A-Level Chemistry: Acids, Bases and Buffers

The acids-and-bases topic is the purest test of method in A-Level Chemistry: every question type has a standard calculation route, and the marks go to those who execute it exactly. This quiz covers all the routes, with every pH value worked in full.

The conceptual layer covers Brønsted-Lowry theory through proton-acceptor identification and conjugate acid-base pairs — species differing by exactly one proton. The calculation layer then works through the canonical cases: strong base pH via pOH and Kw (0.025 mol dm⁻³ NaOH landing at pH 12.40), weak acid pH via the Ka approximation (√(Ka·C) giving pH 2.5 for the standard 0.10 mol dm⁻³ case), a direct [H⁺] computation from Ka, and the pKa conversion (−log of 1.5 × 10⁻⁵ giving 4.82).

Titration analysis is covered from curve shape to indicator logic: which of the four strong/weak combinations gives an equivalence point at exactly pH 7, why the weak–weak combination produces no sharp vertical section and is effectively untitratable with an indicator, and which indicators suit a weak acid–strong base titration — where both phenolphthalein and thymol blue's basic transition qualify, a deliberately precise multi-select.

Buffers close the set with the mechanism itself: how the acetic acid/acetate reservoir consumes added H⁺ and OH⁻, and which way the equilibrium shifts on each addition.

Explanations show the log arithmetic in full each time. Paired with the Equilibria quiz in this collection, this set completes the Year 2 physical chemistry calculation core.

• Identify Brønsted-Lowry acids, bases and conjugate pairs
• Calculate pH for strong acids, strong bases and weak acids
• Convert between Ka and pKa fluently
• Match titration curve shapes and indicators to acid-base combinations
• Explain buffer action through the equilibrium mechanism

Aligned to the acid-base content of the DfE A level science subject content as delivered in current specifications: Brønsted-Lowry theory, pH and Ka calculations, Kw, titration curves, indicators and buffers.