Analysis of Mistakes and Misconceptions from the 2025 AP Chemistry Exam

Michael Farabaugh | Fri, 08/29/2025 - 11:14

I have been an AP Chemistry Reader since 2011, and I am very grateful for this experience. Not only does the AP Reading give me the chance to connect (and re-connect) with other chemistry teachers from all over the country, but it also provides me the chance to reflect on how I might improve the quality of my instruction and assessments in AP Chemistry.

If you are interested in learning about how to become an AP Reader, I encourage you to check out this information on the AP Central website.

The links shown below will take you to my previous ChemEd X articles about the AP Chemistry Exam.

2022 2023 2024

I will begin with examples of the mistakes or misconceptions that were observed in various student responses from the 2025 AP Chemistry Exam. Then I will offer suggestions for how students and teachers can improve the quality of those responses.

On July 22nd, at the 2025 ChemEd conference in Golden, Colorado, Kyle Beran (Chief Reader for AP Chemistry) and Jamie Benigna (Director of AP Chemistry) presented a session entitled “Summary of Student Successes and Challenges on the 2025 AP Chemistry Exam.”

That presentation will be shared in the form of a webinar, in partnership with the American Association of Chemistry Teachers (AACT). When the details of that webinar are announced on the AACT website, I will add a comment below and share a link so that teachers can register to attend.

I will also add a comment below when the official scoring guidelines and the Chief Reader Report for the 2025 AP Chemistry Exam are available. In the meantime, teachers can check out this section of the AP Central website, which lists free-response questions, scoring guidelines, Chief Reader Reports, and sample student responses (with commentary) from previous years. The seven free-response questions from the operational form of the 2025 AP Chemistry Exam can be found here. My preliminary draft version of the 2025 scoring guidelines can be found here.

Question #1
Part	Mistakes or Misconceptions
A. (i)	Drawing two lines at the same height as the line for Mg-24, so that all three lines show the same percent abundance value of 79% Misinterpreting the scale on the y-axis so that the two lines drawn on the diagram show a percent abundance value of 15% instead of 10.5%.
A. (ii)	Writing incorrect information, such as the following Mg-26 and Mg-25 have a different number of protons (or electrons) Mg-26 has 26 neutrons, and Mg-25 has 25 neutrons
B. (i)	Listing the charge on each ion, but neglecting to make a comparison of the charges of these ions (Na⁺ and Mg²⁺) Neglecting to give an explanation and writing an answer that summarizes the information that had already been stated in the prompt
B. (ii)	Discussing the relative size of the ions, but neglecting to discuss the distance between the ion and the water molecule
C.	Calculating the numerical value of pOH correctly (3.553), but then reporting this value as the final answer, instead of subtracting 3.553 from 14 to get the pH Using the number of moles of OH^– (1.4 × 10^–5 mol) in the pOH calculation instead of using the concentration of OH^–(2.80 × 10^–5 M)
D.	Using the wrong value for volume of Mg(NO₃)_2(aq) Using the wrong value for the total volume of the solution
E. (i)	Including a term for the concentration of the solid Writing [2OH^–]² instead of [OH^–]² Using parentheses (Mg²⁺)(OH^–)² instead of square brackets [Mg²⁺][OH^–]² Omitting the charges on the ions Omitting the exponent of “2” outside [OH^-]
E. (ii)	Using a value for [Mg²⁺] that is different than the value that had been calculated in part D Neglecting to square the value of [OH^–] in the calculation
E. (iii)	Making an incorrect comparison of Q_sp vs. K_sp (which may indicate confusion about comparing two numbers in scientific notation that have a negative exponent) Making the correct comparison of Q_sp vs. K_sp, but then predicting incorrectly that a precipitate would not be formed
F.	Discussing a reaction between H⁺_(aq) and solid Mg(OH)₂ instead of discussing the reaction between the acid and the aqueous OH^– ions Discussing a reaction between H⁺_(aq) and OH^–_(aq), but neglecting to provide an adequate description of how the solubility equilibrium would be affected

