How to study for the USNCO Chemistry Olympiads

Originally posted 2025-08-29

Obligatory disclaimer: all opinions are mine and not of my employer

In 2006 and 2007, I competed in the USNCO, making it to the Study Camp in 2006 (my junior year in high school) and then to the IChO in 2007, winning a silver medal in Moscow, Russia. Afterwards, I majored in Chemistry at MIT and mentored students at the Study Camp from 2010-2012. In 2013-15, I wrote the majority of the ChemWOOT course, which I credit for the massive difficulty bump that happened in 2017 at the USNCO National level.

Here’s my take on preparing for the USNCO.

What is the USNCO?

The US National Chemistry Olympiad (USNCO) is a three-tier competition run by the American Chemical Society (ACS) to select the top high school students (4, plus alternates) to represent the United States at the International Chemistry Olympiad (IChO).

The first tier is the Local examination, which is a 60-question multiple choice exam. Anybody is eligible to compete, and 10-20,000 students take the Local exams each year in March.

The second tier is the National examination, which has three parts: a harder 60-question multiple choice section, an 8-question free response section, and a hands-on experimental lab section. The top ~1000 students across the U.S. are invited to take this exam, occuring late April.

The third tier is the USNCO Study Camp, a two-week intensive where students spend all day learning advanced chemistry, running lab experiments, and taking theoretical exams as difficult as the ones at the IChO. The top-scoring 20 students from the National level are invited to this camp, occuring in June.

The IChO is hosted by a different country every year and occurs in July.

How hard is the USNCO?

USNCO locals are roughly the level of the AP Chemistry test - if you can get a 5 on the AP, you’ll do decently on this test. However, to make the cut for nationals, you’ll need to score near-perfectly, especially in competitive states like California.

Qualifying for the National level is a big accomplishment, placing you in the top 1,000 out of approximately 10-20,000 students who take the USNCO Local examination.

USNCO Nationals are at the level of a typical college introductory course in General Chemistry. On top of the standard AP Chemistry topics, the USNCO Nationals will expect you to be able to handle elaborate calculations:

equilibrium: multiprotic acids/bases, buffers, zwitterions, complexation, common-ion, solubility with interfering ions
kinetics: rate laws, pre-equilibrium approximation, steady-state approximation, Michaelis-Menten equation, catalysts, Arrhenius rate equation, and connection with equilibrium (e.g. Curtin-Hammett principle)
thermodynamics: a thorough understanding of Delta G, Delta S, Delta H, and non-equilibrium conditions
electrochemistry: batteries, reduction potential, and calculation of potentials at non-standard conditions
“trivia”: flame test colors, advanced solubility rules, transition metal ion colors, properties of unusual ions with niche uses (cyanide, superoxides, carbides, peroxides, thiocyanates, azides, thiosulfate, triiodide, fulminates).
organic chemistry: knowledge roughly equivalent to an introductory class at the college level.

The Study Camp and IChO test your chemistry understanding at a level comparable to a college junior majoring in Chemistry.

Compared to the other olympiads, the USNCO is more difficult than the USABO (biology) exam, but less difficult than the USAPhO (Physics) exam. The USAMO is by far the most difficult exam of the group.

Why compete in the USNCO?

There are a variety of reasons, both short-term and long-term, that I think it’s a good idea to compete in the USNCO (and really, any high school math/science olympiad).

The crass: Qualifying for the Study Camp is a tremendous accomplishment, and a ticket to most Ivy+ colleges. The ACS also publishes a runner-up list of the next 50/150 students at the National level - also strong signals for your college application.

The motivational: If you / your kid is talented and driven by recognition, then it’ll be inevitable that they will saturate their school’s ability to recognize and encourage their continued growth. My personal take is that you are growing at your optimal rate when you are at the ~75th percentile of your peer group. For the top 10% of students, this means that you need to find a regional/state/national level of competition to continue fostering growth.

The environmental: To understand issues on sustainability and climate change, you need something beyond what AP Chemistry or arguably even a college General Chemistry course can provide. I see people misunderstand basic chemical issues all the time, even from people who are otherwise well-educated. Preparing for the USNCO Nationals puts you at a level that I consider “good enough” to actually understand chemistry issues.

