Crime Busters

Crime Busters is a forensic chemistry event. A team of up to two students receives a scenario, a set of evidence and a list of suspects. The evidence is a collection of unknown solids, metals and liquids, fibers, plastics, hair, paper chromatograms and crime-scene material. You run tests on it, then write an analysis that links the evidence to a suspect and explains why the other suspects are not the culprit. Half of the points come from identifying the unknowns in the lab. A quarter comes from the written analysis. It rewards careful observation, correct chemistry and a conclusion you can defend with two or more tests that agree.

This guide follows the Division B Crime Busters rules in the 2027 rules manual (printed pages B16 and B17). Crime Busters is a Division B event, so Division C-tagged material in the question bank is background practice only (see the testing section). The 2027 rules keep the same five-part structure, unknown lists, evidence topics and score weights as last season. The main change is the iodine reagent the supervisor supplies, which may now be either iodine dissolved in potassium iodide solution or a 2% tincture of iodine. The 2027 rules also state outright that each participant may bring writing utensils. Always check soinc.org for clarifications posted during the season.

Event format

Teams that skip the listed equipment may be at a disadvantage, and supervisors can penalize up to 10% for prohibited equipment. A penalty of up to 10% also applies if the bench and waste are not handled as the supervisor directs.

What the rules cover

The competition has five parts, each covered in its own section below. Part 3.c is qualitative analysis of unknown solids, metals and liquids; 3.d is hair, fibers and plastics; 3.e is paper chromatography; 3.f is crime-scene physical evidence; 3.g is the written analysis. The topics stay the same at every level. What grows from Regional to National is the number of items in each part, the number and size of the mixtures, the number of chromatography types and the number of physical-evidence topics in play. Questions may only cover the evidence topics that actually appear in that competition.

Mixtures are built only from the starred solids in the 2027 rules (everything on the solids list except anhydrous sodium acetate, yeast and vitamin C). Metals and liquids are never mixtures. A "chromatography type" means a kind of sample, such as pen ink, a juice or a drink mix. A "physical-evidence topic" is one of the five areas in 3.f: fingerprints, DNA, shoeprints and tire treads, soil, and spatters. At a Regional you may see only one or two of those five, so prepare all five but expect a subset. The written analysis is required at every level.

3.c: unknown solids, metals and liquids

Every team gets the same unknowns. The scenario says which containers hold mixtures and whether a mixture has two or three materials. The solids come from a fixed list (anhydrous sodium acetate, yeast, vitamin C, calcium carbonate, table salt, sugar, flour, gypsum, cornstarch, baking soda, powdered gelatin, powdered Alka-Seltzer, and white sand). The metals are non-powdered pieces of aluminum, iron, zinc, magnesium, copper and tin. The liquids are lemon juice, isopropyl rubbing alcohol, 3% household ammonia, water, vinegar and 3% hydrogen peroxide. You identify them by solubility, acidity, magnetism, color, density and odor.

Part 3.c is half of the score, so it deserves most of your practice time. Its tests are simple; the skill is running them in a clean sequence and recording every observation.

Scoring and what it means for strategy

The manual gives approximate weights for each part. Your team's score is roughly a weighted sum of the fraction of points you earn in each part.

Three strategy points follow from the weights. First, do not sink the whole hour into one unknown; the points are spread across many items. Second, the tiebreaker goes to 3.g, so reasoning quality decides close results. Third, the analysis depends on the earlier lab results, so the lab must be organized enough that you can cite each observation in your write-up.

Foundations: thinking like a forensic chemist

The method is simple to state and harder to execute: observe before you react, test in an order that does not destroy evidence, record each result as you get it, and draw the smallest conclusion the data support.

Observation comes first. Color, texture, luster, magnetism and density are free: they consume no sample. Solubility and pH come next, because they need only water and indicator paper. Reagents such as 1 M HCl or iodine solution come after that, because they change the sample. Heating is last, because it can destroy the evidence. This order is a sensible default, not a rule in the manual.

