Proton Theory: Acids as Proton Donors
15 Questions · 34 Total Marks · Sections A, B & C
Section A
Definitions
5 questions · 10 marks
Section B
Application
5 questions · 11 marks
Section C
Explanations
5 questions · 13 marks
Define an acid in terms of proton transfer.
Think about what an acid does to H⁺ ions during a reaction.
Define a base in terms of proton transfer.
A base does the opposite of an acid.
Explain what is meant by the term 'conjugate acid-base pair'.
What is left behind after an acid donates a proton?
Define an amphoteric substance in terms of proton theory.
Which substance can both donate AND accept a proton?
State the difference between a 'strong acid' and a 'weak acid' in terms of proton donation.
Think about how completely the acid donates its protons.
In the reaction: HCl(aq) + H₂O(l) → H₃O⁺(aq) + Cl⁻(aq) Identify the proton donor and the proton acceptor. Explain your reasoning.
Which substance loses H⁺? Which substance gains H⁺?
In the reaction: NH₃(g) + H₂O(l) ⇌ NH₄⁺(aq) + OH⁻(aq) Explain the role of water in this reaction in terms of proton theory.
Is water gaining or losing an H⁺ here? Compare this to Question 6.
Consider the reaction: CH₃COOH(aq) + H₂O(l) ⇌ CH₃COO⁻(aq) + H₃O⁺(aq) (a) Identify the two conjugate acid-base pairs in this equilibrium. (b) State whether ethanoic acid is a strong or weak acid, giving evidence from the equation.
Look for the two species that differ by one H⁺ each.
Ammonia (NH₃) is described as a base in the Brønsted-Lowry theory. Explain why, using the equation for its reaction with hydrochloric acid.
Write the equation first, then identify what NH₃ does to H⁺.
The hydrogen carbonate ion (HCO₃⁻) can react with both acids and bases: • With acid: HCO₃⁻ + H⁺ → H₂CO₃ • With base: HCO₃⁻ + OH⁻ → CO₃²⁻ + H₂O Using proton theory, explain why HCO₃⁻ is described as amphoteric.
Does HCO₃⁻ act as an acid in one reaction and a base in the other?
Explain why an H⁺ ion is often referred to simply as 'a proton'.
Think about the structure of a hydrogen atom: what does it contain?
Hydrochloric acid (HCl) and ethanoic acid (CH₃COOH) are both acids with the same concentration (1 mol/dm³). (a) Explain which solution has the lower pH. (b) Explain the difference in terms of proton donation.
One acid fully donates, one partially donates. Which gives more H⁺ ions?
Explain why the dissolving of HCl in water can be described as an acid-base reaction, even though no salt is visibly formed.
What is transferred between HCl and H₂O?
A student says: 'An acid always produces H⁺ ions in solution, so any substance that lowers pH must be an acid.' Evaluate this statement using proton theory.
Is the student's definition complete? Can other substances lower pH without being proton donors?
Sulfuric acid (H₂SO₄) is described as a diprotic acid. (a) Explain the meaning of 'diprotic'. (b) Write two equations to show the stepwise donation of protons by H₂SO₄ in water. (c) Suggest why the second proton donation is less complete than the first.
After the first proton is donated, what charge does the remaining ion carry?
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