|Question Marathon Threads|
|Division B Results|
In Crime Busters, students will identify perpetrators of a certain crime by identifying unknown powders, liquids, and metals, and analyzing hairs, fibers, plastics, fingerprints, DNA evidence, shoeprints, tire treads, soil and splatters. Students will also analyze evidence from paper chromatography. Students should be able to use this data to answer some questions about who committed the crime and how the evidence supports their argument. This event was previously known as Science Crime Busters, but was changed to Crime Busters after the 2009-2010 season.
- 1 Supplies
- 2 Before the competition (at school practices)
- 3 Charts
- 4 Mixtures
- 5 Chromatography
- 6 Fingerprints
- 7 Polymers
- 8 Fiber Analysis
- 9 Bloodstain Analysis
- 10 DNA
- 11 Soil
- 12 Shoeprints and Tire Tracks
- 13 Water Testing
- 14 Analysis
- 15 At the Competition
- 16 Scoring
- 17 Practice Tests
Every team must bring these safety items to be allowed to participate.
- Lab aprons or lab coats. If a team uses lab aprons, they must make sure to wear long sleeves that reach the wrists.
- Closed toe shoes, NO sandals
- Pants or skirts that cover the legs to the ankles
- Category C Goggles
Also, the team should and may have the following:
- One 8.5"x11" page with information on the front and back
- Writing instruments(pencils!)
- Paper Towels
- Microscope slides and cover slips
- Tweezers or forceps
- pH paper
- Hand lenses
- Test tubes and racks, spot plates, well plates, reaction plates, beakers, or similar small containers for mixing
- Something for scooping, stirring, and mixing
- Pipettes or droppers
- Graduated cylinders (10 mL and 25 mL)
- Conductivity meter (9V or less)
The supervisor will provide everything else needed, so if anything outside of what the rules allow is brought, a penalty may be issued.
Before the competition (at school practices)
Check with your SO coach to get the following materials to test:
- Powders (Italics means it can be used in mixtures)
- White Sand
- Calcium Carbonate
- Table Salt
- Baking Soda
- Powdered Gelatin
- Powdered Alka-Seltzer
- Sodium Acetate
- Vitamin C
- Rubbing Alcohol
- Household Ammonia
- Hydrogen Peroxide
- Lemon Juice
The coach will also need-
- a dropper bottle of 1M HCl (hydrochloric acid)
- a dropper bottle of Iodine
- pH or Litmus paper
- 15-20 unknowns
- 250 mL dH2O
- chromatography materials (chromatography paper, ink to be tested, extra beaker for testing)
Make a chart for testing. For powders, include color, reactions with water, HCl, and Iodine; odor (distinct, faint, or none); shape (crystalline, granular, or powder), solubility (whether it dissolves in water or not), and reaction to pH or Litmus paper. For metals, include reactions to HCl and magnetic property (yes or no). For liquids, include smell, reactions to pH or litmus, and color. With your teammate, memorize the results (this is where two heads are better than one) and try testing unknowns made by the coach or other team members. This helps very much when it comes time for the competition.