Every test should discriminate. A test that gives the same answer for most candidates tells you little. The best tests split the list quickly: an acid test sorts carbonates from non-carbonates, an iodine test sorts starch from sugars and salts, and a magnet sorts iron from the other metals. Write the narrowed list down after each test.

Treat a single result as a lead, not an identity. Several white solids fizz, several dissolve, and several contain starch. A conclusion gets stronger when two or three independent observations point the same way, and the analysis in 3.g depends on that habit.

Qualitative analysis: the unknowns

Solids: behavior to check against

The table below lists typical behavior for the pure substances on the solids list. Run the same tests on references under the same conditions, and compare your unknown to the reference, not to your memory of the table.

Read the table as a decision tree. A solid that fizzes with acid is a carbonate or bicarbonate, or a mixture containing one. A solid that turns blue-black with iodine contains starch. A solid that dissolves completely without fizzing is a salt, a sugar or an acid, and its pH tells you which (vitamin C acidic, sodium acetate slightly basic, table salt and sugar neutral). A solid that stays as a cloudy suspension in water is either insoluble or a starch or protein powder that does not truly dissolve. The one solid that fizzes in plain water is powdered Alka-Seltzer, which carries its own acid. The decision keys are the core of the solids work, and you should build your own flow chart before the event so you are not improvising.

Mixtures of solids

At every level some containers may hold a mixture of starred solids (two solids each at Regional, two or three at State and National), and the scenario tells you which containers and how many components. The method is to subtract. Each test either shows that a component is present or rules one out, and you keep running tests until every component is accounted for.

1. Observe color and grain under the hand lens. Look for two textures.
2. Stir a small sample in water. Note what dissolves, what stays cloudy and what settles as a residue.
3. Run iodine on a separate sample: blue-black means starch (cornstarch or flour) is in the mixture.
4. Run 1 M HCl on a separate sample, and again on any water residue: fizz means carbonate or bicarbonate somewhere in the mixture.
5. Test the pH of the water solution, and flame-test it if a flame is available.

Acids, bases and the fizz test

The fizz test is the most discriminating reaction on the list, and it is also the one people misread. Carbonates and bicarbonates react with acid to produce carbon dioxide gas, which you see as bubbles. Calcium carbonate reacts with hydrochloric acid according to:

$$\text{CaCO}_3(s) + 2\,\text{HCl}(aq) \rightarrow \text{CaCl}_2(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)$$

Baking soda reacts the same way, with one molecule of acid per bicarbonate:

$$\text{NaHCO}_3(s) + \text{HCl}(aq) \rightarrow \text{NaCl}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)$$

The gas is the signal. A fizz with acid tells you that a carbonate or bicarbonate is present. It does not tell you which one. You separate them with solubility: calcium carbonate is practically insoluble in water, while sodium bicarbonate dissolves. Then you separate them with solution pH: the sodium bicarbonate solution is mildly basic, which pH paper will show.

Acidity and basicity are measured with pH paper or with a visible indicator. Vitamin C, lemon juice and vinegar give acidic solutions. Household ammonia and solutions of carbonate or bicarbonate give basic ones. Water is neutral.

Iodine and starch

The supervisor supplies the iodine reagent, either as iodine dissolved in potassium iodide solution or as a 2% tincture of iodine (iodine in alcohol). Both behave the same way for this test. Iodine reagent turns blue-black in the presence of starch. Starch is a polymer of glucose whose chains coil into a helix, and iodine molecules fit inside the coil. The blue-black color is the signature of that complex. Sugars, salts and most acids do not give this color. The iodine test is therefore a starch test, and a negative iodine result on a sugar is expected.

Cornstarch and flour both contain starch, so both turn blue-black; separate them with other observations. Cornstarch is close to pure starch, so its suspension is smooth. Flour contains protein and other plant material, so it clumps when wet. Two observations are required before you commit.

