111 exam-style questions on Proton transfer reactions (acids and bases) — topic R3.1 of Reactivity 3: What are the mechanisms of chemical change? in the IB Chemistry syllabus — with answers and explanations. Samples below; the full set is free with an account.
A solution has a pH of 3. Compared with a solution of pH 5, it is
Answer: 100 times more acidic
pH is logarithmic: each unit is a factor of 10 in [H⁺], so pH 3 has 100× the H⁺ concentration of pH 5.
Which of the following is a strong acid?
Answer: hydrochloric acid
Hydrochloric acid is essentially fully dissociated in water. Ethanoic and carbonic acids are weak acids, and ammonia is a weak base.
According to Brønsted–Lowry theory, identify the conjugate acid of water, H₂O.
Answer: H₃O⁺
A conjugate acid is formed by gaining a proton; H₂O + H⁺ → H₃O⁺.
Identify the statement that distinguishes a strong acid from a weak acid of the same concentration.
Answer: A strong acid dissociates completely, so it has a higher [H⁺] and lower pH
Strong acids ionise completely, giving a higher [H⁺] and thus a lower pH than a weak acid of equal concentration.
Solution X is 0.10 mol dm⁻³ hydrochloric acid and solution Y is 1.0 mol dm⁻³ ethanoic acid. Identify the statement that uses the terms strong and concentrated correctly.
Answer: X is the more dilute solution but the stronger acid
Strength describes the extent of dissociation, which is a property of the acid, while concentration describes how much acid was dissolved. Hydrochloric acid dissociates fully whatever its concentration, so X is strong and dilute while Y is weak and concentrated.
Identify the conjugate base of the hydrogensulfate ion, HSO₄⁻(aq).
Answer: SO₄²⁻(aq)
A conjugate base is what remains after the species donates one proton, so HSO₄⁻ loses H⁺ to give SO₄²⁻. Choosing H₂SO₄ gives the conjugate acid instead — the direction of proton transfer must be checked every time.
That was 6 of 111 Proton transfer reactions (acids and bases) questions.
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111 Proton transfer reactions (acids and bases) questions — free with an account. Spaced repetition, streaks and full exam simulations included.
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