Quick answer: A strong acid ionises completely, so its pH comes straight from its concentration. This AP Chemistry worksheet on acids and bases pH gives 20 problems from easy to hard: pH of a strong acid, pH of a strong base and hydronium from pH. The worked answers are on a separate page, and the worksheet is a free printable PDF.
These problems train the full toolkit for Unit 8 of AP Chemistry: pH and pOH, strong and weak acids and bases, Ka and Kb, and the 5 % check. They also suit first-year university and A Level chemistry.
Start with the level 1 problems, which use logarithms and strong species. Level 2 problems need ICE tables, and the last five are level 3 problems with approximations that can fail, mixtures and explanations.
Level: AP Chemistry · Curriculum: AP Chem Unit 8
Problem 1 pH of a strong acid ★★★
Aarav in Pune prepares 0.0100 mol/dm³ HCl for a school titration.1. Calculate [H₃O⁺].
2. Calculate the pH.
Problem 2 pH of a strong base ★★★
Chiamaka in Lagos dissolves NaOH to make 0.0030 mol/dm³.1. Calculate pOH.
2. Calculate pH at 25 °C.
Problem 3 Hydronium from pH ★★★
A rainwater sample in Leeds has pH 3.40.2. State how many times larger it is than in neutral water at 25 °C.
Problem 4 Classify the species ★★★
Classify each as strong acid, weak acid, strong base or weak base: HNO₃, HF, NH₃, KOH, CH₃COOH, HBr.Problem 5 Calcium hydroxide ★★★
Diego in Texas makes 0.050 mol/dm³ Ca(OH)₂ solution.1. Calculate [OH⁻].
2. Calculate the pH.
Problem 6 Conjugate pairs ★★★
In the reaction HCO₃⁻ + NH₃ ⇌ CO₃²⁻ + NH₄⁺, identify the two conjugate acid–base pairs.Problem 7 Dilution of a strong acid ★★★
Emma in Leeds pipettes 10.0 cm³ of 0.50 mol/dm³ HCl into a 500 cm³ volumetric flask and fills to the mark.1. Calculate the new concentration.
2. Calculate the pH.
Problem 8 Neutral water at 50 °C ★★★
At 50 °C, Kw = 5.5 × 10⁻¹⁴.1. Calculate [H₃O⁺] in pure water.
2. Calculate its pH.
3. Explain why the water is still neutral although pH is not 7.
Problem 9 Hydrocyanic acid ★★★
HCN is a weak acid with Ka = 4.9 × 10⁻¹⁰. Calculate the pH of a 0.10 mol/dm³ solution.Problem 10 Fluoride as a base ★★★
The Ka of HF is 6.8 × 10⁻⁴.1. Calculate pKa of HF.
2. Calculate Kb of F⁻.
3. Calculate pKb of F⁻.
Problem 11 HCl against ethanoic acid ★★★
Compare 0.10 mol/dm³ HCl with 0.10 mol/dm³ CH₃COOH (Ka = 1.8 × 10⁻⁵).1. Calculate the pH of each.
2. Explain why 25.0 cm³ of each needs the same volume of 0.10 mol/dm³ NaOH to neutralise.
Problem 12 Ka from a pH reading ★★★
A student measures pH 3.00 for 0.100 mol/dm³ of a weak monoprotic acid HA.1. Calculate [H₃O⁺].
2. Calculate Ka.
Problem 13 Percent ionisation of HF ★★★
Wanjiru in Nairobi prepares 0.500 mol/dm³ HF (Ka = 6.8 × 10⁻⁴).1. Calculate [H₃O⁺] with the shortcut.
2. Calculate the pH.
3. Calculate the percent ionisation.
Problem 14 Methylamine ★★★
CH₃NH₂ is a weak base with Kb = 4.4 × 10⁻⁴. Calculate the pH of a 0.40 mol/dm³ solution.Problem 15 Ammonium chloride solution ★★★
Bilal in Lahore dissolves NH₄Cl to make 0.10 mol/dm³. Kb of NH₃ is 1.8 × 10⁻⁵.1. Calculate Ka of NH₄⁺.
2. Calculate the pH.
Problem 16 Mixing acid and base ★★★
Mei in Singapore mixes 25.0 cm³ of 0.100 mol/dm³ HCl with 15.0 cm³ of 0.200 mol/dm³ NaOH.2. Identify which is in excess and by how much.
3. Calculate the final pH.
Problem 17 When the shortcut fails ★★★
Calculate the pH of 0.0100 mol/dm³ HF (Ka = 6.8 × 10⁻⁴) in two ways.1. Use x = √(Ka × C) and test the 5 % rule.
2. Solve the quadratic and compare the two pH values.
Problem 18 Very dilute acid ★★★
A student states that 1.0 × 10⁻⁸ mol/dm³ HCl has pH 8.00.1. Explain why the claim cannot be right.
2. Calculate the actual pH, including the water ionisation.
Problem 19 Two weak acids ★★★
Acid X has pKa 4.20 and acid Y has pKa 5.60. Both solutions are 0.20 mol/dm³.2. Calculate the pH of each.
3. Calculate the ratio [H₃O⁺]X / [H₃O⁺]Y and explain it.
Problem 20 Dilution and ionisation ★★★
Kofi in Accra dilutes 0.100 mol/dm³ ethanoic acid (Ka = 1.8 × 10⁻⁵) tenfold to 0.0100 mol/dm³.1. Calculate the pH before and after dilution.
2. Calculate the percent ionisation before and after.
3. Explain the trend using Le Chatelier’s principle or Q.
