ACS Chemistry Olympiad

Grades

9-12 (typically; some ACS Local Sections allow advanced 7th-8th graders for Local Exam)

Age

Must be under 20 years old on July 1 of the competition year

Citizenship

For Local and National Exams: No citizenship requirement. For Study Camp and IChO team: Must be U.S. citizen or permanent resident (green card holder)

Prerequisites

Solid foundation in high school chemistry (AP Chemistry or Honors Chemistry equivalent recommended for competitive standing)

Steps

1. Stage 1 (Local Exam - March): Register through your school's chemistry teacher or contact your ACS Local Section directly. Exam administered at your school or local proctored site
2. Stage 2 (National Exam - Mid-April): Top performers from each Local Section (typically ~12 per section, capped at 2 per high school) automatically nominated; no separate application needed
3. Stage 3 (Study Camp - Early June): Top 20 students nationally invited automatically; no application required
4. Stage 4 (IChO Team - July): Top 4 from Study Camp selected; top alternates (5th and 6th ranked) designated

Materials Needed

• School enrollment verification
• Age verification (birth certificate or ID)
• Citizenship/permanent resident documentation (only for Study Camp/IChO eligibility)
• No essay, portfolio, or recommendation letters required

Timeline

Local Exam: Late February - mid-March 2027; National Exam: ~10-day window in mid-April 2027; Study Camp: Early June 2027 (two weeks); International Chemistry Olympiad: July 2027

Cost

Free to participate in Local and National Exams; Study Camp is fully funded for selected 20 students

What Judges Look For

• Raw problem-solving accuracy on multiple-choice section (60 questions, 90 minutes) - tests speed, breadth, rapid pattern recognition
• Free-response mastery (8 problems, 105 minutes) - particularly reaction-writing proficiency (organic, inorganic, biochemical contexts), quantitative chemistry, kinetics derivations, multi-step mechanisms
• Laboratory practical technique (90 minutes, hands-on) - procedural accuracy, data analysis, quantitative determination skills on real experiments (titration, qualitative analysis, kinetics measurements)
• Depth beyond AP Chemistry - understanding of college-level general chemistry, organic chemistry, analytical chemistry, physical chemistry (thermodynamics, kinetics, equilibrium), electrochemistry
• Problem-solving rigor - ability to apply multiple chemical models and heuristics, weigh competing approaches, and select appropriate methodology

Scoring

Part I (Multiple Choice): 60 questions, raw score weighted × 1.25. Part II (Free Response): 8 problems, raw score. Part III (Lab Practical): Raw score, weighted × 0.5 for Study Camp selection only. Study Camp Selection (top 20): Part I × 1.25 + Part II + Part III × 0.5. High Honors (top 50): Part I × 1.25 + Part II. Honors (top 190): Part I × 1.25 + Part II. Exact cutoff scores fluctuate annually based on exam difficulty.

Common Mistakes

• Insufficient preparation time between Local Exam (March) and National Exam (April) - study should be completed before Local Exam since there is minimal time between stages
• Neglecting organic chemistry and reaction-writing - Part II discrimination heavily depends on mastering reaction equations across all contexts; this is the main differentiator between Honors and High Honors
• Inadequate preparation for free-response section - many students focus only on multiple-choice and are unprepared for the 8 extended-response problems requiring detailed work
• Poor lab practical preparation - underestimating the hands-on section; requires familiarity with actual experimental procedures, not just theory
• Trying to memorize instead of understanding - USNCO tests conceptual mastery and problem-solving, not memorization; rote learning leads to failure on novel problem types
• Over-relying on advanced textbooks (Atkins Physical Chemistry, Housecroft Inorganic) - experts recommend Atkins/Zumdahl + Klein Organic Chemistry as sufficient; going beyond wastes time
• Burning out from excessive problem-grinding - attempting all past exams exhaustively leads to diminishing returns; selective, strategic practice is more effective
• Ignoring the three-part structure - each part (MC, Free Response, Lab) requires distinct preparation strategies; treating them identically leads to imbalanced skill development

Acceptance Rate

~10,000-16,000 students take Local Exam annually; ~1,000 advance to National Exam (~6-10% local exam pass rate); ~190 earn Honors or High Honors (~1.2% of all participants); ~20 invited to Study Camp (~0.125% of all participants); ~4 selected for IChO team