|Powder||Crystal Shape||Color||Solubility||pH||HCl||Iodine||Formula||Notes||Other Names|
|Sodium Acetate||powder - irregular shape||white||yes||~8||none||none||C2H3NaO2||exothermic when mixed with water and has a distinctive sweet odor|
|Sand||random||white||no||~6||none||none; bad odor||SiO2||does nothing, may have black specks|
|Calcium Carbonate||powder||white||no||~7-8||fizz||none; the color looks sort of like mustard/peanut butter||CaCO3||the powder it self is very airy and hole-y||Limestone, chalk, aragonite|
|Vitamin C (Ascorbic Acid)||grains||white||yes||~2||none||clears it||C6H8O6||may have a colored tint- green, yellow, pink, orange (if from tablets). Distinctive smell.|
|Salt||signature square grains||white||yes||~6-7||none||none||NaCl||delayed reaction with iodine (may be difficult to observe)||Table salt|
|Sugar||grains||white||yes||~6-7||none||none||C12H22O11||Similar to salt but grains are slightly rounded|
|Flour||powder||Off-white||no; lumpy||~6-7||none||blackens it - iodine clumps together, unlike cornstarch||(C6H10O5)n||Clumps with water|
|Cornstarch||powder||white||no - forms solid-liquid substance||~6-7||none||blackens it||C27H48O20||pure white, feels slippery|
|Gelatin||grains||light yellow||no; turns into gel||~6||none||none||C102H151O39N31||swells in water|
|Alka-Seltzer||powder||white||yes||~6-7||fizz||fizz||C16H17NaO14||fizzes with everything including water|
|Yeast||pellets||tan||no||~7||none||none||microorganism||generally easy to identify since it smells sort of like bread most of the time|
|Baking Soda (Sodium Hydrogen Carbonate)||powder||white||yes||~8||extremely fizzy for a long while||none; more red-brown than Plaster of Paris||NaHCO3||rough texture (kinda)||Sodium bicarbonate|
|Gypsum (Calcium Sulfate Dihydrate)||powder||white||no||~6||none||none||CaSO4· 2H2O||opaque bubbles and hardens in water||Plaster of Paris, alabaster|
Many powders have a "give-away" making them easier to identify:
- Alka-Seltzer fizzes with everything you mix it with
- Yeast smells like bread and is the only tan powder
- Gelatin swells in water and is the only one to do that
- Ascorbic acid (Vitamin C) is the only acidic powder
- Salt has the only square grains
Keep in mind, pH is the negative log of H+ concentration, which means the more sample you add for the same amount of water, the further your pH will be from neutral (7). It is recommended that you make your own chart of test results and then check that against information found online, but this is especially important for pH.
Pay attention to what the powder looks like. If you practice a lot and learn to identify certain powders on sight, you don't need to run any tests on it and it will save a lot of time.
|Lemon Juice||Cloudy, yellowish||~2-3||citrus||none||C6H8O7||expect pulp|
|Rubbing Alcohol||clear||~6||sweet, similar to alcohol||none||C3H8O||slightly sweet smelling|
|Ammonia||Cloudy, especially after shaking||~10-11||pungent||none||NH3||expect it to be some random color and scent|
|Vinegar||clear||~2-3||sour||none||CH3COOH||very strong scent|
|Water||clear||~7||none||none||H2O||nothing special about it|
|Hydrogen Peroxide||clear||~6||none||tiny delayed bubbles||H2O2||delayed reaction in iodine, bubbles of oxygen appear when shaken|
Each liquid has a "give-away", making them fairly easy to identify-
- Lemon Juice has a strong lemon odor (and is a strong acid, like vinegar)
- Ammonia is the only strong base
- It is best to use pH paper first, before smelling the unknown liquid, so that you will never have to smell ammonia (even if by wafting) since it can be chosen conclusively if the unknown liquid has a very basic pH.
- Vinegar has a distinctive vinegar odor (and is a strong acid, like lemon juice)
- Rubbing Alcohol is neutral, but has a distinctive odor
- Hydrogen Peroxide and water are very similar (both are odorless, neutral liquids), but there is a simple way to tell them apart. Fill a small well in your testing tray with the liquid, put in a few drops of iodine and stir. After about a minute (though sometimes more), tons of bubbles will appear if it is hydrogen peroxide, while nothing will happen in water (besides the color change due to iodine's color).
|Aluminum||gray||light||none||little fizz||no||Al||delayed reaction with HCl|
|Copper||copper||heavy||none||none||no||Cu||very easy to ID|
|Iron||black||heavy||none||fizz||yes||Fe||delayed reaction with HCl and smells bad, almost like rotten eggs|
|Tin||gray||light||none||little fizz||no||Sn||yellow tint|
|Magnesium||gray||light||little||fizzes and loses color; dissolves after a while||no||Mg||dull|
Almost every metal has a "give-away", making them fairly easy to identify-
- Iron is the only magnetic metal
- Copper is the only metal with a color other than grey (or similar).
- Magnesium will often steam with HCl, and will also let off a strong odor when HCl is added.
- Zinc will react vigorously (but will not steam) with HCl, and is non-magnetic.
