Acidic Solution Acids, Bases & Salts mol/L A solution in which the hydrogen ion concentration exceeds the hydroxide ion concentration. [H⁺] > [OH⁻]

Acid–Base Indicator Acids, Bases & Salts Dimensionless A weak acid or base whose conjugate forms have distinctly different colours, used to signal the end point of a titration. HIn ⇌ H⁺ + In⁻

Acid–Base Titration Acids, Bases & Salts mol/L A titration in which an acid is neutralised by a base, or the reverse, monitored by an indicator or a pH meter. M_aV_a / n_a = M_bV_b / n_b

Amphiprotic Species Acids, Bases & Salts Dimensionless A species that can both donate and accept a proton.

Amphoteric Substance Acids, Bases & Salts Dimensionless A substance able to react as either an acid or a base depending on what it meets.

Arrhenius Theory Acids, Bases & Salts Dimensionless The theory defining an acid as a substance that produces H⁺ ions in water and a base as one that produces OH⁻ ions. HA → H⁺ + A⁻; BOH → B⁺ + OH⁻

Base Acids, Bases & Salts Dimensionless A substance that accepts protons, produces hydroxide ions in water, or donates a pair of electrons. B + H⁺ → BH⁺

Base Dissociation Constant Acids, Bases & Salts mol/L The equilibrium constant for the reaction of a base with water to produce hydroxide ions. Kb = [BH⁺][OH⁻] / [B]

Basic Buffer Acids, Bases & Salts Dimensionless A buffer made from a weak base and one of its salts, giving a pH above 7. pOH = pKb + log([salt]/[base])

Basic Salt Acids, Bases & Salts Dimensionless A salt whose aqueous solution has a pH above 7, or one that retains a hydroxide group.

Basic Solution Acids, Bases & Salts mol/L A solution in which the hydroxide ion concentration exceeds the hydrogen ion concentration. [OH⁻] > [H⁺]

Brønsted–Lowry Theory Acids, Bases & Salts Dimensionless The theory defining an acid as a proton donor and a base as a proton acceptor. HA + B ⇌ A⁻ + BH⁺

Buffer Capacity Acids, Bases & Salts mol/L The amount of strong acid or base a buffer can absorb before its pH changes appreciably. β = dn / d(pH)

Buffer Range Acids, Bases & Salts Dimensionless The span of pH values over which a buffer works effectively, conventionally one unit either side of its pKa. pH = pKa ± 1

Buffer Solution Acids, Bases & Salts Dimensionless A solution that resists changes in pH when small amounts of acid or base are added.

Complex Salt Acids, Bases & Salts Dimensionless A salt containing a complex ion that retains its identity in solution rather than dissociating into simpler ions. e.g. K₄[Fe(CN)₆]

Conjugate Acid–Base Pair Acids, Bases & Salts Dimensionless Two species differing by exactly one proton, one being the acid and the other its corresponding base. HA / A⁻

Degree of Hydrolysis Acids, Bases & Salts Dimensionless The fraction of a salt's ions that have reacted with water at equilibrium. h = √(Kh / c)

Degree of Ionisation Acids, Bases & Salts Dimensionless The fraction of dissolved electrolyte molecules that have broken into ions at equilibrium. α = ionised / total