Acids & Bases is one of 10 topics in the Grade 12 Physical Sciences CAPS syllabus, covered across 4 lessons on Study Vault. Below are real practice questions from this topic with full worked answers.
Sample practice questions
Easy
1. According to the Lowry-Bronsted definition, an acid is:
A proton (H+) donor
A proton (H+) acceptor
A substance that produces OH- ions
A substance that turns litmus blue
Answer: A proton (H+) donor — The Lowry-Bronsted definition describes an acid as any species that donates a proton (H+) to another species in a reaction.
Easy
2. A strong acid is one that:
Ionises almost completely in water
Is present in high concentration
Has a very low pH always
Reacts violently with metals
Answer: Ionises almost completely in water — Strength refers to the degree of ionisation: a strong acid ionises ~100% in aqueous solution, regardless of how concentrated the solution is.
Medium
3. In the reaction NH3+H2O⇌NH4++OH−, identify the conjugate acid-base pair that includes NH3.
NH3 (base) / NH4+ (its conjugate acid)
NH3 (acid) / OH- (its conjugate base)
NH3 (base) / H2O (its conjugate acid)
NH3 (acid) / NH4+ (its conjugate base)
Answer: NH3 (base) / NH4+ (its conjugate acid) — NH3 accepts a proton to become NH4+, so NH3 is the base and NH4+ is its conjugate acid (they differ by exactly one H+).
