Science Crime Busters

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Science Crime Busters Event Links
Forum Thread: 2009 2010
Test Exchange: 2009 2010


Contents

Description

Students will identify perpetrators of a certain crime by identifying unknown powders, liquids, and metals, and analyzing shoe prints, tire treads, paper chromatography, and fingerprints. Students should be able to use this data to answer some questions about who committed the crime and how the evidence supports their argument.

Survival Kit

Every team must bring a bunch of stuff in order just to get into the testing room. The team must have:

  • Lab aprons or coats. If lab aprons, make sure you're wearing long sleeves.
    • Also, make sure you have closed toe shoes, NO sandals
  • Splash Goggles
  • Pencils (NOT PENS, you will most likely make mistakes)

Also, the team should have the following:

  • Standard sheet of paper (both sides) with notes on anything involved with the event! Only one sheet of notes (typed or handwritten) is allowed per team.
  • Extra pencil for chromatography
  • Paper Towels
  • Magnet
  • Microscope Slides
  • Testing trays
  • PH paper
  • Wood Splints (Make sure you have extra)
  • Some form of scoop for the powders

The supervisor will provide everything else you need, so if you bring it 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 3M HCl (hydrochloric acid)
  • a dropper bottle of Iodine
  • pH or Litmus paper
  • 15-20 unknowns
  • a container of water (with eye dropper)
  • 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.

Charts

Powders

Powder Crystal Shape Color Solubility pH HCl Iodine Notes
Sodium Acetate powder white yes 9 none none it kinda clumps in water
Sand random white no 7 none none does nothing, may have black specks
Calcium Carbonate powder white no 7 fizz none the powder it self is very airy and hole-y
Vitamin C grains white yes 7 none clears it may have a colored tint- green, yellow, pink, orange (if from tablets). Distinctive smell.
Salt grains white yes 7 fizz clears it 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 7 none blackens it Clumps with water
Cornstarch powder white no 7 none blackens it pure white, feels slippery
Gelatin grains tan no 7 none none gels water
Alka-Seltzer powder white yes 9 fizz fizz fizzes with EVERYTHING
Yeast pellets tan no 7 none none generally easy to identify
Baking Soda powder white yes 9 fizz none rough texture (kinda)
Gypsum powder white no 7 none none hardens water

Liquids

Liquid Color pH Scent Iodine Notes
Lemon Juice clear 3 citrus none expect pulp
Rubbing Alcohol clear 7 alcoholy none kinda sweet smelling
Ammonia clear 9 sweet 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 liquids has a "give-away", making them fairly easy to identify-

  • Lemon Juice has a strong lemony 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 Alcohal 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 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
Tin gray light none little no yellow tint
Zinc gray heavy none fizz no shiny
Magnesium gray light little fizz 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).

Water Testing

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 things that they can ask about and have you test for-

Measurement Units Low Mid-range High Description
Temperature #° Celcius Below 20° C 20-25° C (Room temp) Above 25° C Measure of heat
pH pH units 0-6.9 (Acid) ~7 (Neutral) 7.1-14 (Base) Measure of acidity/alkalinity
Hardness Parts per million (ppm) 0-140 ppm (soft water) 140-320 ppm (slightly to moderately hard water) More than 320 (very hard water) Measure of the amount of Sodium and Magnesium ions
Dissolved Oxygen (DO) Parts per million (ppm) 0-5 ppm (dangerous for fish) 6-8 ppm (habitable conditions) Above 9 (Very good for fish to flourish) Measure of the amount of gaseous oxygen (O2) dissolved
Biochemical/Biological Oxygen Demand (BOD) Milligrams per liter (mg/L) 1 mg/L (Pristine river) 2-8 mg/L (Moderately polluted river) 20;200 mg/L (Treated;Untreated Sewage) Measure of the quantity of the dissolved oxygen used by bacteria as they break down organic wastes
Chemical Oxygen Demand (COD)  ?  ?  ?  ? Measure of the capacity of water to consume oxygen during the decomposition of organic matter and the oxidation of inorganic chemicals
Turbidity Nephelometric Turbidity Unit (NTU) Less than 1 NTU (Ideal Drinking water) 1-5 NTU (Potable water) Above 5 NTU (Non-potable water) Measure of the degree to which the water looses its transparency due to the presence of suspended particulates
Common Cations Depends on test Depends on test Depends on test Depends on test "Common Cations" is a broad range of things with atoms that have lost an electron to become positively charged
Common Anions Depends on test Depends on test Depends on test Depends on test "Common Anions" is a broad range of things with atoms that have gained an electron to become negatively charged
Conductivity/Total Dissolved Solids (TDS) Parts per million (ppm) 0-140 ppm (Ideal drinking water) 140-400 ppm (Average tap water) Above 500 (Non-potable water) Measure of the ability of water to pass a current