- Tin and aluminum are very similar (neither react very much with HCl), but there are a few things that can be done to tell them apart. First, tin often has a yellowish tint, which aluminum will never have. Next, tin is often fairly shiny, while aluminum is dull. Lastly, if the metal is very malleable, it is probably aluminum (think aluminum foil).
In Crime Busters, there are 3 nonmetals which can never be mixed in the event: yeast, vitamin C, and sodium acetate. Everything left is neutral or basic and non-biological.
The key to finding the components to a mixture is to react each off individually. If there appears to be a powder and a crystalline component, add HCl or iodine to a sample. If the iodine turns blue, finding the first component will be straightforward because you will only need to find the pH of the mixture with water. A more neutral pH will mean that the noncrystalline component is flour; a more basic pH will mean cornstarch. If the iodine fizzes (and the HCl), then the component is Alka-Seltzer. A fizz with only the HCl means the component is either CaCO3 or NaHCO3. Once again, a pH test will show the difference: a neutral pH means calcium carbonate, and a basic pH means baking soda. No reaction means gypsum. To find the crystal, test for solubility. Sand will not dissolve, whereas salt and sugar will. The difference between the latter two is that salt has cubic crystals, and sugar has irregular crystals.
Two crystals are fairly easy to separate because the HCl and iodine can be skipped, and only solubility needs to be tested. Once again, a component that does not dissolve is sand, and a component that does is either salt or sugar, which can be differentiated by crystal shape. If both dissolve, the mixture is salt and sugar (probably the single most common mixture in this event).
For two powders, test with iodine first, then HCl if not all of the mixture fizzed or turned blue, and finally pH if needed. Go off of the information above to find each, and use logic if two things react at once.
This is very easy to do but must be done with care. Place a dot of ink (solute) at one end of a strip of filter paper. Then, get a small cup of solvent (often dH2O) and put the paper on the cup just so that the ink dot is above the waterline. Wait for the colors to separate, and that's it! Once the colors have stabilized, remove the paper from the solvent, and quickly put a line in pencil where the top edge of the water is on the paper. This allows you to find the Rf (retention factor or retardation factor) value of any ink spot if it is included in a question.
For practicing paper chromatography at home, use a coffee filter paper or paper towel if you do not have chromatography paper. Alcohol-soluble markers and pens will not work if using water, and if they do, the results won't be very visible. Using water-soluble markers/pens like Expo Vis-a-Vis will get you the best results.
In paper chromatography, the paper is the stationary phase and the solvent is the mobile phase. The higher the Rf value, the higher the affinity the solute has for the mobile phase, and the lower the Rf value, the higher the affinity the solute has for the stationary phase.
Practice identifying and comparing fingerprints. There are 3 basic categories of fingerprints(arches, loops, and whorls). They are easily identified by there general shape and number of deltas (triangles made from ridges). Make sure you know if your event supervisor is looking for the basic type (loop, arch, whorl), or the more in-depth name (Tented Arch, Ulnar Loop, etc.).
- Arches= a hill shape with no deltas
- Tented arch= an arch with a sharp corner at the top point
- Plain arch= an arch with a more rounded top point
- Loops= a beanish shape with one delta
- Ulnar Loop= A loop pointing towards the pinky
- Radial Loop= A loop pointing towards the thumb
- Whorls= a circle-like shape with two or more deltas
- There are many sub-categories of whorls, such as (but not limited to)-
- Plain whorls
- Central Pocket
- Double loops
- Accidental whorls
- There are many sub-categories of whorls, such as (but not limited to)-
The polymers required for this event are PETE (1), HDPE (2), PVC (3), LDPE (4), PP (5), PS (6), and PMMA (7). HDPE, LDPE, and PP float in water while PETE, PVC, PS, and PMMA do not. This means that the first group has a density of less than one and the second group more than one.
The following method of identifying the polymers is based on the assumption that the supervisor will only provide a beaker of water. A more precise method can be used if you are provided with corn oil, a certain percent concentrated solution of hydrogen peroxide, and a certain percent concentrated solution of salt water.