Question #2
Part	Mistakes or Misconceptions
A. (i)	Using an incorrect value for the molar mass of H₂O Rounding off the final answer incorrectly
A. (ii)	Using an incorrect value, such as the following 0.16 (instead of 0.32) for the number of moles of H atoms 0.16 (instead of 0.24) for the number of moles of C atoms
B. (i)	Switching the two values for volume (10.0 mL and 16.0 mL) in the setup for the calculation Using the total volume of the two solutions (26.0 mL) in the setup for the calculation instead of using the volume of NaOH (16.0 mL) Incorrectly assuming that HAsc is a strong acid, and then using the initial pH value (2.5) on the titration curve to calculate the value of [HAsc]
B. (ii)	Using a value of approx. 7.5, which represents the pH of the solution at the equivalence point
B. (iii)	Reporting that [Asc^–]/[HAsc] is greater than 1, without doing a calculation Using the wrong mathematical function in the setup (e.g., ln or e^x) Setting up the calculation as 10^–0.6 instead of 10^0.6 Setting up the correct calculation (10^0.6), but neglecting to complete the calculation to get the final answer (4.0)
C. (i)	Writing a vague explanation that omits important details, such as the following which trials are being compared which reactant’s initial concentration is changed which reactant’s initial concentration is held constant
C. (ii)	Making calculation errors Writing the number as “4.55” instead of “4.55 × 10^–4” Omitting the units, or writing incorrect units for k, such as M/s
D.	Referring to dipole-dipole forces instead of ion-dipole forces Discussing attractions between I₃^– ions and H⁺ ions (instead of H₂O molecules) Implying that chemical bonds are formed between I₃^– and H₂O

Question #3
Part	Mistakes or Misconceptions
A.	Using too few electrons or too many electrons to complete the Lewis diagram
B. (i)	Discussing the decrease in the total number of moles and neglecting to mention the states of matter when comparing the reactants and the product Neglecting to use particle-level reasoning (e.g., “solids have less entropy than gases")
B. (ii)	Neglecting to state that a reaction is favored when ΔG° < 0 Discussing ΔH° only without discussing ΔS° Discussing the relationships between ΔG°, ΔH°, and ΔS°, without answering the question regarding the student’s claim Agreeing with the student’s claim, but including contradictory information
C. (i)	Setting up the calculation of q using only the mass of the P₄O₁₀ (0.100 g) instead of using the total mass of the solution (100.1 g) Neglecting to express the final answer with two significant figures (0.16 kJ)
C. (ii)	Using an incorrect value for the molar mass of P₄O₁₀ Using an incorrect setup for the calculation of moles of P₄O₁₀ for the combination of heat (q) and moles of P₄O₁₀ Omitting the negative sign from the value of ΔH
D.	Thinking, incorrectly, that the change in temperature is the result of a warm solid being added to water instead of an exothermic reaction between P₄O_10(s) and H₂O_(l) Neglecting to mention thermal energy (e.g., “less P₄O₁₀ results in less reaction and a smaller ΔT”) Using an inverse relationship between mass and ΔT to support an incorrect prediction that a smaller mass would result in a larger value of ΔT in trial 2
E.	Combining ΔH₁ and ΔH₂ without making a change to the value of ΔH₁ Making errors in the setup for the calculation (¼)((–1148) + (–88)) = –309 kJ (¼)(–1148) – (–88) = –199 kJ
F. (i)	Writing the correct K_p expression, but miscounting the number of particles Misunderstanding the question and assuming that each substance has a partial pressure of 1.00 atm
F. (ii)	Neglecting to mention that an exothermic reaction favors the reactants (or shifts toward the left) when the temperature is increased Misunderstanding Le Châtelier’s principle and the effect of temperature changes on the value of K (e.g., “Heat is a product of an exothermic reaction. As temperature increases, the product increases, so K_p increases.”) Using the relationship between temperature and pressure to justify the prediction (e.g., “When temperature increases, pressure increases, so K_p increases.")

