Crime Busters

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Crime Busters
Chemistry & Lab Event
Forum Threads 2014 2013 2012
2011 2010 2009
Tests 2014 2013 2012
2011 2010 2009
There are no images available for this event
There are no question marathons for this event
Division B Champion Meads Mill Middle School
This event was not held last year 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.

Contents

Supplies

Every team must bring these safety items to be allowed to participate.

  • Lab aprons or lab coats. If you're using lab aprons, make sure you're wearing long sleeves that reach the wrists.
  • Closed toe shoes, NO sandals
  • Pants or skirts that cover the legs to the ankles
  • Indirect vent Goggles (ANSI Z87)(eye protection #4)

Also, the team should and may have the following:

  • One 8.5" x 11" two-sided page of notes per student (see Note Sheets for help)
  • Writing instruments(pencils!)
  • Paper towels
  • Magnets
  • Microscope slides and cover slips
  • Tweezers or forceps
  • pH paper
  • Hand lenses
  • Test tubes and racks, spot plates, well plates, reaction plates or similar small containers for mixing
  • Something for scooping and stirring

The supervisor will provide everything else you need, so if you bring anything outside of what the rules allow you will be penalized.

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
    • Sugar
    • Flour
    • Cornstarch
    • Gypsum
    • Baking Soda
    • Powdered Gelatin
    • Powdered Alka-Seltzer
    • Sodium Acetate
    • Vitamin C
    • Yeast
  • Metals
    • Aluminum
    • Copper
    • Iron
    • Tin
    • Zinc
    • Magnesium
  • Liquids
    • Rubbing Alcohol
    • Household Ammonia
    • Water
    • Vinegar
    • 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. If you can do this, it helps very much when it comes time for the competition.

Water Testing

- Water Testing (Not part of 2014 event)


Charts

Powders

Powder Crystal Shape Color Solubility pH HCl Iodine Notes
Sodium Acetate powder - irregular shape white yes 9 none none endothermic and has a distinctive sweet odor
Sand random white no 7 none none; bad odor does nothing, may have black specks
Calcium Carbonate powder white no 7 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 7 none blackens it - iodine clumps together, unlike cornstarch Clumps with water
Cornstarch powder white no - forms solid-liquid substance 7 none blackens it pure white, feels slippery
Gelatin grains tan no; turns into gel 7 none none swells in water
Alka-Seltzer powder white yes 9 fizz fizz fizzes with everything
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 9 extremely fizzy for a long while none; more red-brown than Plaster of Paris rough texture (kinda)
Gypsum powder white no 7 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

Liquids

Liquid Color pH Scent Iodine Notes
Lemon Juice clear 3 citrus none expect pulp
Rubbing Alcohol clear 7 alcohol none slightly sweet smelling
Ammonia clear 11 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 7 none fizz delayed reaction

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).

Metals

Metal Color Density Water HCl Magnetic Notes
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
Zinc gray heavy none fizz no shiny
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).

Chromatography

This is very easy to do but must be done with care. You put 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 you have taken the paper out, 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 they ask, or they might be looking for it for full credit.


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.

Fingerprints

Some of the basic fingerprint patterns

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

Polymers

You have to know PETE (1), HDPE (2), PVC (3), LDPE (4), PP (5),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.

Fiber Analysis

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.

Analysis

Keep in mind that this portion of the event is worth 25% of your score. So, ALWAYS, ALWAYS save enough time for you to get it done right!

There are two common ways that an event supervisor could approach the analysis portion of the test-

Essay

They 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- You must 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, you would see 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 they do not explicitly ask for this, it is an excellent idea to include it in your essay. Write about 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, say that in your essay: "Joe had no evidence connecting him to the crime scene, so he was not the culprit".

Motives- Give a motive for the person you suspect to be the culprit, or if the proctor gave you possible motives in the bios, restate them. This can add a lot to your essay, and help support your claim even if you have the wrong person.

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 your essay structure to fit your claim and make a logical explanation. If correct, you will likely do very well. If incorrect, a logical explanation should get you a decent amount of credit for the essay anyway.

Essay Structure-This can never hurt to have, and takes very little time to do. 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) are asked addressing specific areas of 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 you get your materials and the supervisor starts the competition, start by getting your chromatography paper started. Then, look at the test and see how long you think it will take or how much there is to do. If it is a lot, make sure you split up the work because you don't want to have wasted potential and then not finish. While the chromatography is going, identify all the unknowns using tests (see section 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 you go there first, because it will get crowded near the end, and you may have to waste time waiting. After all the unknowns are identified, read through your 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 your papers, clean up your lab area, and relax until the supervisor dismisses you.

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 you will get 50 minutes. However, the 50 includes the supervisor talking to you about safety/tips/rules/etc, so often you will only have 40-45 minutes to 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 you had handed in your test.

HINT: In some competitions, you may not get full points for ONLY identifying the substance. In many instances, they will hand you a blank chart that you must fill your observations into. 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, you could figure out alka seltzer, taking time to test it or write down all observations could help you. Even if you skip a small portion, such as hairs, you can still place if you write down all the observations, and not just the identity of the substance, seeing as the identification and process of identifying the substance is worth 50% of your points. Some supervisors will even put a scoring chart on the front/back of the handout/packet that you are given to show you the breakup of points. Even if you fail to correctly identify a substance, the supervisor could give you partial credit for filling in observations.

Scoring

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)

Practice Tests

  • Note: You will need to print off the fingerprints, shoeprints, and DNA yourself for the following tests.

"Dwisney Stars-Twenty Years Later" Test

"Dwisney Stars-Twenty Years Later" Answer Key

2009 Northridge Invitational Test

2009 Northridge Invitational Answers

Smorgan6's Practice Test

Smorgan6's Practice Test Key