Acids, bases and buffers: key terms
8 terms. Say the definition out loud, tap to check, then say whether you knew it. Back to the topic
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Brønsted–Lowry acid
A species that donates a proton, H⁺.
Examiners say A Brønsted–Lowry base accepts a proton.
Conjugate acid–base pair
Two species that can be interconverted by the transfer of a proton.
Examiners say Label the pairs as acid 1/base 1 and acid 2/base 2: each pair differs by one H⁺.
Strong acid
An acid that dissociates completely in aqueous solution.
Examiners say A weak acid dissociates only partially. Strength is not the same as concentration.
pH
pH = –log[H⁺(aq)]; [H⁺(aq)] = 10^–pH.
Examiners say Give pH to two decimal places unless told otherwise.
Acid dissociation constant, Ka
Ka = [H⁺][A⁻] ÷ [HA] for a weak acid HA. pKa = –log Ka.
Examiners say The larger the Ka (the smaller the pKa), the stronger the acid. The approximations are that [H⁺] = [A⁻] and that [HA] at equilibrium equals its original concentration.
Ionic product of water, Kw
Kw = [H⁺][OH⁻] = 1.00 × 10⁻¹⁴ mol² dm⁻⁶ at 298 K.
Examiners say Use it to find the pH of a strong base: [H⁺] = Kw ÷ [OH⁻].
Buffer solution
A system that minimises pH changes on the addition of small amounts of an acid or a base.
Examiners say "Minimises", not "prevents". Made from a weak acid and its salt, or from excess weak acid and a strong alkali.
Equivalence point
The point in a titration at which the acid and base have reacted exactly in the mole ratio of the equation.
Examiners say It is the centre of the vertical section of the pH curve. An indicator is suitable if its pH range lies within that vertical section.
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