• 54 questions

AP Chemistry Acid Base Practice Test

Unofficial multiple-choice practice for Unit 8 of AP Chemistry, Acids and Bases: pH, weak acids, buffers and titration curves.

At 25 °C a solution has [H₃O⁺] = 2.5 × 10⁻⁴ M. What is its pH?

Pick an answer, then press Check answer. Then you see Correct or Not quite, with the reason. Keys: A to D pick, Enter checks.

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Unofficial practice questions, not affiliated with the College Board. Bank checked October 9, 2026.

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All 54 questions

Topic 8.1: Introduction to acids and bases 5

  • At 25 °C a solution has [H₃O⁺] = 2.5 × 10⁻⁴ M. What is its pH? Purdue University, General Chemistry Topic Review, "pH, pOH, and Ka"; course topic 8.1
  • At 25 °C a solution has [H₃O⁺] = 4.0 × 10⁻⁹ M. What is its hydroxide ion concentration? Purdue University, General Chemistry Topic Review, "pH, pOH, and Ka"; course topic 8.1
  • At 25 °C a solution has a pOH of 3.20. What is its pH? Purdue University, General Chemistry Topic Review, "pH, pOH, and Ka"; course topic 8.1
  • At 50 °C the value of pKw is 13.26. What is the pH of pure water at 50 °C, and is the water acidic, basic or neutral? Wikipedia, "Self-ionization of water" and "pH"; course topic 8.1
  • Which statement is true of a neutral aqueous solution at every temperature? Purdue University, General Chemistry Topic Review, "pH, pOH, and Ka"; Wikipedia, "Self-ionization of water"; course topic 8.1
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Topic 8.2: pH and pOH of strong acids and bases 5

  • A chemist dilutes 10.0 mL of 0.10 M HCl with water to a total volume of 1.00 L. What is the pH of the diluted acid? Purdue University, General Chemistry Topic Review, "Solving Equilibrium Problems Involving Strong Acids"; course topic 8.2
  • A solution of a strong acid has a pH of 1.70. What is its hydronium ion concentration? Purdue University, General Chemistry Topic Review, "pH, pOH, and Ka"; course topic 8.2
  • Calcium hydroxide is a strong base: Ca(OH)₂ → Ca²⁺ + 2 OH⁻. What is the pH of 0.0050 M Ca(OH)₂ at 25 °C? Wikipedia, "Calcium hydroxide"; Purdue University, General Chemistry Topic Review, "pH, pOH, and Ka"; course topic 8.2
  • Nitric acid is a strong acid. What is the pH of 0.0050 M HNO₃? Purdue University, General Chemistry Topic Review, "Solving Equilibrium Problems Involving Strong Acids" and "pH, pOH, and Ka"; course topic 8.2
  • Which statement describes 0.10 M hydrochloric acid at equilibrium? Purdue University, General Chemistry Topic Review, "pH, pOH, and Ka"; course topic 8.2