Question #4
Part	Mistakes or Misconceptions
A.	Incorrectly identifying the hybridization as sp³, which may be the result of counting four electron pairs around the C atom instead of counting three electron domains Adding a coefficient (e.g., 3sp²) Instead of the hybridization, providing information related to atomic structure or bonding, such as electron configuration, orbital diagrams, molecular geometry, or the number of sigma and pi bonds
B.	Incorrectly drawing a line that connects the O atom in CH₃OH to one of the H atoms bonded to C in H₂CO the O atom in H₂CO to one of the H atoms bonded to C in CH₃OH two different H atoms two molecules of the same compound Circling a single covalent bond within one molecule Drawing more than one dashed line (In order to earn the point, all lines must be correct)
C. (i)	Giving a single-sided range of values (e.g., “less than 254 K” or “greater than 181 K”) Using vague language that allows for the possibility of a value outside the acceptable range (e.g., “around 181 K”) Incorrectly converting the temperature from K into °C
C. (ii)	Neglecting to show supporting work or the setup for the calculation Using the enthalpy of vaporization for H₂CO (24.2 kJ/mol) instead of the value for CH₃OH (37.6 kJ/mol) Neglecting to show units in the setup for the calculation, which can increase the chances of making algebraic errors, such as the following: (8.59 / 32.04) × (1 / 37.6) = 0.00713 Substituting values given in the question into the equation q = mcΔT

Question #5
Part	Mistakes or Misconceptions
A.	Providing an incorrect term, such as “tetra” or “quadrilateral” Providing an incorrect geometry or using more than one option, such as “tetrahedral pyramidal” or “tetrahedral and bent” Instead of the geometry, providing related information such as the bond angle or the hybridization
B.	Using a justification that only mentions the larger molar mass of compound Y Attributing the relative strengths of the intermolecular attractive forces to dipole-dipole forces or hydrogen bonding attractions Discussing the bond strength instead of London dispersion forces Indicating that boiling a liquid involves breaking bonds
C.	Listing the boiling points of each compound, but neglecting to make a comparison of these values or to connect these values to the relative vapor pressures Mentioning only compound X, but not making a comparison to compound Y Listing the states of matter of each substance at 82°C without explaining why compound X has the higher vapor pressure at 82°C Thinking, incorrectly, that compound Y has the higher vapor pressure because it has the higher boiling point
D.	Writing the ideal gas equation without substituting any values into the equation Setting up the calculation incorrectly, such as n = RT/PV Using the wrong value of the ideal gas constant (8.314 J mol^–1 K^–1) Neglecting to convert the temperature from °C into K

Question #6
Part	Mistakes or Misconceptions
A.	Writing the equation for the reduction half-reaction Al³⁺ + 3 e^– → Al Placing the electrons on the wrong side of the equation Al + 3 e^– → Al³⁺ Neglecting to include the electrons in the equation Al → Al³⁺ Writing the equation for the oxidation half-reaction for zinc Zn → Zn²⁺ + 2 e^–
B.	Neglecting to balance the overall charge in the equation Al + Zn²⁺ → Al³⁺ + Zn Neglecting to cancel out the electrons shown on opposite sides of the equation 2 Al + 3 Zn²⁺ + 6 e^– → 2 Al³⁺ + 3 Zn + 6 e^– Writing the molecular equation instead of the net ionic equation 2 Al + 3 Zn(NO₃)₂ → 2 Al(NO₃)₃ + 3 Zn
C.	Writing a justification that only compares the number of moles of Zn (3) with the number of moles of Al (2) Writing a justification that only compares the molar mass of Zn (65.38 g/mol) with the molar mass of Al (26.98 g/mol) Converting 50.0 grams of Zn and 50.0 grams of Al into moles. Then writing a justification that compares the number of moles of each substance (1.85 mol Al versus 0.765 mol Zn) Incorrectly assuming that the change in mass is only based on the number of electrons lost or gained in the reaction Justifying their choice in terms of the electrode that experiences an increase in mass as the reaction proceeds
D.	Writing the correct answer (2.26 V), but neglecting to show supporting work, and neglecting to identify the half-reactions that were combined Combining the half-reactions for Zn and Au, but using an incorrect set-up to calculate the voltage of the galvanic cell Combining the half-reactions for Zn and Be to produce a voltage of 1.09 V, which is based on the incorrect assumption that Zn must be reduced in the galvanic cell Combining the half-reactions for Au and Be to produce a voltage of 3.35 V, which is based on the mistake of neglecting to include the Zn half-cell

