A complete revision and exam practice pack for SC8b Looking at Acids, covering C3.5H, C3.7H and C3.8H. This is an entirely Higher-tier topic.

Topic Mastery Sheet (PDF) - a comprehensive student reference built around the two key distinctions that students consistently confuse: strong vs weak, and concentrated vs dilute. These are completely independent properties. The concentrated/dilute distinction is explained in terms of amount of solute per unit volume. The strong/weak distinction is explained through the degree of dissociation into ions: a strong acid (hydrochloric, sulfuric, nitric) completely dissociates in water, producing the maximum possible H⁺ concentration for a given amount of acid; a weak acid (ethanoic, citric, carbonic) only partially dissociates, leaving most molecules intact. A four-row table shows all combinations - concentrated strong, dilute strong, concentrated weak, dilute weak - with their relative H⁺ concentrations, pH values and reactivity. The critical insight for the Higher Level of Response question is developed carefully: reactivity depends on H⁺ concentration alone, not on the total acid present. This means a sufficiently concentrated weak acid can have exactly the same H⁺ concentration as a dilute strong acid - and therefore react at exactly the same rate. This is the explanation for why dilute HCl and concentrated ethanoic acid can produce hydrogen gas from magnesium in the same time. The stretch section introduces the acid dissociation constant Ka and pKa.

Student Exam Practice Sheet (PDF + DOCX) - five questions (13 marks), all Higher tier: concentrated vs dilute explanation, strong vs weak acid explanation, which of HCl or ethanoic acid has lower pH at the same concentration, an H⁺ concentration MCQ (pH 3 vs pH 5 = 100× difference), and the full 6-mark Level of Response question on why magnesium reacts at the same rate in dilute HCl and concentrated ethanoic acid, with a complete three-level mark scheme and full indicative content.

Teacher Answer Key (PDF + DOCX) - full Level of Response mark scheme with indicative content.

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