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Volume I · MMXXVI AP Chemistry
Library› AP Chemistry› Unit 4: Chemical Reactions
⁂   AP Chemistry · Unit 4

4. Chemical Reactions

7–9% of the AP exam. 5 key topics. 4 common errors analyzed.

7–9% exam weight

Unit 4: Chemical Reactions

Unit 4 (Chemical Reactions) is part of the AP Chemistry core curriculum. Work through each key topic in sequence, constructing ICE tables, net ionic equations, or energy diagrams as appropriate.

Key topics in this unit

  1. Physical and chemical changes
  2. Net ionic equations
  3. Stoichiometry and titration
  4. Types of reactions (acid-base, redox, precipitation)
  5. Conservation of mass

Common errors — what the rubric penalizes

These are the most frequently penalized mistakes on AP exam FRQs and MCQs. Review each before your next practice session.

Common error

Writing molecular equations instead of net ionic equations — students include spectator ions, which earns no credit for net ionic equation sub-parts

Common error

Incorrectly assigning oxidation states in redox reactions, especially for elements in polyatomic ions (e.g., S in SO4^2- or Cr in Cr2O7^2-), leading to errors in identifying oxidizing vs. reducing agents

Common error

Stoichiometry errors from using molar ratios from unbalanced equations, or forgetting to convert grams to moles before applying ratios

Common error

Misidentifying reaction type — particularly conflating precipitation with acid-base reactions when both produce a solid or water as a product

Study checklist

  • Can you list all key topics from memory without this page?
  • Have you worked through at least one FRQ-style question per topic?
  • Can you explain each common error above — and why the correct answer differs?
  • Have you reviewed the relevant College Board CED section and formula sheet entries?
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Our worked solutions and practice questions are original instructional content created by Tian2 AP. They are aligned to the concepts and skills described in College Board’s Course and Exam Description and are not reproductions of, or affiliated with, College Board’s official materials.