The Library of Competitions
Tian2 Editions
A three-part National exam — Part I 60-MCQ, Part II eight problems, Part III a real wet lab — preceded by a Local 60-MCQ qualifier. Twelve official PDFs normalized in the Tian2 archive. Two reader-facing editions published.
The USNCO is unusual in this library because of its lab component. Most olympiads end at the written paper. USNCO's National exam includes Part III — a real, ninety-minute, supplied-equipment wet lab — that no amount of textbook study can replace. A student preparing for the National exam needs lab time as well as theory time, which makes USNCO advancement strongly dependent on school chemistry-lab access.
The pathway begins with a Local Exam in early spring — a 60-question MCQ in 110 minutes, administered by ACS local sections. Top scorers are invited to the National Exam in April, which runs the three parts across a single day. The top twenty students attend the two-week Study Camp at the University of Maryland, College Park, in late May into June; four are selected for the International Chemistry Olympiad in July. Confirm this year's exact dates against the official ACS page.
12 Tier-1 PDFs fetched and normalized: 2022 Local; 2023 National I/II/III; 2024 Local + National I/II/III; 2025 Local + National I/II/III. 8,115 normalized text lines across 203 pages. Tier-1 ACS HTML pages remain Incapsula-blocked (5 URLs) — eligibility, registration, and award-tier details must be verified against the official ACS site.
| Part | Format | Time | What it tests |
|---|---|---|---|
| Local Exam | 60 MC (A–D) | 110 min | Breadth across general chemistry; calculator allowed. |
| National Part I | 60 MC (Gradescope sheet) | 90 min | Same MCQ form, harder questions, tighter pace. |
| National Part II | 8 long problems (printed % weights) | 105 min | Show all working. Multi-step derivations. Written net equations and Lewis structures. |
| National Part III | 2 lab tasks (any order) | 90 min | Real wet lab; supplied equipment; safety sign-off required; one chemical replacement allowed. |
From a systematic keyword scan across all 12 normalized booklets, these chemistry domains appear consistently across Local and Part I papers:
| Domain | Key concepts to master |
|---|---|
| Stoichiometry & analytical | Aqueous concentration, gravimetric/mass-loss, buret reading, glassware-precision selection |
| Thermochemistry | Calorimetry, Hess's law, ΔE vs ΔH, latent heat, bond-dissociation energy |
| Phase & solid state | Phase diagrams, intermolecular forces (HF/HCl/HBr/HI), allotropes, FCC unit cell/density |
| Kinetics | Rate laws from stoichiometry, Arrhenius, mechanism → rate law, pseudo-order, heterogeneous catalysis |
| Equilibrium & solubility | Ksp, heterogeneous equilibria, salts of weak acids/bases, NH4F-type pH, weak-base hydrolysis |
| Acid–base | Titration-curve identification, pH of polyprotic and salt solutions |
| Electrochemistry | Nernst equation, standard reduction potentials, oxidant/reductant identification |
| Nuclear | Half-life calculations, electron capture, radioactive decay |
| Organic / structure | Isomerism, H-bonding/solubility prediction, Lewis structures with formal charges |
Part II uniquely carries printed per-problem weights ([10%]–[14%] per problem in 2024) and multi-domain questions. Part III stands apart: two lab problems with a literal “Question:” line, safety language, and an examiner script in the same PDF.
Stage 1 — Local MCQ at pace. Drill 60-MC sets at ~110 s/question (2022, 2024, 2025 Local booklets). Build keyword-lexicon fluency and calculator discipline.
Stage 2 — National Part I speed. Move to 90 s/question (2023, 2024, 2025 Part I). Wider topic spread: complex-ion equilibria, Clausius–Clapeyron, SN2-shaped kinetics.
Stage 3 — Part II written reasoning. Budget 13 min/problem. Practice writing net equations, full Lewis structures with formal charges, and justified qualitative answers. Use the printed [N%] weights to allocate time per sub-part.
Stage 4 — Part III lab readiness. Rehearse: design procedure → safety sign-off → execute → record. Practise under the one-replacement allowance and 90-minute clock. Lab time in a real school lab is not optional.
Five ACS HTML pages — eligibility, registration, award tiers, study-camp invitation logic, and the 2026 calendar — are behind Incapsula JS-challenge protection. These surfaces are documented as standing boundaries in our source ledger. The published editions are explicitly structured to work from the 12 verified PDFs and to redirect all program-rules questions to the official ACS pages or to a student's local-section contact.
You can't fake the lab in Part III. Find a school chemistry teacher who'll let you titrate.— Editor's note
Exam-structure tables verified from booklet directions. Four-stage drill plan (Local → Part I → Part II → Part III). Topic-vocabulary scaffold. Local-section logistics for five sampled sections. Exam-day checklist. 9 pages.
Supervision frame: pacing budgets, booklet-rotation schedule, five-section logistics table with teacher checklist, month-by-month calendar template, 11-item risk register, Q&A redirect protocol, Part III exam-day proctor script. 10 pages.
Unofficial; not affiliated with or endorsed by the American Chemical Society. Original exam questions remain © ACS. These editions are original analysis derived from the publicly available past-exam PDFs — they do not reproduce ACS question text.
The USNCO is the United States' sole official pathway to the International Chemistry Olympiad, which has been held annually since 1968. The US has participated since 1984 and has consistently ranked among the top national delegations — a track record that reflects both the depth of the Local-exam network (run by ACS local sections in most major cities) and the intensity of the two-week Study Camp at the University of Maryland.
For a student whose aim is simply the National exam — rather than IChO selection — the USNCO is still one of the most content-rich chemistry competitions available in the US. National Part II is a genuine long-form derivation paper; Part III is a real wet lab. The combination makes USNCO preparation unusually transferable to college-level chemistry coursework.
Registration for the Local Exam goes through your ACS local section, not through ACS headquarters directly. The five local sections sampled in our logistics memo (NY ACS, Southern Arizona ACS, Cleveland ACS, North Carolina ACS, SCALACS) all had distinct deadlines and registration forms for the 2026 cycle — the earliest closed in late January. Find your local section via the ACS section locator and check their specific calendar, not the ACS national page alone.