Identifying the polymers in the first group is easy. HDPE and LDPE are translucent while PP is not. HDPE is relatively more translucent then LDPE. Identifying in the second group is also fairly simple. PS will SLOWLY drop down in water or half of the flecks will sink while the other will float. PVC is sometimes rubbery, but never transparent, while PETE and PMMA are always clear.
Natural fibers come from plants (cotton) or animals (wool). Manufactured fibers are synthetics like rayon, acetate, and polyester, which are made from long chains of molecules called polymers. To determine the shape and color of fibers from any of these fabrics, a microscopic examination is made.
Generally, the analysts get only a limited number of fibers to work with--sometimes only one. Whatever has been gathered from the crime scene is then compared against fibers from a suspect source, such as a car or home, and the fibers are laid side by side for visual inspection through a microscope.
The first step in fiber analysis is to compare color and diameter. If there is an agreement, then the analysis can go into another phase. Dyes can also be further analyzed with chromatography, which uses solvents to separate the dye's chemical constituents. Under a microscope, the analysts look for lengthwise striations or pits on a fiber's surface or unusual shapes.
In short, the fiber analysts compare the shape, dye content, size, chemical composition, and microscopic appearances, yet all of this is still about "class evidence". Even if fibers from two separate places can be matched via comparison, that does not mean they derive from the same source, and there is no fiber database that provides a probability of origin.
Here is a useful table that can help to identify common fibers used in competitions.
Competitors are asked to know the difference between human, cat, and dog hair for competition. Microscopes are most commonly used for this, so studying images of different hairs is good practice for this portion of the event. Below are some examples of the required hair - overall, it is relatively easy to tell them apart. Cat hair has a scaly outside (cuticle) similar to human hair, though the core (medulla) is more broken or even invisible in human hair. Conversely, dog hair has a very thick medulla.
|Type of Hair||Cat||Dog||Human|
Competitors may be asked to identify the velocity of a single blood spatter, or multiple. It also may be asked to find the direction of the impact of a blood drop, which comes from the direction of the tail of the drop. If the blood drops of a spatter are smaller in diameter, the velocity of the spatter is larger. A good practice for this is to ask students for the velocity of various images of blood spatters. Some examples are shown below.
|Velocity||Image||Diameter of Drops||Speed||Common Causes|
|Low||4 mm or more||≤ 5 feet/second||Nosebleeds, small cuts, etc.|
|Medium||2-4 mm||5-100 feet/second||Backstabbings, beatings, etc.|
|High||< 0.001 mm||> 100 feet/second||Gunshots, bombings, etc.|
Usually a murder from a crime scene would not occur because of a low-velocity spatter found at the site of the event. Medium-velocity spatters and high-velocity spatters, however unlike low-velocity spatters, are commonly found at an assassination where a bloodstain is found.
This section will be mostly be discussing more topics on general questions normally not related to the crime scene since a DNA section related to the crime scene on a test usually only has competitors match DNA (electropherograms, gel electrophoresis, PCR, et cetera) samples of one of the suspects to those found at the crime scene, which is quite simple by analyzing the images of each one.
DNA stands for deoxyribonucleic acid and makes up genes in the nucleus of cells. Humans have 23 gene pairs, 46 genes in total, half from each parent. These genes are found in living cells like your lung cells as an example but usually are not found in dead cells such as fingernails and hair besides the ones in your hair roots. Body fluids such as blood and saliva that contain cells also contain DNA. It is a nucleic acid, one of the four major types of macromolecules, and is shaped like a double-helix. Two biopolymers called polynucleotides make up this polymer, which comprises nucleotides. These nucleotides each have a nucleobase and a 2-deoxyribose sugar group linked to a phosphate group, forming a phosphate-deoxyribose backbone. The nucleobase can be either adenine, guanine, thymine, or cytosine, where adenine and guanine are the purines and the thymine and cytosine are the pyrimidines. Adenine pairs with thymine and guanine pairs with cytosine, where they bind through covalent (also referred to as hydrogen) bonds.
