• 51 questions

AP Chemistry Unit 4 Practice Test

Unofficial multiple-choice practice for Unit 4 of AP Chemistry, Chemical Reactions: net ionic equations, stoichiometry, titration and redox.

Table sugar is stirred into water until it dissolves. Later the water is left to evaporate and the same sugar is recovered. What kind of change was the dissolving?

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.

Next step Next: AP Chemistry acid-base practice testAP Chemistry Unit 1: atomic structure

All 51 questions

Topic 4.1: Introduction for reactions 4

  • A chip of calcium carbonate is dropped into hydrochloric acid at room temperature. Bubbles of gas stream off and the chip slowly disappears. What do the bubbles show? Wikipedia, "Calcium carbonate" and "Physical change"; course topic 4.1
  • A student heats a beaker of pure water and sees bubbles of gas rise from the bottom. Why is this weak evidence of a chemical change? Wikipedia, "Physical change"; course topic 4.1
  • In which of these cases has a new substance formed? Wikipedia, "Physical change" and "Half-reaction"; course topic 4.1
  • Table sugar is stirred into water until it dissolves. Later the water is left to evaporate and the same sugar is recovered. What kind of change was the dissolving? Wikipedia, "Physical change"; course topic 4.1
Show all 51 questions (47 more)

Topic 4.2: Net ionic equations 5

  • Aluminum metal reacts with oxygen gas to form Al₂O₃. In the balanced equation with the smallest whole numbers, how many aluminum atoms react with three O₂ molecules? Purdue University, General Chemistry Topic Review, "Chemical Reactions"; PubChem periodic table, National Library of Medicine; course topic 4.2
  • Aqueous silver nitrate and aqueous sodium chloride react: AgNO₃ + NaCl → AgCl(s) + NaNO₃. What is the net ionic equation? Wikipedia, "Spectator ion" and "Silver chloride"; course topic 4.2
  • In the reaction HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l), which ions are spectator ions? Wikipedia, "Spectator ion" and "Neutralization (chemistry)"; course topic 4.2
  • What must be equal on the two sides of a correctly balanced net ionic equation? Purdue University, General Chemistry Topic Review, "Chemical Reactions"; Wikipedia, "Oxidation state"; course topic 4.2
  • Which equation represents a physical change? Wikipedia, "Phase transition"; Purdue University, General Chemistry Topic Review, "Chemical Reactions"; course topic 4.2

Topic 4.3: Representations of reactions 4

  • A particle diagram shows 4 H₂ molecules and 4 O₂ molecules. They react as far as possible: 2 H₂ + O₂ → 2 H₂O. What does the diagram show afterward? Purdue University, General Chemistry Topic Review, "Chemical Reactions"; course topic 4.3
  • A particle diagram shows 6 H₂ molecules and 3 O₂ molecules in a sealed box. They react completely: 2 H₂ + O₂ → 2 H₂O. What should the diagram of the box show afterward? Purdue University, General Chemistry Topic Review, "Chemical Reactions"; course topic 4.3
  • A student draws particle diagrams of a closed container before and after a reaction. Which count must be the same in both diagrams? Purdue University, General Chemistry Topic Review, "Chemical Reactions"; course topic 4.3
  • Which particle diagram best represents a dilute solution of sodium chloride in water? Wikipedia, "Salt (chemistry)"; course topic 4.3

Topic 4.4: Physical and chemical changes 4

  • Boiling a sample of water takes much less energy than breaking the same water into hydrogen and oxygen. What explains the difference? Wikipedia, "Intermolecular force"; course topic 4.4
  • Dissolving sodium chloride in water can reasonably be called a physical or a chemical process. Which description of the particles supports both views? Wikipedia, "Salt (chemistry)" and "Solvation"; course topic 4.4
  • When liquid water boils, which attractions are overcome? Wikipedia, "Intermolecular force" and "Phase transition"; course topic 4.4
  • Which process breaks and forms covalent bonds? Wikipedia, "Chemical reaction"; Purdue University, General Chemistry Topic Review, "Chemical Reactions"; course topic 4.4