Applicants

Approximately 10,000-16,000 students take USNCO Local Exam each year across all ACS Local Sections

Winners / Selected

50 High Honors; 190 total Honors; 20 Study Camp invitations; 4 IChO team members; 2 alternates

• Start studying 12-18 months before the National Exam for competitive performance (Honors or High Honors); begin immediately after taking Local Exam if advancing
• Take all past USNCO exams (1999-2025) under timed conditions to build speed and pattern recognition - the dcho.us Reaction Writing Study Guide provides all 163 Part II reaction-writing questions with worked answers
• Master Part II reaction-writing early (November-December) - this is the primary discriminator between Honors and High Honors; use first-principles framework rather than memorization
• Use free dcho.us resources: Reaction Writing Study Guide, Lab Practical Guide (2015-2025), Recommended Textbooks list, and USNCO Insider (selection mechanics)
• Review exam results systematically after every practice test: Did I get lucky? Did I miss a fundamental skill? Could I have eliminated options and guessed better? Fix identified gaps before the next attempt
• Prepare organically using college-level textbooks: Atkins/Zumdahl General Chemistry + Klein Organic Chemistry + chapters 27-38, 40 of Clayden - these are sufficient for IChO preparation
• Tackle IChO Prep Problems strategically (A-tier 2008/2016 and 2019 are most USNCO-relevant) and past IChO exams (2016 is best for USNCO practice) only after mastering all past USNCOs
• For Lab Practical preparation: study the dcho.us Lab Practical Guide covering 2015-2025 procedures and scoring; practice actual hands-on techniques if possible with a chemistry teacher
• Incorporate deliberate spaced repetition: return to weak areas multiple times rather than one-time drilling; space practice over months, not days
• Join study communities (r/USNCO on Reddit, Discord servers with 4,000+ STEM competitors) for motivation, peer explanation, and shared resources
• Use the dcho.us Find Your Level wizard (2 minutes) to get personalized preparation recommendations based on current skill level
• Don't skip the multiple-choice section during National Exam prep - it's weighted heavily (× 1.25) and determines who makes top 150 before free-response is even graded
• For Local Exam qualification: 6-12 months focused review of high school chemistry with emphasis on breadth and rapid multiple-choice technique is typically sufficient
• Study strategically by topic progression: general chemistry fundamentals → stoichiometry/equilibrium → kinetics/thermodynamics → electrochemistry → organic chemistry → lab techniques
• Get 8+ hours sleep before exam day, carefully review each problem during the exam, don't panic under time pressure - mental stamina matters in 5.5-hour testing days
• If targeting Study Camp: plan multi-year commitment starting 9th or 10th grade; cover advanced organic mechanisms, statistical thermodynamics, inorganic structure, and analytical lab work year-round

How to Prepare

• Phase 1 (Local Exam Prep, 6-12 months before March): Build foundational chemistry mastery through AP Chemistry textbook or honors chemistry course; practice past Local Exams under timed conditions; focus on breadth and rapid multiple-choice technique
• Phase 2 (National Exam Foundations, December-January): Begin systematic review of all chemistry topics; start taking past National Exams under timed conditions; identify weak areas through missed problems
• Phase 3 (Part II Free-Response Mastery, November onward): Study reaction-writing framework systematically using dcho.us Reaction Writing Study Guide; practice all 163 Part II reaction-writing questions from 1999-2025; master quantitative problem-solving (thermodynamics, kinetics, mechanisms)
• Phase 4 (Lab Practical Familiarization, January-March): Review dcho.us Lab Practical Guide covering 2015-2025; learn common lab procedures (titration, qualitative analysis, kinetics); practice with actual lab equipment if possible with chemistry teacher
• Phase 5 (Intensive Mock Exams, February-March): Take full National Exams (all three parts) weekly under realistic timed conditions; analyze every mistake; revise weak conceptual areas before actual exam
• Phase 6 (Study Camp Prep, April onward if qualified): Work through past IChO Prep Problems and IChO exams; study advanced organic chemistry (Clayden chapters 27-40); practice two-week intensive study schedules; take 2-3 mock IChO exams

