The Danish Chemistry Olympiad has existed since 1982 and consists of 5 rounds with three selections (preliminary, semifinal and final). The entire competition season starts in mid-November and ends May where the national team is determined. The national team continues with training to Nordic Chemistry Olympiad (NChO) and the International Chemistry Olympiad (IChO) which are held in July or August. Figure 1 shows an overview of the structure and rounds of the competition.

Figure 1: An overview of the structure and rounds of the Danish Chemistry Olympiad. In the first round, everyone can participate. The 60 highest scorers are sent on to the semifinals. Here, the 14-16 best are selected for the finals, where the four best participants are found over three rounds to form the national team. The national team then participates in two international competitions, NChO and IChO

For the Danish Chemistry Olympiad, there are two rules for participation. The first is that all high school students can participate in the 1st and 2nd rounds regardless of age. If the student is over 20 years old on the first of July of the given year, he or she can not participate in the final rounds, NChO and IChO. The age limit is an international rule set by IChO. The second rule is that there can be a maximum of four students from each school for the 2nd round, three students for the final rounds and a maximum of two students among the four who make up the national team.

## Preliminary Round (1st Round)

The preliminary round is held every year in mid-November locally at schools, and everyone can participate. One of your school’s chemistry teachers will hold the exam. If your school does not regularly participate in the Chemistry Olympiad, please contact your chemistry teacher. The first round consists of a 120 minute theoretical test of approximately seven tasks divided into around 30 total parts. The test allows limited aids in the exam: Formula Collection Chemistry A (both 1st and 2nd edition), DATA book physics & chemistry and a calculator or PC / MAC with CAS tool (Maple). Using books and notes during the exam is therefore prohibited. Participants are not expected to do all the tasks correctly or respond to all tasks. A general rule of thumb is that a score over 45% qualifies for the 2nd round.

The syllabus is everything from Chemistry A, including spectroscopy. Typical topics are stoichiometry, inorganic chemistry, organic chemistry, chemical equilibrium, acid and base, reaction kinetics, thermodynamics and spectroscopy.

## Semifinals (2nd round)

The 60 highest scorers from round 1 get an invite around December to attend the 2nd round held the last weekend in January, from Friday to Sunday. A typical program consists of: the theoretical exam Friday, lectures followed by the practical exam and a tour of the Copenhagen University (KU) Chemistry Institute on Saturday and a ceremony on Sunday, concluding the round.

The theoretical exam consists of two parts in 120 minutes. Part 1 is 25 multiple choice questions and makes up 35% of the total theoretical score. Part 2 consists of a series of larger tasks in the same style as in the 1st round. The syllabus is the same as the 1st round but has 3-5 multiple choice questions in topics from the final rounds (3rd-5th round). The exam’s overall level is a bit higher than that of the 1st round. Permitted aids are: Formula Collection Chemistry A (both 1st and 2nd edition), DATA book physics & chemistry (Danish: Formelsamling Kemi A (1. and 2. edition), DATAbog fysik & kemi) and a calculator or PC/MAC with CAS tool (Maple).

The practical exam consists of 2 parts. The participant has 2 hours for each part with a break in between without any aids. Part 1 is a titration exercise where the participant can for example determine the concentration of a solution. Common titration types:

• Acid / base titration
• Redox titration Permanganate or Iodometric titration.
• EDTA titration (complexometric) with EDTA and an indicator like Eriochrome-T

Part 2 of the practical exam consists of a qualitative inorganic analysis sometimes referred to as “Ionjagt” eller “dryp-dryp kemi” in Danish (Eng. “ion hunting” or “drip-drip chemistry”), during which you are given 8 solutions and a list with 8 inorganic compounds they contain. The task is to determine which solution contains which inorganic compound by systematically mixing them and noting the result.

The total 2nd round score is 60% of the theoretical and 40% of the practical score.

The ceremony on Sunday will reveal which approx. 16 out of the approx. 60 participants will advance to the final rounds. During the event, diplomas, books, etc. are given out.

## The Final Rounds (3rd - 5th round)

The following 3 rounds constitute the final rounds, and the results, with and that of the 2nd round, decide who will be on the year's national team. The chemistry level in the finals corresponds to the 1st and 2nd year of Denmark’s bachelor in chemistry. Each of the rounds is held over an entire weekend, spaced approximately 1 month apart. The round structures are very similar to that of the 2nd round.