Topic 4.5: Stoichiometry 9

  • A thermite mixture holds 1.0 mol of Al and 1.0 mol of Fe₂O₃. The reaction is 2 Al + Fe₂O₃ → Al₂O₃ + 2 Fe. Which reactant runs out first, and how much iron forms? Wikipedia, "Stoichiometry"; Purdue University, General Chemistry Topic Review, "Chemical Reactions"; course topic 4.5
  • A vessel holds 4.0 mol of H₂ and 1.0 mol of O₂. They react as far as possible: 2 H₂ + O₂ → 2 H₂O. How much hydrogen is left over? Purdue University, General Chemistry Topic Review, "Chemical Reactions"; Wikipedia, "Stoichiometry"; course topic 4.5
  • Calcium carbonate reacts with acid: CaCO₃(s) + 2 HCl(aq) → CaCl₂(aq) + CO₂(g) + H₂O(l). What volume of CO₂ at 298 K and 1.00 atm forms from 5.00 g of CaCO₃ (100.09 g/mol) and excess HCl? (R = 0.08206 L·atm/(mol·K)) Purdue University, General Chemistry Topic Review, "Solutions"; Wikipedia, "Stoichiometry"; course topic 4.5
  • Excess sodium chloride is added to 50.0 mL of 0.200 M AgNO₃: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq). What mass of AgCl (143.32 g/mol) precipitates? Purdue University, General Chemistry Topic Review, "Solutions"; Wikipedia, "Silver chloride"; PubChem periodic table, National Library of Medicine; course topic 4.5
  • For 2 H₂ + O₂ → 2 H₂O, which statement about the reacting amounts is correct? Purdue University, General Chemistry Topic Review, "Chemical Reactions"; course topic 4.5
  • Hydrogen and oxygen react by 2 H₂ + O₂ → 2 H₂O with oxygen in large excess. If the amount of hydrogen is doubled, what happens to the greatest amount of water that can form? Purdue University, General Chemistry Topic Review, "Chemical Reactions"; Wikipedia, "Stoichiometry"; course topic 4.5
  • In the thermite reaction, 2 Al(s) + Fe₂O₃(s) → Al₂O₃(s) + 2 Fe(l). How many moles of Fe₂O₃ react completely with 0.60 mol of aluminum? Purdue University, General Chemistry Topic Review, "Chemical Reactions"; course topic 4.5
  • Magnesium burns in oxygen: 2 Mg(s) + O₂(g) → 2 MgO(s). What mass of MgO (40.30 g/mol) forms when 6.08 g of Mg (24.31 g/mol) burns in excess oxygen? Purdue University, General Chemistry Topic Review, "Chemical Reactions"; PubChem periodic table, National Library of Medicine; course topic 4.5
  • Propane burns: C₃H₈(g) + 5 O₂(g) → 3 CO₂(g) + 4 H₂O(g). What mass of O₂ (32.00 g/mol) is needed to burn 11.0 g of propane (44.10 g/mol)? Purdue University, General Chemistry Topic Review, "Chemical Reactions"; PubChem periodic table, National Library of Medicine; course topic 4.5

Topic 4.6: Introduction to titration 6

  • A 25.0 mL sample of hydrochloric acid is titrated with 0.100 M NaOH: HCl + NaOH → NaCl + H₂O. The equivalence point comes at 20.0 mL of NaOH. What is the concentration of the acid? Purdue University, General Chemistry Topic Review, "Solutions"; Wikipedia, "Neutralization (chemistry)"; course topic 4.6
  • A student titrating an acid with NaOH adds base well past the color change before reading the buret. How does this affect the acid concentration the student calculates? Purdue University, General Chemistry Topic Review, "Solutions"; course topic 4.6
  • A titration of 10.0 mL of HCl needs 30.0 mL of NaOH to reach the equivalence point. The two react 1 to 1. How do the two concentrations compare? Purdue University, General Chemistry Topic Review, "Solutions"; Wikipedia, "Neutralization (chemistry)"; course topic 4.6
  • In a titration, what is the difference between the equivalence point and the endpoint? Purdue University, General Chemistry Topic Review, "Solutions"; course topic 4.6
  • In a titration, what is the titrant? Wikipedia, "Titration"; course topic 4.6
  • Oxalic acid gives up two protons to base: H₂C₂O₄(aq) + 2 NaOH(aq) → 2 Na⁺(aq) + C₂O₄²⁻(aq) + 2 H₂O(l). How many moles of NaOH are needed to reach the equivalence point with 0.0150 mol of oxalic acid? Purdue University, General Chemistry Topic Review, "Solutions"; course topic 4.6

Topic 4.7: Types of chemical reactions 9

  • In any oxidation-reduction reaction, which way do electrons move? Wikipedia, "Redox"; course topic 4.7
  • Methane burns: CH₄ + 2 O₂ → CO₂ + 2 H₂O. What happens to the carbon atom? Purdue University, General Chemistry Topic Review, "Oxidation-Reduction Reactions" and "Oxidation Numbers"; course topic 4.7
  • Sodium reacts with chlorine: 2 Na + Cl₂ → 2 NaCl. How does the oxidation number of chlorine change? Purdue University, General Chemistry Topic Review, "Oxidation Numbers"; Wikipedia, "Redox"; course topic 4.7
  • Solutions of silver nitrate and sodium chloride are mixed, and a white solid settles out. What is the solid? Wikipedia, "Silver chloride"; College Board, AP Chemistry Course and Exam Description, essential knowledge 4.7.A.5; course topic 4.7
  • Solutions of sodium nitrate and potassium chloride are mixed. Why does no precipitate form? College Board, AP Chemistry Course and Exam Description, essential knowledge 4.7.A.5; Wikipedia, "Chemical reaction"; course topic 4.7
  • What are the products of the complete combustion of ethane, C₂H₆? Wikipedia, "Combustion"; course topic 4.7
  • What is the oxidation number of chlorine in the perchlorate ion, ClO₄⁻? Purdue University, General Chemistry Topic Review, "Oxidation Numbers"; PubChem periodic table, National Library of Medicine; course topic 4.7
  • Which equation shows an acid-base reaction? Purdue University, General Chemistry Topic Review, "Acids and Bases"; Wikipedia, "Neutralization (chemistry)"; course topic 4.7
  • Zinc metal goes into a solution of copper(II) sulfate and copper metal is deposited: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s). What type of reaction is this? Wikipedia, "Redox"; course topic 4.7