Sugars and Benedict's test

Benedict's solution is a copper(II) reagent in a basic solution. When it is heated with a reducing sugar, copper(II) is reduced to copper(I) oxide, which forms a brick-red precipitate. The color moves from blue (no reduction) through green and yellow to orange and brick red as more reducing sugar is present. The figure below shows the standard series.

The key fact for this event is that table sugar (sucrose) is a non-reducing sugar. Its molecule does not have the free aldehyde or ketone group that reduces Benedict's reagent, so sucrose gives a negative result, staying blue. Glucose and fructose, by contrast, are reducing sugars. Many teams expect every sugar to turn Benedict's solution brick red and then misidentify the sugar. The Benedict's reagent is supplied by the supervisor only if the supervisor chooses to provide it, so do not build a plan that depends on it.

Metals

The metals are aluminum, iron, zinc, magnesium, copper and tin, as non-powdered pieces. Start with physical properties, which cost nothing. Iron is the only one of the six attracted to a magnet. Copper is the only one with a reddish-brown color. The other four are silvery, and density separates them well: the table gives typical values to compare against (look up the exact numbers in a reference, since they vary slightly by source and alloy).

Chemistry sorts the rest. A metal above hydrogen in the activity series displaces hydrogen from acid, and the bubbles are hydrogen gas:

$$\text{Mg}(s) + 2\,\text{HCl}(aq) \rightarrow \text{MgCl}_2(aq) + \text{H}_2(g)$$

Copper lies below hydrogen and does not react with dilute hydrochloric acid, which is why "no bubbles" is a useful result. Aluminum and zinc are also amphoteric: they dissolve in strong base as well as in acid, releasing hydrogen. The supervisor provides only 1 M HCl, so a base test will usually be given to you as a result, as in the archive tables that list "NaOH: produces hydrogen gas".

A common mistake is treating one reaction as the whole test. Aluminum and zinc both react with acid and with base, so you need a second feature. Tin is amphoteric too, though it reacts slowly; a base result alone does not single out Al or Zn. The densities of aluminum and zinc differ by a factor of about 2.6, so a density comparison (or simply the heft of the piece) separates them cleanly. Zinc (7.1) and tin (7.3) are too close in density to separate that way, so use reaction rate with acid and the feel of the metal. Iron, tin and zinc can be told apart quickly: iron is magnetic, and zinc reacts with acid much faster than tin.

Liquids

The liquids list has a clean set of tests. The table gives the pattern to expect; confirm each with a reference sample run under the same conditions.

Lemon juice and vinegar are the hard pair because both are acidic and both fizz with baking soda (the acid releases carbon dioxide from bicarbonate). Separate them by odor and by pH, and note that vinegar is the stronger-smelling and clearer of the two. Ammonia is the only basic liquid on the list. Rubbing alcohol mixes with water in all proportions, so a miscibility test with water does not separate it from the others. Hydrogen peroxide decomposes into water and oxygen:

$$2\,\text{H}_2\text{O}_2(aq) \rightarrow 2\,\text{H}_2\text{O}(l) + \text{O}_2(g)$$

The decomposition is much faster in the presence of a catalyst. Yeast contains an enzyme, catalase, that speeds the reaction, so a yeast suspension foams when added to hydrogen peroxide. The foaming is real information, but it points two ways. If you already know the liquid is peroxide, foaming identifies the powder as yeast. If you already know the powder is yeast, foaming identifies the liquid as peroxide. Confirm one side by another test (for example, peroxide has no pH signature but yeast gives a cloudy suspension) before you use it to name the other.

Polymers and natural materials (3.d)

Hair

Hair has three layers to examine. The outer cuticle is made of overlapping scales. The cortex is the bulk of the shaft and contains the pigment (melanin) and the structural protein keratin. The medulla is a central core that may be continuous, fragmented or absent. Under magnification you compare the scale pattern, the diameter of the shaft and the structure of the medulla.