Topic 8.3: Weak acid and base equilibria 8

  • Ammonia has Kb = 1.8 × 10⁻⁵. What is the pH of 0.40 M NH₃ at 25 °C? Purdue University, General Chemistry Topic Review, "Solving Equilibrium Problems Involving Bases"; course topic 8.3
  • An unknown monoprotic acid is made up at 0.20 M, and the pH is measured as 2.70. What is the acid's Ka? Purdue University, General Chemistry Topic Review, "pH, pOH, and Ka"; course topic 8.3
  • Find the pH of 0.25 M acetic acid, for which Ka = 1.8 × 10⁻⁵. Purdue University, General Chemistry Topic Review, "pH, pOH, and Ka"; course topic 8.3
  • For an acid with Ka = 1.0 × 10⁻⁵, about what percent is ionized at 0.10 M, and at 0.0010 M? Purdue University, General Chemistry Topic Review, "pH, pOH, and Ka"; course topic 8.3
  • Formic acid has pKa = 3.75 and acetic acid has pKa = 4.76. How do the two acids compare? Purdue University, General Chemistry Topic Review, "Solubility Product" and "pH, pOH, and Ka"; Wikipedia, "Formic acid" and "Acetic acid"; course topic 8.3
  • Hydrofluoric acid, HF, has Ka = 6.6 × 10⁻⁴ at 25 °C. What is Kb for its conjugate base, the fluoride ion? Wikipedia, "Hydrofluoric acid" and "Acid strength"; course topic 8.3
  • In 0.10 M acetic acid at equilibrium, about what share of the acetic acid molecules have lost a proton to water? Purdue University, General Chemistry Topic Review, "pH, pOH, and Ka"; course topic 8.3
  • The pH of a 0.10 M solution of a weak monoprotic acid is 3.00. What percent of the acid molecules have ionized? Purdue University, General Chemistry Topic Review, "pH, pOH, and Ka"; course topic 8.3

Topic 8.4: Acid-base reactions and buffers 4

  • A 0.10 M solution of sodium acetate, the salt formed when acetic acid is exactly neutralized by NaOH, has a pH of about 8.9. Why is it basic? Purdue University, General Chemistry Topic Review, "Mixtures and Buffers" and "Solving Equilibrium Problems Involving Bases"; course topic 8.4
  • A chemist mixes 50.0 mL of 0.200 M HCl with 50.0 mL of 0.100 M NaOH. What is the pH of the mixture? Wikipedia, "Neutralization (chemistry)"; Purdue University, General Chemistry Topic Review, "pH, pOH, and Ka"; course topic 8.4
  • To 1.0 L of water are added 0.050 mol of a weak acid HA and 0.080 mol of NaOH. What is the pH at 25 °C? Purdue University, General Chemistry Topic Review, "pH, pOH, and Ka" and "Mixtures and Buffers"; course topic 8.4
  • To 1.0 L of water are added 0.10 mol of acetic acid and 0.040 mol of NaOH. Besides water and Na⁺, which species are present in the largest amounts once the reaction is over? Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; course topic 8.4

Topic 8.5: Acid-base titrations 7

  • A 20.0 mL sample of acetic acid reaches its equivalence point after 16.0 mL of 0.150 M NaOH has been added. What was the concentration of the acetic acid? Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; course topic 8.5
  • A diprotic acid H₂A is titrated with NaOH, and the first equivalence point comes at 10.0 mL. At which volumes do the second equivalence point and the point where pH = pKa₂ fall? Wikipedia, "Titration curve"; course topic 8.5
  • How many equivalence points appear when a strong base titrates a diprotic acid? Wikipedia, "Acid"; course topic 8.5
  • In a titration with NaOH, a weak acid reaches its equivalence point at 24.0 mL of base. When 12.0 mL had been added, the pH was 4.20. What is the acid's pKa? Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; Wikipedia, "Acid dissociation constant"; course topic 8.5
  • In the titration of acetic acid with NaOH, the pH climbs only slowly through the middle of the curve, before the equivalence point. Why? Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; course topic 8.5
  • What is plotted on the two axes of an acid-base titration curve? Wikipedia, "Titration curve"; course topic 8.5
  • Which titration has an equivalence point below pH 7? Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; course topic 8.5

Topic 8.6: Molecular structure of acids and bases 5

  • Acetic acid, CH₃COOH, has four hydrogen atoms. Which one is donated when it acts as an acid? Wikipedia, "Carboxylic acid"; course topic 8.6
  • Chloroacetic acid, ClCH₂COOH, has pKa = 2.86, and acetic acid, CH₃COOH, has pKa = 4.76. What accounts for the difference? Wikipedia, "Acid strength", "Chloroacetic acid" and "Acetic acid"; course topic 8.6
  • HOCl, HOBr and HOI each have one oxygen atom bonded to the halogen. Which is the strongest acid, and why? Wikipedia, "Oxyacid"; PubChem periodic table, National Library of Medicine; course topic 8.6
  • Which of these compounds is a weak base in water? Purdue University, General Chemistry Topic Review, "Solubility Product"; Wikipedia, "Hydroxide" and "Weak base"; course topic 8.6
  • Which of these oxyacids of chlorine is the strongest acid? Wikipedia, "Oxyacid" and "Acid strength"; course topic 8.6