Topic 4.8: Introduction to acid-base reactions 5

  • Hydrochloric acid is a strong acid. What does that tell you about its conjugate base, the chloride ion? Wikipedia, "Conjugate (acid-base theory)"; course topic 4.8
  • Hydrogen chloride dissolves in water: HCl + H₂O → H₃O⁺ + Cl⁻. What does the water molecule do in this reaction? Purdue University, General Chemistry Topic Review, "Acids and Bases"; course topic 4.8
  • In the reaction CH₃COOH + H₂O ⇌ CH₃COO⁻ + H₃O⁺, which two species act as acids, one in each direction? Wikipedia, "Brønsted–Lowry acid–base theory"; course topic 4.8
  • Water acts as a base toward HCl and as an acid toward NH₃. What property of water does this show? Wikipedia, "Brønsted–Lowry acid–base theory"; course topic 4.8
  • Which pair is a conjugate acid-base pair? Wikipedia, "Conjugate (acid-base theory)"; course topic 4.8

Topic 4.9: Oxidation-reduction (redox) reactions 5

  • Aluminum metal reacts with copper(II) ions: 2 Al + 3 Cu²⁺ → 2 Al³⁺ + 3 Cu. How many electrons are transferred when the reaction happens once as written? Wikipedia, "Chemical reaction"; PubChem periodic table, National Library of Medicine; course topic 4.9
  • Hydrogen and fluorine react: H₂ + F₂ → 2 HF. Which is the reduction half-reaction? Wikipedia, "Redox"; course topic 4.9
  • In the reaction Zn + Cu²⁺ → Zn²⁺ + Cu, which is the oxidation half-reaction? Wikipedia, "Redox"; course topic 4.9
  • Two half-reactions are to be combined: Fe³⁺ + e⁻ → Fe²⁺ and Sn²⁺ → Sn⁴⁺ + 2 e⁻. How many Fe³⁺ ions react for each Sn²⁺ ion? Wikipedia, "Chemical reaction"; course topic 4.9
  • Which equation for the reaction of copper metal with silver ions is balanced for both atoms and charge? Wikipedia, "Chemical reaction" and "Oxidation state"; PubChem periodic table, National Library of Medicine; course topic 4.9

How this list was compiled: Our own questions, written to Unit 4 (Chemical Reactions) 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 balanced equation 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 Unit 4 practice test has 51 questions of our own on Chemical Reactions, from net ionic equations to redox. It is unofficial and not affiliated with or endorsed by the College Board, which owns AP.

Read the full guide

What Unit 4 covers

Unit 4 has nine topics in the College Board's course description, read October 9, 2026, and each has a set here: introduction for reactions (4 questions), net ionic equations (5), representations of reactions (4), physical and chemical changes (4), stoichiometry (9), introduction to titration (6), types of chemical reactions (9), introduction to acid-base reactions (5) and redox reactions (5). The description gives the topics no weights, so the spread is ours.

Sources you can open

Each balanced equation and rule was read in the page named under its answer: a Purdue University chemistry review or a Wikipedia article. Molar masses come from the PubChem periodic table and are printed in the questions.

  • Convert to moles before any stoichiometry step. Coefficients compare moles, never grams.
  • The exam does not test the terms oxidizing agent and reducing agent. Say which species is oxidized and which is reduced.
  • In a redox equation check charge as well as atoms: electrons lost must equal electrons gained.

Questions and answers

What is Unit 4 in AP Chem?

Chemical Reactions, the fourth of nine units: how to write, balance and classify reactions and how to calculate with them. The course description allows about 14 to 15 class periods for it.

How much of the AP Chemistry exam is Unit 4?

Between 7 and 9% of the multiple-choice section, by the College Board's course page. Its titration and acid-base topics return in Unit 8, Acids and Bases, which carries 11 to 15%.

Do I need to memorize solubility rules for AP Chemistry?

Only one. The course description says every sodium, potassium, ammonium and nitrate salt dissolves in water, and that rote memorization of other solubility rules will not be assessed. A question here gives or implies anything else you need.

Can you use a calculator on the AP Chemistry exam?

Yes. The College Board's exam page says calculators are permitted, and the course description recommends a scientific or graphing calculator for both sections. Have one beside you for the stoichiometry set.

Are these real AP Chemistry Unit 4 questions?

No. The College Board owns the real exam questions and the Unit 4 Progress Check, and nothing here copies or rewords them. These questions were written for this page from the unit's topic list.

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