The medullary index is the ratio of the medulla's width to the hair's width. It is a ratio, so it has no units, and it is the standard way to make the medulla comparison quantitative:

As commonly taught, human hair has a narrow, fragmented or absent medulla, so its medullary index is small (roughly one third or less). Dog and cat hair usually have a wider, more continuous medulla, with an index around one half or more. Cat hair is often described as having a segmented or 'string of pearls' medulla and dog hair a wide, continuous one (a ladder pattern is the classic rabbit example), and the scale patterns differ as well, but treat these as clues to support the index rather than a stand-alone identification. Your reference sheet or the test's data supplies the cut-offs; use them if they differ from these.

The 2027 rules ask only whether a hair is human, dog or cat. They do not ask for specific hair types such as guard hairs, so spend your practice time on telling those three apart from the medulla, the scale pattern and the shaft width. Some older tests also ask about the hair growth cycle (anagen, catagen and telogen) and about growth rate (roughly one centimeter per month). That is background reading, not part of the 2027 outline.

Fibers

Fibers fall into three classes. Animal fibers are proteins, such as wool and silk. Plant fibers are cellulose, such as cotton and linen. Synthetic fibers are man-made polymers, such as nylon, polyester and acrylic. The table compares their most useful clues.

The burning clues have a chemical reason. Proteins contain nitrogen (and wool also sulfur), so burning them releases compounds that smell like burnt hair. Cellulose is a carbohydrate and burns to carbon dioxide and water with the smell of burnt paper or wood. Synthetic polymers melt before they burn, which is why they bead and drip rather than leaving ash.

Plastics

The recyclable plastics on the list each carry a resin code: PETE (1), HDPE (2), PVC (3), LDPE (4), PP (5) and polystyrene (6, non-expanded here). PMMA (acrylic) is not part of the common recycling codes, but it is on the event list. Burn tests are not performed by participants, but results may be given to you, and the supervisor may supply density solutions for a float-and-sink series. The table lists typical densities and burn clues; burn descriptions in tests are worded in many ways, so decide from the whole set of clues.

The density column is the reliable one. Polyethylene (HDPE and LDPE) and polypropylene are simple hydrocarbons that pack loosely, and all three float in water. PETE, PVC, polystyrene and PMMA are denser than water and sink, though polystyrene barely does. Remember "Floats: PE and PP; sinks: the rest" as your first split, then separate within each group using burn clues. Density solutions let you bracket a plastic's density more finely than a float-or-sink test does.

Paper chromatography (3.e)

The 2027 rules use evidence such as pen inks, juices and drink mixes like Kool-Aid. Your chromatograms are handed in with the score sheet, and you are expected to work out Rf values, so label each strip and mark its origin and solvent front clearly.

In paper chromatography, a solvent climbs a strip of paper by capillary action. The paper holds water on its fibers and is the stationary phase; the moving solvent is the mobile phase. Each dye in an ink or juice divides itself between the two phases. A dye that dissolves well in the solvent and sticks weakly to the paper travels farther. Different dyes separate because they have different partition behavior.

Spots are compared with the retention factor, Rf:

Because a spot is a blob, measure to the center of the spot every time and use the same ruler for both distances. Report Rf to two decimal places at most, since the measurement itself has about that precision. A higher Rf means the dye is more strongly drawn into the moving solvent than held by the paper. A spot with Rf near 1 barely stuck to the paper, and one near 0 barely moved.

Rf values are only comparable when the solvent, paper, temperature and origin position are the same. Mark the solvent front immediately after you remove the paper, because solvent evaporates from the paper and the front moves in the record. Keep the origin line above the solvent level, since a dye that starts in the solvent dissolves into the pool. If you are given two inks that run the same, you have two observations that agree, and the analysis can cite both.

Physical evidence (3.f)

Fingerprints

Friction ridges fall into three pattern classes. A loop has ridges that enter from one side, curve back and exit on the same side. A whorl has ridges that form circles or spirals. An arch has ridges that enter from one side and exit the other with a rise in the middle. Loops are the most common class, roughly 60 to 65% of people, then whorls at roughly 30 to 35%, with arches the rarest at about 5%. Two landmarks help you classify. A core is the center of the pattern, and a delta is the triangular spot where ridge flows meet. A loop has one delta, a whorl has two or more, and a plain arch has none.