Soil is usually included on a test as an identification lab test for one or more soil samples, but general questions may also be asked about soil. The six main types of soil are peaty, loamy, sandy, clay, chalky, and silty. A method to identify soil types is identifying them by the color of the soil. A dark brown color signifies a loamy soil, a darker brown color (almost black) signifies a peaty soil, sandy soil has a color of that of sand but darkened quite a bit. Clay soil has a slightly lighter color than sandy soil, chalky soil has a color similar to that of limestone, and silty soil has a similar color to loamy soil, but a slightly lighter color.
The pH of a soil sample may also be asked on a test using a powder and a labeled container you can put the soil sample in that tells you the pH of the soil based on color code. The following values of pH of each soil type may not be fully accurate, so it is recommended that you don't use them on your note sheets and check first to see if you get a different result when pH testing. Sandy soil has a pH of about 4.5-5.5, silty soil also has a pH of about 4.5-5.5, clay soil ph of about 5.5-7.0, loamy soil has a pH of about 5.5-6.5, peaty soil has a pH of about 3.0-4.0, chalky soil has a pH of about 7.1 or above. The ideal pH of plant growth is about 6 to about 8.
Some of the following may be asked on a test.
- The diameter of silty, sandy, and clay soil from least to greatest is in the following order: clay, silty, and sandy.
- Loamy soil is a mixture of sandy, silty, and clay soil and contains lots of organic matter, making it nutrient-rich and good for plant growth.
- Peaty soil is acidic and very high in nutrients, but this can lead to the soil having fewer nutrients ultimately.
Shoeprints and Tire Tracks
These two topics are mostly matching using images of shoeprints and tire tracks, similar to some of the other topics in this event, however, the type of print may be asked. There are three types of prints: patent (also called visible), plastic, and latent. A patent print is one that is already visible to the human eye, such as a print from water or blood on the ground. Like a patent print, plastic prints are also visible when made, except that an imprint is made in the ground itself, a force is exerted on the ground by the shoe that causes the ground beneath the shoe to decrease a little in elevation, usually on a surface as mud or clay with high moisture, whereas patent prints just contact between the ground and the shoe, forming a print mark resembling the shoe from a substance that is visible. Latent prints are not visible and therefore need different kinds of methods depending on the print to uncover them so that they are visible. These methods are more explained in-depth at the Forensics page, where you can find a few examples.
Water Testing (Not part of 2015 event)
The rules describing water testing are very vague. They only specify what can be tested for, but not how they can be tested. Titrations, probes, and colored strips are some possible methods used. Below is a table of the very basics on each of the aspects included in water testing.
Examples of Water Testing on Past Tests
Keep in mind that this portion of the event is worth 25% of the score. So, it is very important to leave enough time to get it done right!
An event supervisor will likely give few instructions besides something along the lines of: "Based on your analysis of the evidence, who is likely the culprit?" However, there are many things that they may be looking for beyond just a name-
- Rationale based on physical evidence- Use the evidence to support your claim. Talk about every piece of physical evidence that points to that person. To connect someone to the crime scene, one could cite a connection like "Joe works with flour daily, and flour was found at the crime scene" or even more simply "Joe's fingerprints were found at the crime scene".
- Reasons why it wasn't the other suspects- Even if the test does not explicitly ask for this, it is an excellent idea to include it in the essay. Write at least a sentence for each person (more than a sentence if there is a lot evidence pointing towards them and you have to explain more in-depth why it wasn't them). If there is a lot of evidence against a second person, but you're sure it wasn't them, then talk about a logical reason why there would be all of that evidence (for instance, "they work at the crime scene" is a common reason). Also, even if someone has no evidence against them, include that in the essay: "Joe had no evidence connecting him to the crime scene, so he was not the culprit".
- Motives- Give a motive for the person suspected to be the culprit, or if the proctor gave possible motives in the bios, restate them. This can add a lot to the essay, and help support your claim even if the wrong person has been selected.
- Multiple or No Culprits from List of Suspects- While most tests will have one culprit from the list of suspects, do not get trapped into thinking that it must be only one person. Some proctors may set up the test to point to two people working together, or they may leave insufficient evidence to point to anyone. If either is the case, adjust the essay structure to fit the claim, and make a logical explanation. If correct, you will likely do very well. If incorrect, a logical explanation should receive a decent amount of credit for the essay anyway to still allow for a high placing.
