If you've spent any time in the trenches of AP Chemistry, you know that not all exams are created equal. Some years are a breeze. Others? They feel like the College Board decided to personally ruin your GPA. The AP Chem FRQ 2015 is widely regarded as one of those "turning point" years. It was the second year of the redesigned curriculum, and frankly, it caught a lot of people off guard.
Most students walk into the exam room expecting the math to be the hard part. It’s chemistry, right? You expect stoichiometry and $PV = nRT$. But 2015 was different. It pushed hard into conceptual understanding, forcing kids to explain why things happened rather than just plugging numbers into a calculator. If you couldn't explain the "why," you were toast.
The Infamous Question 1: Ethanol and Methanol
Question 1 is usually supposed to be a "warm-up," but in 2015, it dove straight into the deep end of intermolecular forces (IMFs). You had to compare ethanol and methanol. On the surface, it seems simple. Both have hydrogen bonding. Both are alcohols.
But then the FRQ asks about the boiling point and the vapor pressure. A lot of students tripped up here because they forgot that while both have H-bonding, the larger carbon chain in ethanol leads to stronger London Dispersion Forces (LDFs). It's a classic trap. You focus so much on the "strong" force that you forget the "weak" ones add up.
The scoring guidelines for the AP Chem FRQ 2015 were brutal on this point. If you didn't mention the polarizability of the electron cloud, you probably lost points. It wasn't enough to say "ethanol is bigger." You had to explain that the larger electron cloud is more polarizable, leading to stronger temporary dipoles. This is the kind of nuance that separates a 3 from a 5.
Photons, Electrons, and Question 2
Then came the spectroscopy. Question 2 moved into the realm of $E = h
u$ and the photoelectric effect.
Honestly, it wasn't the math that killed people here. It was the interpretation of the data. You had to look at a photoelectron spectroscopy (PES) plot and identify the element. For a lot of students in 2015, PES was still relatively "new" in the curriculum.
The question asked about the energy required to remove an electron from the $2s$ versus the $1s$ orbital. If you didn't understand Coulomb's Law, you were guessing. It all comes back to $F = k \frac{q_1q_2}{r^2}$. The closer the electron is to the nucleus (smaller $r$), the stronger the pull. Simple in theory, but under the ticking clock of the AP exam, it feels like rocket science.
The Metal-Air Battery Curveball
One of the more unique parts of the AP Chem FRQ 2015 was the focus on a metal-air battery in Question 3. Electrochemistry is already a headache for most. Add in the concept of a "porous" electrode and oxygen from the air, and you have a recipe for panic.
You had to calculate the mass of $Li$ consumed. It required a solid grasp of the relationship between current ($I = \frac{q}{t}$), Coulombs, and Faradays. If you messed up the unit conversion from $A \cdot h$ (Ampere-hours) to Coulombs, the whole thing collapsed.
Why the 2015 Free Response Questions Felt Different
The 2015 exam marked a shift away from the "plug and chug" era of AP Chem. Before 2014, you could practically memorize the types of problems that would appear. In 2015, the College Board doubled down on the "Science Practices."
- Claim, Evidence, Reasoning (CER): You couldn't just state a fact; you had to back it up with data from the prompt.
- Molecular Modeling: There was a huge emphasis on drawing and interpreting what molecules are doing at the particulate level.
- Laboratory Context: Many questions, like Question 5 regarding the decomposition of $CuCO_3$, were rooted in actual lab procedures.
If you hadn't spent enough time with a buret or a crucible in class, these questions felt abstract. Question 5 specifically asked why a student might get a lower mass of $CuO$ than expected. You had to realize that if the heating wasn't complete, some unreacted $CuCO_3$ would remain. It’s a practical lab error, not a theoretical math problem.
The Equilibrium Trap in Question 4
Question 4 was a short FRQ, but it packed a punch with solubility product constants ($K_{sp}$). It focused on $Ca(OH)_2$.
The "common ion effect" is a favorite topic for the College Board, and it showed up here in full force. When you add $NaOH$ to a saturated solution of $Ca(OH)_2$, the concentration of $OH^-$ increases. According to Le Chatelier’s principle, the equilibrium shifts to the left.
Students often forget that $K_{sp}$ itself doesn't change—only the position of the equilibrium. If you wrote that the "Ksp decreased," the grader marked it wrong immediately. The $K$ value only changes with temperature. It's a fundamental rule, yet it claims victims every single year.
Dealing with the Kinetics of Question 6
By the time students got to Question 6, fatigue was setting in. This question dealt with the reaction between $NO$ and $O_2$. It was a kinetics problem that required identifying the rate law from a mechanism.
Specifically, it involved a "fast equilibrium" step followed by a "slow" rate-determining step. This is the stuff of nightmares for many. You have to substitute the intermediates out of the rate law using the equilibrium expression.
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$rate = k[N_2O_2][O_2]$
But since $[N_2O_2]$ is an intermediate, you have to relate it back to the reactants:
$K = \frac{[N_2O_2]}{[NO]^2} \implies [N_2O_2] = K[NO]^2$
Substitute that back in, and you get the overall rate law. It’s a multi-step mental process that is incredibly easy to fumble when you have five minutes left in the session.
Mastering the AP Chem FRQ 2015 Style
If you are using the AP Chem FRQ 2015 as a practice test, don't just look at the answer key. Look at the "Scoring Statistics." For many of these questions, the average score was below 50%.
That should tell you something.
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The exam isn't designed for you to get every single point. It's designed to see if you can think like a chemist. If you got stuck on the $PV = nRT$ calculation in Question 7 (which involved the pressure of $NO_2$ gas), you weren't alone. That question required a deep understanding of Dalton's Law of Partial Pressures and how stoichiometry applies to gas phases.
Practical Steps for AP Chemistry Success
If you're looking at the 2015 FRQ and feeling overwhelmed, take a breath. It's one of the best diagnostic tools you have because it covers so much ground. Here is how to actually use it to improve your score:
Analyze the Verbs
Go through the 2015 FRQ and circle the command verbs. "Calculate" is easy. "Justify" and "Explain" are where the points are lost. For every "Justify" answer, ensure you've linked a macroscopic observation (like a boiling point) to a microscopic cause (like IMFs).
Redo the Math Without a Calculator (Sort of)
While you get a calculator on the FRQs now, the 2015 exam had some "long" questions and some "short" ones. Practice doing the mental math for things like $pH$ or molar mass. It builds "number sense" so you can spot an unreasonable answer before you write it down.
Focus on the Particulate Level
The 2015 exam loved asking students to visualize atoms. Get comfortable drawing "beaker diagrams." If you're asked to draw a solution of $MgCl_2$, make sure you have twice as many $Cl^-$ ions as $Mg^{2+}$ ions. It sounds pedantic, but it’s exactly what the 2015 graders were looking for.
Review the Chief Reader Report
This is a goldmine. The Chief Reader for AP Chemistry releases a report every year detailing where students messed up. For 2015, they noted that many students struggled with the concept of "force" vs "energy" and frequently used terms like "hydrogen bonds" when they meant "covalent bonds." Avoid these vocabulary slips.
The AP Chem FRQ 2015 remains a staple of AP prep because it perfectly encapsulates the "New AP" philosophy. It’s less about memorizing the solubility rules and more about understanding why certain ions stay apart while others clump together. If you can master the logic of the 2015 exam, the modern exams will feel much more manageable.
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Go back to Question 3. Try to work through the battery problem again. If you can handle the unit conversions and the redox logic there, you're in a great spot for whatever the College Board throws at you this year.