Question #7
Part	Mistakes or Misconceptions
A.	Circling the wrong atom, such as the oxygen atom in the –OH group or one of the hydrogen atoms
B. (i)	Setting up the Kb calculation with incorrect values, such as the following [C₂H₃O₃^–] = 1.3 × 10^–5 M [HC₂H₃O₃] = 2.5 M or 1 M
B. (ii)	Using an incorrect setup, such as the following Ka = 1/Kb Ka = Kw – Kb Ka = 14 – Kb
C.	Neglecting to discuss the details of the given mechanism and providing a general statement, including one of the following the definition of a catalyst a description of how a catalyst affects the activation energy or the reaction rate a general statement that a catalyst does not appear in the overall equation Disagreeing with the claim and identifying H₃O⁺ as either an intermediate or as a spectator ion

Based on these mistakes and misconceptions, the following is a list of suggestions for improving performance on the AP Chemistry exam.

Watch the AP Daily videos that are available on AP Classroom. These videos include essential information on each topic from all nine Units in the AP Chemistry Course and Exam Description. They also include practice questions with helpful tips for how to answer them.
Watch the review videos that are found in the “Review” section of AP Classroom. These videos are led by expert AP Chemistry educators and provide valuable test-taking strategies.
Review the free response questions, scoring guidelines, Chief Reader Reports, and sample student responses from previous years. You can find an archive of previously released free-response questions here. Sample student responses with scoring commentary from previous free-response questions are valuable. When students identify the mistakes made by other students, this may provide valuable lessons and motivation for them to improve the quality of their own responses.
Teachers can utilize a helpful resource created by Nora Walsh entitled “Write This, Not That,” which offers guidance to students as they answer free-response questions. You can click here for more information about how to use this resource.
Teachers are encouraged to train students to be clear and precise when answering questions that involve explanations and justifications. The framework known as Claim, Evidence, Reasoning (CER) can help students to answer these types of questions. Links to articles on CER written by Stephanie O’Brien and Ben Meacham are listed below.
I have created resources for using particle diagrams with acid-base titrations; the links are listed below.
Read each part of each question carefully, and make sure to answer the question completely.
Make a habit of showing the setup for every calculation. Include the correct units in the intermediate steps and in the final answer.
Questions involving net ionic equations and stoichiometry calculations should not be limited to Unit 4. Students should review these concepts during their study of kinetics, thermochemistry, equilibrium, acid-base chemistry, thermodynamics, and electrochemistry.
If a question involves a comparison of the properties of two different substances, include both substances in your response.
Avoid using the word “it” in your response. Vague language makes it difficult for AP Readers to determine the substance to which the student is referring. Identify the specific chemical name or formula of each substance.
Be familiar with the rules for expressing the final calculated value with the correct number of significant figures.
Pay close attention to the given information on each axis on a graph. Teachers can use the “Stimulus Type” filter to search for questions that contain a graph in the Question Bank in AP Classroom.
When referring to Coulomb’s Law in explanations involving interparticle attractive forces, pay attention to the identities of the two species that are involved in the attraction. The “r” used in Coulomb’s law equation listed on the AP Chemistry Equations and Constants Sheet refers to the separation (distance) between the particles. The “r” does not refer to the radius of a single particle.
Pay close attention to the details of your setup for calculations involving the dilution of a solution or calculations related to acid-base titrations.
When studying Le Châtelier’s principle, the common ion effect, and the relationship between pH and solubility, students should understand the following.
- how the value of Q is affected by a particular disturbance to a system at equilibrium
- why the equilibrium position will experience a shift in a particular direction in order to reestablish equilibrium after the disturbance
Practice solving problems with a variety of calculations that are related to acid-base chemistry, including pH, pOH, K_a, K_b, titrations, buffers, the Henderson-Hasselbalch equation, etc.
Practice solving problems that make connections between Topic 1.3 (Elemental Composition of Pure Substances) and Topic 4.5 (Stoichiometry). Teachers can provide practice on how to use a laboratory in order to determine the empirical formula of a compound. One example is FRQ #1 from the 2023 AP Chemistry Free Response Questions.
When providing an explanation for why the sign of ΔS° for a certain process is positive or negative, it is important to use language that describes the behavior of the particles. This usually involves a discussion of the dispersal of matter/energy, the number of possible microstates, arrangements, or degrees of freedom.
Regarding thermodynamic favorability, students should understand the following.
- A negative sign for ΔG° is associated with a thermodynamically favorable process.
- Based on the Gibbs free energy equation (ΔG° = ΔH° – TΔS°), two possible driving forces that support thermodynamic favorability are a negative sign for ΔH° and a positive sign for ΔS°.
Practice with particle diagrams to illustrate the requirements for a substance to behave as a hydrogen bond donor or as a hydrogen bond acceptor.
In questions involving London dispersion forces, students should understand that comparisons of the electron clouds of different substances should include both the core electrons and the valence electrons. For example, the carbon atom has 6 electrons, whereas the silicon atom has 14 electrons.
Regarding vapor pressure and boiling point, it is important for students to understand the following.
- A liquid has a measurable vapor pressure even when the temperature is below the normal boiling point.
- There is an inverse relationship between the vapor pressure of a liquid and its normal boiling point.
- Chemical bonds within molecules are not broken when a pure sample of a molecular substance undergoes evaporation.
Students should explore galvanic cells in order to explore the following.
- the site of oxidation and reduction
- the direction of movement of the electrons through the wire and the ions in the salt bridge
- how the mass of each electrode changes over time
- the process of combining half-reactions to determine the net ionic equation for the overall reaction, and the cell voltage for the overall reaction
- stoichiometric calculations involving the changes in mass for each electrode
Be familiar with the structural features of carboxylic acids and the process of proton transfer for both H⁺ donors and H⁺acceptors.
With respect to Topic 7.7 (Calculating Equilibrium Concentrations), students should practice problems involving each of the following situations.
- Given the value of K, determine the concentrations of all species at equilibrium
- Given the concentrations of all species at equilibrium, determine the value of K
Be able to provide direct evidence from a proposed mechanism to support the claim of a substance being classified as either a catalyst or an intermediate.

