AP Chem · Unit 4 Progress Check

AP Chemistry Unit 4 Progress Check Chemical Reactions walkthrough.

AP Chemistry Unit 4 is chemical reactions, and the Unit 4 Progress Check MCQ leans on stoichiometry, reaction types, and net ionic equations. This walkthrough covers what each question type tests, the traps, and how to work through them. Explanations only — no AP Classroom answer keys.

Updated August 2026Written by Mahmudul HasanFree · No signup

What Unit 4 covers

Unit 4 is Chemical Reactions. Chemical reactions is roughly 7–9% of the AP Chemistry exam and a prerequisite for kinetics and equilibrium.

Reaction types

Synthesis, decomposition, single and double replacement, combustion, and acid-base.

Net ionic equations

Writing them by removing spectator ions from the complete ionic equation.

Stoichiometry

Mole ratios, limiting reactant, and percent yield.

Solution stoichiometry

Molarity, dilution, and reactions in solution.

Oxidation-reduction

Assigning oxidation numbers and identifying what is oxidised and reduced.

Titrations

Using stoichiometry to find an unknown concentration.

The Progress Check MCQ: what each question type tests

These are the question patterns that recur on this Progress Check, and what each one is really asking.

Identify the limiting reactant

Convert both reactants to product and compare — the one that yields less is limiting.

Write a net ionic equation

Cancel spectator ions. Only the species that actually change belong in the final equation.

Predict the products

Reaction type tells you the products — recognise the pattern first.

Redox identification

Oxidation is a loss of electrons and an increase in oxidation number; reduction is the reverse.

Solution calculation

Use moles = molarity times volume, and track dilution with M1V1 = M2V2.

The Progress Check FRQ

Unit 4 free response often asks for a net ionic equation and a stoichiometric calculation. Points come from a correctly balanced equation with only the reacting species, identifying the limiting reactant with work shown, and carrying units through the mole conversions.

Where students lose the most points

Leaving spectator ions in a net ionic equation

Ions that appear unchanged on both sides are removed entirely.

Assuming equal moles means complete reaction

Check the mole ratio — stoichiometry, not raw amounts, sets the limiting reactant.

Forgetting to balance charge and mass

Net ionic equations must balance both.

Confusing oxidation and reduction

Loss of electrons is oxidation; a rise in oxidation number signals it.

Skipping the mole ratio

Grams to grams always goes through moles.

How to work through this unit

For any reaction quantity question, work in moles from start to finish and let the balanced equation’s ratio do the work. Most Unit 4 errors are ratio errors, not arithmetic.

Once you have finished the Progress Check, put your raw score into our AP Chemistry Calculator to see roughly where that pace puts you on the 1–5 scale, and use the AP Chemistry Review for the full exam format and study plan.

Frequently asked questions

Quick answers — written by humans, not a chatbot.

What does the AP Chemistry Unit 4 Progress Check cover?

Chemical reactions: reaction types, net ionic equations, stoichiometry and limiting reactants, solution stoichiometry, oxidation-reduction, and titrations.

How do I write a net ionic equation?

Write the balanced complete ionic equation, then cancel the spectator ions that appear unchanged on both sides. Only the species that actually react remain.

How do I find the limiting reactant?

Convert the amount of each reactant to the amount of product it could form using the mole ratio, and the reactant that produces the least product is limiting.

Do you publish AP Chemistry Unit 4 answer keys?

No. We publish walkthroughs of the reasoning and the traps rather than raw AP Classroom answers.