A solution has a pH of 3. Calculate the hydrogen ion concentration in mol/dm3.

The calculated answer is 0.001 mol/dm3.

This uses Concentration in mol/dm3 because the objective is about (HT only) Explain that a lower pH means a higher hydrogen ion concentration. This exam wording variant asks students to separate HT only from similar Unit 4.4 chemical-change ideas. The reasoning belongs to Strong and weak acids (HT only) within Reactions of acids, so it should not be confused with nearby ideas about acids, alkalis, bases, oxidation, reduction, displacement, reactivity, electrolysis, electrodes, ions, pH, or salt preparation unless those are named in the objective. Use the focus term HT only to keep the answer aligned with AQA GCSE Chemistry 8462 Unit 4.4 Chemical changes. Keep acid, alkali and base distinct; keep oxidation and reduction distinct; do not mix reduction with displacement; keep electrolysis separate from electroplating; distinguish anode from cathode, positive ions from negative ions, oxidation state from ionic charge, and strong acid from concentrated acid.