Beyond the pattern class, examiners compare minutiae: the points where ridges end or split. A ridge ending and a bifurcation (a split) are the most common. The manual asks only that you recognize loops, whorls and arches, and you can note minutiae qualitatively where the scenario supports it. Do not claim a number of matching points, because the event does not ask for a match statistic. Pattern class alone cannot identify a person, because millions of people share each class; it only excludes or narrows.

Prints also differ by how they were left. A patent print is visible without treatment, such as a bloody or ink print. A plastic print is an impression in a soft material such as wax or paint. A latent print is invisible and must be developed. Latent prints need development methods that match the surface. Fingerprint powder adheres to the oily residue left by the skin and suits smooth, non-porous surfaces. Iodine fuming deposits a brown stain that fades. Cyanoacrylate ("superglue") fuming forms a white deposit on non-porous surfaces. Ninhydrin reacts with the amino acids in sweat to give a purple color and is used on porous surfaces such as paper (ninhydrin is one of the most frequent correct answers in the archive, with 19 questions). Wet-surface powder suspensions are used where a surface is wet.

DNA evidence

DNA evidence in this event is about comparing profiles. The scene sample and each suspect give a chromatogram or electropherogram, a graph of peaks at specific positions (loci). Forensic profiles are built from short tandem repeats (STRs), stretches where a short sequence repeats a variable number of times. Each peak marks an STR length (an allele). You inherit one allele per locus from each parent, so at each locus a person shows two peaks, or one taller peak if both alleles are the same length. A sample that shows three or more peaks at several loci suggests more than one person contributed.

Matching means the peaks line up at the same loci. A suspect whose peaks differ at even one locus is excluded from that comparison. A suspect whose peaks match at every locus is consistent with the sample, but the event does not ask you to estimate how rare that profile is.

Two lab steps explain the graph, and you need them only as background for reading it. Polymerase chain reaction (PCR) copies a targeted stretch of DNA many times over repeated heating and cooling cycles, using a heat-stable enzyme (Taq polymerase). Gel electrophoresis then separates DNA fragments by size. DNA carries a negative charge from its phosphate backbone, so it moves toward the positive electrode, and smaller fragments move farther through the gel.

Footwear, tire treads and soil

Shoe prints and tire treads are compared by two kinds of features. Class characteristics are shared by every item of that type, such as the tread design and size. Individual characteristics are acquired through use: wear patterns, cuts, nicks and embedded stones. A class match only says the shoe could be the one; individual features make the link stronger. Impressions also carry movement clues. Stride length grows with speed, a runner puts more weight on the toe, and smearing or drag marks show direction. Treat these as tentative, qualitative conclusions: the manual says you do not perform speed calculations on footwear. Tire treads work the same way, with tread pattern and wear linking to a vehicle and skid marks showing direction of travel.

Soil is compared by its composition, color, texture and particle size as the scenario describes them. A soil sample from a suspect's shoe or car is consistent with a scene location only if several features match. Soil is supportive evidence: it can exclude a location with certainty when the composition differs clearly, but a match rarely identifies one place by itself.

Spatter and bloodstains

Spatter analysis links the shape of a drop to how it moved. A drop that falls straight down strikes the surface with little sideways motion, so its stain is round with no tail. A drop that hits at an angle leaves an elongated stain with a tail, and the more it is stretched, the shallower the angle. The narrow end, or tail, points in the direction the drop was travelling, so the source lies on the opposite side of the stain from the tail. Small satellite drops around a main stain mean the drop struck with enough force to throw off smaller droplets.

Velocity shows in drop size and spread. Crime-scene texts usually group spatter by the energy that made it: low velocity (drips and passive stains, large drops of about 4 mm or more), medium velocity (blunt-force impacts and cast-off, medium-sized drops) and high velocity (such as a gunshot, a fine mist of tiny drops). If a question gives you a photo, ask first whether the drops are large and few or small and numerous. A set of stains with different shapes, sizes and angles suggests more than one event or more than one direction of motion. An archive question about a suspect who claims one event has the key "multiple events with different velocities or angles."