- Essay Structure-This can never hurt to have and takes very little time to do. Having a planned structure can also save time when planning the essay during the event. A simple, yet effective structure goes as follows.
- Intro Sentence- i.e. "Based on the evidence gathered, we concluded that the culprit was Joe".
- Lead-in to evidence- i.e. "There is much evidence to support our conclusion"
- State evidence in multiple sentences- i.e. "Flour was found at the crime scene, and Joe works with flour daily. Also, Joe's fingerprints and DNA were found at the crime scene. Finally, Joe.... etc."
- Lead-in to other suspects- i.e. "In addition, there was not enough evidence to point to any of the other suspects"
- Sentence on each suspect- See "Reasons why it wasn't the other suspects" section above
- Conclusion Sentence- i.e. "Therefore, it can be concluded that Joe was the culprit."
Multiple Short Essays
With the time crunch often imposed on the scorers, a sequence of shorter essays (50 words or less) may sometimes be asked as the analysis. These typically address specific areas of the analysis: something about the crime, how it was committed, who committed it, the sequence of events, or something else of that sort.
At the Competition
Once materials are given to teams and the supervisor starts the competition, start by doing the paper chromatography test. Then, look at the rest of the test and estimate how long it will take or how much there is to do. If it is a lot, make sure to split up the work in order to avoid having wasted potential and then not finish. While the chromatography is going, identify all the unknowns using the tests described above. Please note that at higher levels of the tournament (state, national) and even sometimes Regionals, different compounds may be combined with each other- for example, flour and Alka-Seltzer. While one person is testing unknowns, the other might want to do the fiber, hair, or polymer testing. If there is a microscope set up for the hairs, make sure to go there first, because it will get crowded near the end, when teams may have to waste time waiting. After all the unknowns are identified, read through the packet to learn about the crime scene, and answer the questions. Then, after questions have been answered, write out the crime solution essay, discussing how the team chose the culprit(s), based on their motive and supporting evidence (the unknowns the person was carrying compared to the substances found at the crime scene). Following the supervisor's instructions, hand in the test and answers, clean up your lab area and relax until the supervisor dismisses the teams.
Make sure to leave enough time for the essay. Depending on the event, it may be simple or extremely complex; the National supervisor for this year has a tendency to write events with complex essays that require a fair amount of time to write.
WARNING: The rules say teams will get 50 minutes. However, the 50 includes the supervisor talking about safety/tips/rules/etc, so often teams will only have 40-45 minutes to actually work. It is probably a good idea to practice with only 40-45 minutes to get used to competition conditions. At 2010 Nationals, a brief introduction was given, then 45 minutes to work, along with a 5 or 10 minute clean-up time after teams handed in their tests.
HINT: In some competitions, teams may not get full points for ONLY identifying the substance. In many instances, teams will be given a blank chart that must be filled in with observations. These observations may include (but are not limited to): HCl test reactions, Iodine test reactions, pH, Solubility in water, Shape, Size, or Color. Even though with one simple HCl and water test, one could figure out Alka-Seltzer, taking time to test it or write down all observations could help. Even if you skip a small portion, such as hairs, placing is still possible if all observations were written down, and not just the identity of the substance, seeing as the identification and process of identifying the substance is worth 50% of the points. Some supervisors will even put a scoring chart on the front/back of the handout/packet to show the breakdown of points. Even if you fail to correctly identify a substance, the supervisor could award partial credit for filling in observations.
The scoring is composed of these elements:
- Unknowns Identification (50% of total score) (Second Tiebreaker)
- Chromatography (5%)
- Polymer Testing/Natural and Man-Made Substances (Replaced Water Testing) (10%) (Third Tiebreaker)
- DNA, fingerprinting, tire treads, fingerprints, shoe prints (10%)
- Crime Solution Essay (25%) (First Tiebreaker)
- Note: You will need to print off the fingerprints, shoeprints, and DNA yourself for the following tests.