Topic 8.7: pH and pKa 5

  • A student titrates acetic acid with NaOH using methyl orange, which changes color between pH 3.1 and 4.4. How does the endpoint compare with the equivalence point? Wikipedia, "pH indicator"; Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; course topic 8.7
  • Acetic acid has pKa = 4.76. In a solution held at pH 3.00, which form is present in the higher concentration? Wikipedia, "Acid dissociation constant" and "Acetic acid"; course topic 8.7
  • An acid has pKa = 7.20. In a solution held at pH 6.20, what is the ratio of its base form, A⁻, to its acid form, HA? Wikipedia, "Henderson–Hasselbalch equation"; course topic 8.7
  • What kind of substance is an acid-base indicator? Wikipedia, "pH indicator"; course topic 8.7
  • When acetic acid is titrated with NaOH, the solution at the equivalence point is basic, with a pH between 8 and 9. Which indicator is the best choice? Wikipedia, "pH indicator"; Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; course topic 8.7

Topic 8.8: Properties of buffers 4

  • A buffer contains ammonia, NH₃, and ammonium chloride, NH₄Cl. A little hydrochloric acid is added. Which species reacts with the added H₃O⁺? Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; course topic 8.8
  • A small amount of NaOH is added to a buffer of acetic acid and acetate ion. Which reaction uses up the added hydroxide? Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; course topic 8.8
  • Adding 0.01 mol of HCl to a liter of water drops the pH from 7 to 2. Adding it to a liter of buffer that is 0.10 M in acetic acid and in acetate changes the pH only from 4.74 to 4.66. Why? Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; course topic 8.8
  • Which pair of solutes, dissolved together in water, makes a buffer? Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; course topic 8.8

Topic 8.9: Henderson-Hasselbalch equation 5

  • A buffer at pH 5.00 is to be made from a weak acid with pKa = 4.70. What ratio of [A⁻] to [HA] is needed? Wikipedia, "Henderson–Hasselbalch equation"; course topic 8.9
  • A buffer contains more of the weak acid HA than of its conjugate base A⁻. How does its pH compare with the pKa of HA? Wikipedia, "Henderson–Hasselbalch equation" and "Acid dissociation constant"; course topic 8.9
  • A buffer is 0.30 M in NH₃ and 0.15 M in NH₄Cl. The ammonium ion has pKa = 9.25. What is the pH? Wikipedia, "Henderson–Hasselbalch equation" and "Ammonium"; Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; course topic 8.9
  • A buffer of acetic acid and sodium acetate is diluted with an equal volume of pure water. What happens to its pH? Wikipedia, "Buffer solution"; course topic 8.9
  • Find the pH of a solution that is 0.10 M in formic acid (pKa = 3.75) and 0.50 M in sodium formate. Wikipedia, "Henderson–Hasselbalch equation" and "Formic acid"; course topic 8.9

Topic 8.10: Buffer capacity 3

  • A buffer is 0.30 M in a weak acid HA and 0.05 M in its conjugate base A⁻. Against which addition does it have the greater capacity? Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; College Board, AP Chemistry Course and Exam Description, essential knowledge 8.10.A.2; course topic 8.10
  • A liter of buffer holds 0.10 mol of acetic acid and 0.10 mol of acetate at pH 4.74. After 0.1 mol of HCl is added, the pH is 2.72. Why did the buffer fail? Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; course topic 8.10
  • Buffer 1 is 0.10 M in acetic acid and 0.10 M in acetate. Buffer 2 is 0.20 M in each. How do the two buffers compare? Purdue University, General Chemistry Topic Review, "Mixtures and Buffers"; course topic 8.10

