WJEC A Level Chemistry
WJEC A Level Chemistry 3.9 Acid-base Equilibria Exam Questions
Free WJEC A Level Chemistry exam questions on 3.9 Acid-base Equilibria, with mark schemes. Covers Ka, pH of weak acids, Kw, buffers and titration curves.
3.9 Acid-base Equilibria exam questions
1 question pack of real past exam questions with its mark scheme. Answer every question without notes, then mark your answers line by line against the mark scheme.
StemUp mark scheme flashcards
WJEC A Level Chemistry Flashcards (Anki & Quizlet)
Every answer is written in mark scheme wording, so you learn exactly what examiners give marks for. Use them on Anki or Quizlet, then test yourself with the questions on this page.
£16.99View flashcards
About WJEC A Level Chemistry 3.9 Acid-base Equilibria
This topic covers quantitative acid-base chemistry.
What you need to know
- Weak acids Ka = [H⁺][A⁻] / [HA]; pH from Ka and concentration.
- Kw Kw = [H⁺][OH⁻] = 1.0 x 10⁻¹⁴ at 298 K; pH of strong bases.
- Buffers Resist pH change; pH = pKa when [HA] = [A⁻].
- Titration curves Shapes for strong and weak acids and bases, and choosing indicators.
Common mistakes in 3.9 Acid-base Equilibria
- Using pH = −log of concentration for weak acids.
- Forgetting Kw changes with temperature.
- Choosing an indicator outside the vertical section.
Try three 3.9 Acid-base Equilibria exam-style questions
1. Calculate the pH of 0.10 mol dm⁻³ ethanoic acid (Ka = 1.7 x 10⁻⁵). (2 marks)
Show the mark scheme answer
[H⁺] = √(1.7 x 10⁻⁶) = 1.30 x 10⁻³ (1); pH = 2.89 (1).
2. Explain how an ethanoate buffer resists added acid. (2 marks)
Show the mark scheme answer
Added H⁺ reacts with ethanoate ions to form ethanoic acid (1), so [H⁺] changes very little (1).
3. State the pH of a neutral solution at 298 K. (1 mark)
Show the mark scheme answer
7.
3.9 Acid-base Equilibria FAQs
What does Acid-base Equilibria cover?
Ka, Kw, pH calculations, buffers and titration curves.
Which practical links here?
Measuring titration curves with a pH meter.
How is buffer pH calculated?
[H⁺] = Ka x [HA] / [A⁻].
Revise this topic with flashcards: WJEC A Level Chemistry Flashcards, with mark scheme answers for Anki and Quizlet.
