Quick answer: A strong acid ionises completely, so its pH comes straight from its concentration. This AP Chemistry test on acids and bases pH has 8 questions worth 20 marks, to do in 45 minutes: Brønsted–Lowry base, strong acid pH and weak acid calculation. The mark scheme is on a separate page; free printable PDF.
Answer all questions. Show your working and give pH values to two decimal places. A calculator is allowed. Use Ka(CH₃COOH) = 1.8 × 10⁻⁵ and Kw = 1.0 × 10⁻¹⁴ unless the question gives other data.
Level: AP Chemistry · Curriculum: AP Chem Unit 8
Question 1 Brønsted–Lowry base (2 marks)
- Define a Brønsted–Lowry base. (1 mark)
- State the conjugate acid of NH₃. (1 mark)
Question 2 Strong acid pH (2 marks)
Kofi dissolves hydrogen iodide in water to give 0.0042 mol/dm³ HI(aq). Determine the pH of the solution. (2 marks)Question 3 Weak acid calculation (3 marks)
Calculate the pH of 0.250 mol/dm³ CH₃COOH, Ka = 1.8 × 10⁻⁵. (3 marks)Question 4 Equal neutralisation (2 marks)
0.10 mol/dm³ HCl and 0.10 mol/dm³ HF have different pH values, yet 20.0 cm³ of each needs the same volume of NaOH. Explain both observations. (2 marks)Question 5 Weak base calculation (3 marks)
- Calculate the pH of 0.150 mol/dm³ NH₃, Kb = 1.8 × 10⁻⁵. (2 marks)
- Calculate Ka of NH₄⁺. (1 mark)
Question 6 Comparing pH values (2 marks)
Solution A has pH 3 and solution B has pH 5. Calculate how many times larger [H₃O⁺] is in A and state which is more acidic. (2 marks)Question 7 Ranking three acids (3 marks)
- Rank the acids from strongest to weakest. (1 mark)
- Calculate Ka of acid P. (2 marks)
Question 8 Acidic and basic salts (3 marks)
Write ionic equations to explain why a solution of NH₄Cl is acidic and a solution of CH₃COONa is basic. (3 marks)