Resources

• Official dcho.us resources (free): USNCO Reaction Writing Study Guide (all 163 Part II questions, 1999-2025), USNCO Lab Practical Guide (2015-2025), Recommended Textbooks list, USNCO Insider page, Find Your Level wizard, Decoding of Chemistry Olympiad YouTube series
• Textbooks: Atkins/Zumdahl Chemical Principles (general chemistry), Klein Organic Chemistry (organic mechanisms), Clayden et al. Organic Chemistry (advanced, chapters 27-40 for IChO)
• Past Exams: All past USNCO Local and National Exams (1999-2025) available free online through ACS; all IChO Prep Problems and IChO exams searchable at isodn.org and official IChO website
• Online Platforms: Cartesian Tutor (interactive USNCO practice with AI hints and grading); ChemWOOT (rigorous theoretical preparation); CODsite (intermediate-to-advanced problem explanations and ranking)
• Communities: r/USNCO subreddit, Discord servers (4,000+ STEM competitors), study groups formed through local chemistry clubs or schools
• YouTube: 'Decoding of Chemistry Olympiad' (Dr. Chen's free video series covering USNCO problems, reaction-writing strategy, lab preparation, challenging topics)
• Commercial Coaching: Dr. Chen's Academy offers three-tier programs (Level 2: Local Prep, Level 3: National Prep, Level 4: Camp Prep) with outcomes of 10+ IChO medalists and 40+ Study Camp qualifications over 15+ years; pricing varies by level
• Teacher Resources: ACS USNCO Teacher Training Course (online, self-paced); local ACS section contacts for exam administration and student support

Time Needed

Local Exam qualification: 6-12 months of consistent study (10-15 hours/week) from a student with solid high school chemistry foundation. National Exam Honors/High Honors: 12-18 months of focused preparation (15-25 hours/week) covering organic, physical, and analytical chemistry. Study Camp/IChO team: Multi-year commitment (typically starting 9th-10th grade, 20-30+ hours/week for competitive students), with year-round practice including frequent mock exams and advanced textbook study. Intensive Study Camp: 2-week immersive program in June with all-day instruction, lab work, and exams.

Successful USNCO participants typically have strong foundational chemistry knowledge (AP Chemistry 5 or equivalent), exceptional problem-solving skills that extend beyond school curriculum, and sustained motivation for 12-18+ months of deliberate practice. High Honors and Study Camp qualifiers generally demonstrate: mastery of college-level general chemistry, organic chemistry through introductory mechanism level, comfort with multi-step calculations and derivations, strong performance on timed exams, hands-on laboratory skills, and ability to apply chemistry concepts to novel problem types. Study Camp invitees are among the top <0.2% of participants and often go on to attend elite universities (MIT, Stanford, Caltech, Harvard, Johns Hopkins, etc.) and pursue chemistry, biochemistry, or related STEM fields. Past IChO medalists include Dr. Chen (dcho.us founder, 2007 silver medalist), Anugrah Chemparathy (2020 IChO gold medalist, CODsite contributor), and numerous MIT and Stanford chemistry majors. Successful competitors typically start preparation in 9th-10th grade for Study Camp selection, though National Exam qualification can be achieved with one year of focused prep from a 11th grader with strong chemistry foundation.

USNCO qualification is highly prestigious in college admissions and strongly correlated with admission to top universities. Study Camp qualification (top 20 nationally) is considered a 'tremendous accomplishment and a ticket to most Ivy+ colleges' according to past IChO medalists. National Exam Honors/High Honors placement (top 190) is viewed as a strong signal of exceptional chemistry ability. IChO team selection (top 4) and especially medal wins represent the pinnacle of high school chemistry achievement and virtually guarantee admission to elite STEM programs. College admissions officers recognize USNCO as one of the most competitive and rigorous science olympiads, comparable to USAPhO (Physics) in difficulty and more difficult than USABO (Biology). Unlike many high school competitions, USNCO demonstrates sustained mastery, problem-solving depth at college level, and genuine scientific capability rather than test-taking skills. Study Camp participants regularly attend MIT, Stanford, Caltech, Harvard, Johns Hopkins, UC Berkeley, and similar elite institutions. USNCO performance is particularly valued by chemistry, biochemistry, and pre-med programs. The rigorous preparation also develops genuine chemistry understanding applicable to future academic and professional success, lending authenticity to the credential.

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