The foxy: (“Fox”, as in the idiom “a fox knows many things, but a hedgehog knows one big thing) The chemistry “rules” you learn at the AP chemistry level are misleadingly simple – real chemistry is a volatile mix of heuristics and modeling approaches. You must learn to think from multiple angles, to weigh competing models, and decide which is the right approach. The AP Chemistry curriculum does not teach at a rigorous enough level to achieve this effect. For parents: I think this is the strongest reason to encourage your kid(s) to try the Chemistry olympiad in particular over the other subjects.

The multitasking: At the national/international level, the lab tasks involve an impressive level of multitasking. Chemical reactions take time to finish, and the lab exams are always set so that you must always be interleaving the preparation of one reaction with the waiting on another reaction’s completion.

Strategies for Studying

To score well on the USNCO (local or national level), you’ll want to know your material, and additionally, be able to apply it rapidly and accurately under timed conditions. This implies a level of deliberate practice that most students shy away from.

Step 1 is to practice the real thing by taking old exams under realistic timed conditions. The ACS makes past years’ exams available for free online - you can print out and take these exams with pen and paper.

Step 2 is to review your results after taking the exam. Consider the following questions: Did I get lucky? Am I missing a fundamental skill? Did I have to spend several minutes remembering how to do a certain calculation? Even if I didn’t know something, were there clever ways I could have eliminated options and guessed at the final answer?

Step 3 is to fill in your knowledge gaps, and then systematically practice problems in that area until the calculations are drilled into your brain.

Finally, take another practice exam to see how you’ve improved - rinse and repeat!

On the day of the test, the standard advice applies: get a good night’s sleep, spend all the alloted time, carefully review each problem, and don’t panic.

I have built my USNCO prep site, Cartesian Tutor with this approach in mind. Please give it a try: it lets you take practice exams under timed conditions, to get AI hints and grading on your work, and to get 1:1 AI tutoring on the difficult concepts appearing in the USNCO.

Timelines for studying

Because the USNCO Locals and National exams happen back-to-back in March and April, there is very little time to study in between the two exams. On top of that, you may not get your exam results back immediately, meaning that you may have just a few short weeks in between learning that you’ve qualified for the National exam and actually taking the National exam.

The USNCO Local and National multiple choice exams are identical in format and topic coverage, differing only in difficulty, so it’s a no-brainer to study for both of these at the same time throughout the school year. The multiple choice section is the exam to prepare for if you’re doing the USNCO for the first time.

On a tactical note - the ACS uses the multiple-choice section to winnow down to 150 students to save the effort of grading everybody’s free response answers - so for now, it’s actually possible to make the top 150 list with a blank free response section. (Caveat emptor: the increasing availability of AI grading may make it feasible to do a rough first pass on Free Response grading next year, obsoleting this tactic!) To qualify for the top 50 or top 20, you’ll also have to do well on the Free Response section.

You’ll want to switch to studying for the Free Response section relatively early on – perhaps in November or December – while occasionally continuing to take practice Multiple Choice sections to keep that muscle memory fresh.

Advanced study

By the time you’ve done all the past USNCOs, you’re probably in contention for the top 20 Study Camp invitees. At this point, I would recommend Clayden’s Organic Chemistry textbook, and working through IChOs and preparatory problems. The Prep Problems are a set of longer-form questions, not intended to be taken in test conditions, but instead as a teaching aid and teaser for the specific problems that will appear on that year’s IChO. Not all countries are equal; some years’ prep problems and IChOs are drastically easier than others. If in doubt, Soviet-bloc countries and East Asian countries tend to run on the harder side, and Russia’s tests are the hardest by far. My friend Anugrah compiled some notes on the relative difficulty levels of past IChOs that you may find useful. I intend to add some flavor of this difficulty annotation to Cartesian Tutor

The best tool for studying for the USNCO

Cartesian Tutor is my implementation of these best practices for studying for the USNCO. It’s under active development, but features should roll out in time for anyone preparing for the 2026 USNCOs.

I’ll be building AI features that enable you to get carefully calibrated hints, interactive lessons on advanced topics, and instant feedback on your solutions, as well as non-AI features like difficulty ratings, progress tracking and time management.