Topic 8.11: pH and solubility 3

  • Calcium carbonate, CaCO₃, is poorly soluble in pure water and dissolves more as the water becomes acidic. Why? Wikipedia, "Calcium carbonate"; course topic 8.11
  • For which of these sparingly soluble salts would lowering the pH of the solution change the solubility least? College Board, AP Chemistry Course and Exam Description, essential knowledge 8.11.A.1; Wikipedia, "Conjugate (acid-base theory)" and "Hydrofluoric acid"; course topic 8.11
  • Solid magnesium hydroxide is in equilibrium with its ions: Mg(OH)₂(s) ⇌ Mg²⁺(aq) + 2 OH⁻(aq). What happens to its solubility if the pH is raised by adding NaOH? Wikipedia, "Magnesium hydroxide"; course topic 8.11

How this list was compiled: Our own questions, written to Unit 8 (Acids and Bases) of the College Board's AP Chemistry Course and Exam Description, effective fall 2024, https://apcentral.collegeboard.org/media/pdf/ap-chemistry-course-and-exam-description.pdf, read 2026-10-09. Each fact and each constant was read on 2026-10-09 in the public page named under its question: the General Chemistry Topic Review of Purdue University, the PubChem periodic table of the National Library of Medicine, and Wikipedia. Every calculated answer was worked a second time from the numbers in the question. Licence: Own work. Short quotations from the public documents named under each question.

How it works

This AP Chemistry acid-base practice test has 54 questions of our own on Unit 8, Acids and Bases. It is unofficial and not affiliated with or endorsed by the College Board, which owns AP.

Read the full guide

What Unit 8 covers

Unit 8 has eleven topics in the College Board's course description, read October 9, 2026, and each has a set here: introduction to acids and bases (5 questions), strong acids and bases (5), weak acid and base equilibria (8), acid-base reactions and buffers (4), titrations (7), molecular structure (5), pH and pKa (5), properties of buffers (4), the Henderson-Hasselbalch equation (5), buffer capacity (3) and pH and solubility (3). The description gives the topics no weights, so the spread is ours.

Constants and sources

Every Ka, Kb and pKa a question needs is printed in it. The values and rules were read in a Purdue University chemistry review, a Wikipedia article or the PubChem periodic table, named under each answer.

  • Decide what is in the flask before you calculate: a weak acid alone, a buffer, the conjugate base alone, or excess strong base.
  • At the half-equivalence point of a weak acid titration, pH equals pKa.
  • A pH below the pKa means the acid form outnumbers the base form. Above it, the reverse.

Questions and answers

What is Unit 8 in AP Chem?

Acids and Bases, the eighth of nine units: pH, weak acid and base equilibria, buffers and titration curves. The course description allows about 14 to 16 class periods for it.

How much of the AP Chemistry exam is acids and bases?

Between 11 and 15% of the multiple-choice section, by the College Board's course page. Only Unit 3, Properties of Substances and Mixtures, carries more, at 18 to 22%.

Is the Henderson-Hasselbalch equation on the AP Chemistry exam?

Yes. Topic 8.9 uses it for the pH of a buffer, and it is on the equation sheet. The course description says deriving it will not be assessed, and neither will computing the pH change when acid or base is added to a buffer.

Does AP Chemistry cover Lewis acids and bases?

No. The course description says Lewis acid-base concepts are not assessed and keeps the emphasis on reactions in aqueous solution. The questions here use proton donors and acceptors only.

Is this AP Chemistry acids and bases practice test the Unit 8 Progress Check?

No. The Progress Check is the College Board's own question set, assigned by teachers in AP Classroom. The questions here were written for this page, and none repeats or rewords a real one.

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