The manual says spatter speed and direction should be analyzed without calculations. Answer in words: round drop (vertical fall), elongated drop (angled impact), satellite spatter (force at impact), large drops (low velocity), fine mist (high velocity).

Writing the crime-scene analysis (3.g)

The analysis is scored for reasoning, so write it as an argument. A structure that works under time pressure has five parts.

1. Claim. Name the suspect you conclude is responsible, in one sentence.
2. Evidence. List each piece of evidence that implicates that suspect, and cite the test or observation that supports it. Use your table.
3. Consistency. For each conclusion, cite at least two observations or tests that agree. This is the step that separates an analysis from a list.
4. Exclusion. Explain why each other suspect is not chosen. A single exclusion (a DNA peak that differs, an Rf that does not match) is enough for that suspect.
5. Uncertainty. Name one alternative explanation or one limitation, such as recall, contamination, or a test that was not conclusive.

The supervisor may also add other crime-scene analysis questions to Part 3.g, so leave time for them after the main write-up.

Strategy: splitting the work and the time

Two students can cover the whole event if each person understands all of it, because the analysis draws on every lab part. A practical split is one partner on the 3.c unknowns (the highest-weighted part), while the other runs the chromatography, which takes time to develop, and the physical evidence questions. Both record observations in the same team table. Start slow tests (chromatography, anything that needs drying) early so they run while you do other work.

Plan the time. Spend the first minutes on the safety check and reading the scenario, because it tells you which containers are mixtures and which evidence matters. Then run the 3.c tests in the order above and fill in the table as you go. Reserve the last part of the period, not the last few minutes, for the analysis, since 3.g is a quarter of the score. Clean up as the supervisor directs, because a penalty of up to 10% applies to messy benches.

The cheat sheet is one letter-size sheet, both sides. Do not spend it on the answers to specific unknowns, because the list changes between tournaments. Spend it on decision keys: a flow chart for the solids, the fiber burn table, the plastics density and burn table, the Rf formula with a reminder about the origin line, the Benedict's and iodine color meanings, the metal reaction and density table and the fingerprint classes.

Common pitfalls

The most common wrong answers in the archive reflect a few recurring mistakes. The items below are drawn from the most frequent correct answers (synthetic, PETE, animal, cornstarch, sodium acetate, PVC, vegetable, vitamin C, calcium carbonate) and from the wrong statements that appear most in true-or-false questions.

How tournaments test this

The archive has 5,789 Crime Busters questions from public tournaments, and the question bank has 16,269 prompts. They look different. The archive is almost all Division B (5,748 of 5,789, or 99.3%), while the question bank is tagged mostly Division C (12,584 prompts, or 77.3%) and Division B (3,642, or 22.4%). The archive is the better guide to the current Division B format. Treat the bank's Division C-tagged prompts as extra practice on the same chemistry and evidence topics, and check any unfamiliar topic against the current manual before you rely on it.

Most of the test is free response, and most of that is explanation. In the archive, the largest tagged task is "explain or why" at 9.1% of questions, followed by calculate at 1.5% and "which of the following" at 1.2%. Only about 15% of archive questions carry a task tag at all, so treat those shares as a floor. The question bank tags a larger share of explain-or-why prompts (11.6%), which fits the written emphasis.

Subtopic counts show where the weight sits. In the archive, Evidence Analysis is tagged on 3,041 questions (52.5%), Chemistry Lab on 2,269 (39.2%), Crime Scene on 716 (12.4%), Fingerprints on 525 (9.1%) and DNA on 309 (5.3%). The tags overlap, so the percentages sum to more than 100. In the question bank, Evidence Analysis dominates at 9,367 prompts (57.6%) and Chemistry Lab follows at 2,647 (16.3%).

