|Chemistry & Lab Event|
|Test Exchange Archive|
|There are no images available for this event|
|Division B Champion||Longfellow Middle School|
|This event was not held recently in Division C|
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 Water Testing
- 10 Analysis
- 11 At the Competition
- 12 Scoring
- 13 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.
|Sodium Acetate||powder - irregular shape||white||yes||8||none||none||endothermic and has a distinctive sweet odor|
|Sand||random||white||no||6||none||none; bad odor||does nothing, may have black specks|
|Calcium Carbonate||powder||white||no||6||fizz||none; the color looks sort of like mustard/peanut butter||the powder it self is very airy and hole-y|
|Vitamin C||grains||white||yes||2||none||clears it||may have a colored tint- green, yellow, pink, orange (if from tablets). Distinctive smell.|
|Salt||signature square grains||white||yes||7||none||none||delayed reaction with iodine (may be difficult to observe)|
|Sugar||grains||white||yes||7||none||none||Similar to salt but grains are slightly rounded|
|Flour||powder||Off-white||no; lumpy||6||none||blackens it - iodine clumps together, unlike cornstarch||Clumps with water|
|Cornstarch||powder||white||no - forms solid-liquid substance||8||none||blackens it||pure white, feels slippery|
|Gelatin||grains||tan||no; turns into gel||6||none||none||swells in water|
|Alka-Seltzer||powder||white||yes||6||fizz||fizz||fizzes with everything including water|
|Yeast||pellets||tan||no||7||none||none||generally easy to identify since it smells sort of like bread most of the time|
|Baking Soda||powder||white||yes||8||extremely fizzy for a long while||none; more red-brown than Plaster of Paris||rough texture (kinda)|
|Gypsum||powder||white||no||6||none||none||hardens in water|
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
|Lemon Juice||Cloudy, yellowish||2||citrus||none||expect pulp|
|Rubbing Alcohol||clear||6||alcohol||none||slightly sweet smelling|
|Ammonia||Cloudy, especially after shaking||10||pungent||none||expect it to be some random color and scent|
|Vinegar||clear||2||sour||none||very strong scent|
|Water||clear||7||none||none||nothing special about it|
|Hydrogen Peroxide||clear||6||none||fizz||delayed reaction|
|Bleach||Slightly yellowish tinge||8||Sharp, chlorine|
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||delayed reaction with HCl|
|Copper||copper||heavy||none||none||no||very easy to ID|
|Iron||black||heavy||none||fizz||yes||delayed reaction with HCl and smells bad, almost like rotten eggs|
|Tin||gray||light||none||little fizz||no||yellow tint|
|Magnesium||gray||light||little||fizzes and loses color; dissolves after a while||no||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 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 water line. 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) value of any ink spot if it is included in a question.
For practicing paper chromatography at home, use coffee filter paper or paper towel if you do not have chromatography paper. Alcohol-soluble markers and pens will not work, 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.
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), and PS (6). HDPE, LDPE, and PP float in water while PETE, PVC, and PS do not. This means that the first group has a density less then one and the second group more then 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 is 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 gets 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 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 looks for lengthwise striations or pits on a fiber's surface, or unusual shapes.
In short, the fiber analysts compares 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 you identify common fibers used in competitions.
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, 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 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%)
- DNA, finger printing, tire treads, finger prints, 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.