The order of the rounds may change, but in the last few years they have been in the following order:

## Round 3 (Aarhus University, AU round)

Round 3, also known as the AU round, is held around the end of February or beginning of March. It is all held over a weekend from Friday to Sunday at Aarhus University (AU) with accommodation. What is unique about this round is that it is themed and the participants are mainly tested in organic chemistry and a new topic. This topic is based on the IChO preparation problems published every year around the beginning of February. The last few years (2015-) this topic has been crystallography, but polymer chemistry has also emerged once.

In preparation, participants will be given a syllabi of organic chemistry based on the book McMurry’s Organic Chemistry by John E. McMurry, and related assignments that will set the exam's framework. For the new topic, participants will receive lectures followed by a problem-solving session. The typical program: Friday is spent on reviewing organic chemistry homework followed by a lecture with a problem-solving session on the new topic. Saturday consists of the practical exam, a 4-hour exam consisting of organic synthesis with TLC analysis and a titration determination of an unknown acid. After the exam, the participants have a guest lecture and tour of AU. Sunday is then a 4 hour theoretical test without any aids. Only paper, a pencil/pen and a calculator (without graph function) are allowed. The test consists of 20 multiple choice questions and contains topics from the previous rounds and 5 problems with sub-parts (example of distribution: 3 organic, 1 spectroscopy and 1 crystallography/polymer chemistry). The participant’s total score for the 3rd round is divided between 60% of the theoretical and 40% of the practical score.

Recommended preparation: Ch. 1-8. Fundamentals of Organic Chemistry, International Edition by John Mcmurry, 7th edition

## Round 4 (Technical University of Denmark, DTU round)

Round 4, also known as the DTU round, is held around the beginning of April. It is held over a weekend from Friday to Sunday at the Technical University of Denmark (DTU) with accommodation. This round is also themed, and the participants will mainly be tested on physical and coordination chemistry.

In preparation, the participants receive a booklet with assignments and short theory sections that set the exam framework. A typical program: Friday consists of lectures and problem-solving sessions in physical and coordination chemistry. Saturday is spent on a 4 hour practical exam consisting of inorganic synthesis (synthesis of a complex) and titration analysis on the synthesis product. Sunday wraps up round 4 with a 4-hour theoretical exam without any aids. Only paper, pencil/pen and calculator (without graph function) are allowed. The test consists of 10 multiple choice questions containing topics from the previous rounds and 8 problems with sub-parts. The total score for the 4th round is divided between 60% of the theoretical and 40% of the practical score.

Recommended preparation: The booklet for Chemistry Olympiad Round 4 (given by the Danish Chemistry Olympiad Committee)

## Round 5 (University of Copenhagen, KU round)

Round 5 is the lastround of the Danish Chemistry Olympiad.

The typical program: Friday, reviewing inorganic, organic, and expanded chemical equilibrium theory (mass and charge balances) followed by problem-solving sessions. Saturday, lecture in inorganic chemistry followed by problem-solving sessions. After inorganic chemistry, the participants will take the practical exam. Here the participants get approx. 4 hours to do a titration and a qualitative inorganic analysis just like in the 2nd round. Sunday is spent on the theoretical test of 5 hours without any aids. Only paper, a pencil/pen and a calculator (without graph function) are allowed. The exam consists of approx. 10 multiple choice questions and approx. 10 problems with sub-parts based on all topics. The participant’s total score for the 5th round is 60% of the theoretical and 40% of the practical score.

Recommended preparation: Ch. 9-12. Fundamentals of Organic Chemistry, International Edition by John Mcmurry, 7th edition and Basic Analytical Chemistry and the Chemistry of The Elements in Aqueous Solution by Peter Andersen and Ole Mønsted 2010 edition (Danish: Grundlæggende Analytisk Kemi og Grundstoffernes Kemi i Vandig Opløsning )

The Danish Chemistry Olympiad ends Monday with a ceremony where the national team consisting of the 4 highest scoring participants of the approx. 16 will be announced. The final score is calculated as follows:

$P_{tot} = 0.2 \cdot P_{\%}(R2) + 0.2 \cdot P_{\%}(R3) + 0.3 \cdot P_{\%}(R4) + 0.3 \cdot P_{\%}(R5)$

Where $P_{\%}$ is one's score in percent and $R\#$ represents teh round with its associated number. This ceremony is in conjunction with all the other science olympiads (mathematics, physics, biology, computer science, and geography).