Recent seasons dominate. Of the archive questions, 65.2% come from the 2024, 2025 and 2026 seasons (814, 1,110 and 1,848 questions). The 2026 season alone supplies 31.9%, so practice on recent tests as well as older ones.

The recurring terms show what writers return to. "Hair" appears in 1,583 prompts across the archive and the bank, "chemical" in 1,414, "powder" in 1,357, "blood" in 1,168, "fingerprint" in 843, and "fingerprints" in 701 more. Multi-word terms tell the same story: "flame test" appears in 391 prompts, "paper chromatography" in 224, "burn test" in 204, "Benedict solution" in 181, "gel electrophoresis" in 168 and "medullary index" in 98. Two terms appear in the prompts but are not in the Division B outline: "mass spectrum" (93 prompts across the archive and bank) and "thin layer chromatography" (50 prompts). Expect them only as data a scenario supplies.

Question style is consistent. A table-driven identification asks you to name an unknown from its test results ("UNKNOWN FABRIC J... Flame test: self extinguishing: NO, chars, smell burning paper, ashes gray... fabric type"). A true-or-false statement tests a misconception, such as "all ionic powders dissolve readily." A multi-select asks which techniques reveal prints or which forces influence a result. A free-response prompt asks you to explain a mechanism in a sentence or two. Practice all four, because free response is nearly nine times as common as multiple choice in the archive (4,983 versus 566 questions).

Among the most frequent correct answers are synthetic (47 questions), PETE (42), animal (38), cornstarch (30), sodium acetate (29), PVC (27), vegetable (26), vitamin C (25) and calcium carbonate (24). These are the identities you are most likely to see, and they are the ones your decision keys should handle quickly.

Practice on several tournaments rather than one. The archive's top sources are invitationals such as the Mason Satellite Invitational (2025, 155 archived questions), the Rickards SO Invitational (2023, 133) and the Rickards Mini Invitational (2022, 124). Of the archive questions, 1,616 have official answers that the site trusts for quizzes, and the quiz below uses only those.

Test yourself

These questions come from public tournament tests in the Scio.ly archive. Click an answer to check it; each links to the full test. Explanations appear where the reasoning is not obvious.

Test yourselfUnknowns: solids, liquids, metals and plastics

0 / 0 correct

1. 1

   True or False: Dissolving larger amounts of vitamin C in H₂O will increase the OH⁻ concentration of the solution. Sodium bicarbonate will do the opposite.

   Question 1 options

   ATrueBFalse

   From: Rickards SO Invitational, 2022-23, Division B

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Test yourselfFibers, hair and crime-scene physical evidence

0 / 0 correct

1. 1

   UNKNOWN FABRIC J Location: Fred's Closet TESTS: Flame Test: self extinguishing: NO, chars, SMELL: Burning paper, ASHES: Grey Microscope: FABRIC TYPE: ____

   Question 1 options

   AanimalBplantCsynthetic

   From: High Desert Satellite, 2024-25, Division B

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References and further reading

• Science Olympiad, 2027 Division B rules manual (Crime Busters, pages B16 and B17) and the Division B Chemistry Events Lab Equipment List: https://www.soinc.org
• Science Olympiad store, for recommended resources: https://store.soinc.org
• SciOly Wiki, Crime Busters (another summary of the event; compare it with the manual): https://scioly.org/wiki/index.php/Crime_Busters
• OpenStax, Chemistry 2e (acids and bases, solubility, redox and the activity series): https://openstax.org/details/books/chemistry-2e
• OpenStax, Biology 2e (DNA structure, PCR and electrophoresis): https://openstax.org/details/books/biology-2e
• National Human Genome Research Institute, Genetics Glossary (PCR, electrophoresis, STR and other terms): https://www.genome.gov/genetics-glossary
• National Institute of Justice, forensic science resources (crime-scene evidence and physical evidence methods): https://nij.ojp.gov
• Practice more: the Scio.ly test archive has many public Crime Busters tests; filter for recent seasons and read the official keys.