I hope this article has been helpful to AP Chemistry teachers as they begin a new school year. Please log in to ChemEd X and add your comments and questions to join the conversation below. I look forward to connecting with you.

Articles by Stephanie O’Brien and Ben Meacham on Claim, Evidence, and Reasoning (CER)

What is Claim, Evidence, and Reasoning?

Implementing the Claim, Evidence, Reasoning Framework in the Chemistry Classroom

Michael Farabaugh’s Activity for Using Particle Diagrams in Acid-Base Titrations

Particle Diagram Matching Activity

Particle Diagram Writing Activity

Video Solutions and Explanations

1. Farabaugh, M., Using Information from the 2022 AP Chemistry Reading to Improve Exam Performance,

August 2022, Chemical Education Xchange.

2. Farabaugh, M., Using Information from the 2023 AP Chemistry Reading to Improve Exam Performance,

August 2023, Chemical Education Xchange.

3. Farabaugh, M., Using Information from the 2024 AP Chemistry Reading to Improve Exam Performance,

August 2024, Chemical Education Xchange.

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AACT Webinar on 09-25-25 at 7PM EST

Thursday, September 25th, 2025 at 7:00 PM EST

Join the AP Chemistry Director, Jamie Benigna, for a detailed analysis of free-response questions from last year’s exam, explaining the rationale behind the questions and the policies for scoring them accurately and fairly. Jamie will share common misconceptions and errors from these responses and make suggestions on how they can lead to improvements in teaching and learning AP Chemistry.

https://american-chemical-society.zoom.com/webinar/register/WN_-qCXcfSIQ...

Scoring Guidelines are now available

If you visit the College Board site for past AP Chemistry Questions ( https://apcentral.collegeboard.org/courses/ap-chemistry/exam/past-exam-q... ), you will notice that the Scoring Guidelines for the 2025 Released FRQs are now available.

https://apcentral.collegeboard.org/media/pdf/ap25-sg-chemistry.pdf

No Chief Reader Report yet, but that document, along with scoring statistics and Sample Responses should be added soon.

Chief Reader Report and Sample Student Responses

If you visit the College Board site for past AP Chemistry Questions ( https://apcentral.collegeboard.org/courses/ap-chemistry/exam/past-exam-q... ), you will see that the 2025 Chief Reader Report is now available, along with Student Sample Responses and Commentary for all seven free-response questions.