Examples of Water Testing on Past Tests

2010 Southeast Pennsylvania Regionals- A few strips were given, very similar to pH paper, that you just dipped in and compared to a chart that they provided. You then had to match you data (the crime scene liquid) to data provided for the liquids that the suspects were carrying (their water bottles) and say which it came from. There were 4 strips (so 4 tests total), similar to these- http://www.omega.com/pptst/WTS_Series.html. All in all, it wouldn't take you more than 5 minutes max.

2010 Pennsylvania States- Four liquids were given at a shared station, and you had to do two tests on each: pH and some sort of titration (so 8 tests total). For the pH portion, I think it was done using indicator dyes, though I have almost no clue, because they said we could use pH paper instead if we wanted. As far as the titration, they had someone there to explain how to do it, and written instructions. You filled a container with the liquid, then added a certain number of drops of an indicator and a certain number of drops of another chemical, mixing continuously. You then had a tiny syringe filled with another chemical and you slowly added it, mixing constantly until the solution turned purple (it was pink beforehand). I was terrible at this, so it took me around 20 minutes, but you could probably have done it in 10 if you had done a titration before (I would recommend practicing this at least once, because it seems like something that they give at a fair number of competitions).

2010 Nationals- Basically, you got four probes (conductivity, DO, pH, and temperature) and a TI graphing calculator (already set up to receive and display information from any probe if you plugged it in. No preparation was needed to understand how it worked, since they gave written and verbal instructions). You then had an observation/conclusion sheet to record information. You wrote down the probe used and the numerical value received (0.5 points for each one of these pairs) and then had a line to write a conclusion based on the information (0.5 points for each of these). To get full credit (5 points), you needed 5 data entries and 5 conclusions based off those entries. Here is what we had (I don't remember the numbers)-

DO- ### (low)- There is very little dissolved oxygen in the liquid

Temperature- ### (room temp.)- The liquid is about room temperature

Conductivity- ### (high)- The liquid conducts electricity very strongly

pH- ##.# (high)- The liquid is very basic

Temperature- ### (same as first entry)- the liquid does not change temperature over time

  • I'm not sure if the last one was what they wanted, but there were only 4 probes and you needed 5 tests, so we put that down.

On the crime part of the test, they said "Liquid S (the one you tested) was found around the area of a freezer, dishwasher, and sink (or something to this extent). Do the necessary tests to figure out exactly where it came from". Since it was very basic and a strong conductor, we said it was from the freezing coils in the freezer (again, I don't know for sure if that's right). They didn't ask any supplemental questions about water testing, like they do for the powders, liquids, fingerprinting, DNA, etc.

Chromatography

This is very easy to do. You put a dot of ink on a 6" by 1" piece of white construction paper. Then, get a small cup of water 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, ot they might be looking for it for full credit.

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 deltas
    • There are many sub-categories of whorls, such as (but not limited to)-
      • Plain whorls (most important to know; sometimes simply referred to as "whorl")
      • Double loops
      • Accidental whorls
      • Tracings
    • It is highly unlikely that they will ask for one of these, so this should be the last thing you should worry about learning. However, the most important whorls to know are the plain whorl and double loop.

Polymers

Polymers (Not part of 2010 event)


Analysis

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

Essay (Large Majority of Tests)

By far the most common way that the analysis will be set up is in an essay form. 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 scence" 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, then 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. "Also, 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."

Short Answer Questions (2007-2010 Nationals tests, among others)

This setup is less common at the Regional and State level, but has been the setup on the last four Nationals tests. It will consist of a few short answer questions asking you to explain something about the crime, how it was committed, who committed it, or something else of that sort. That being said, it is much easier to answer this type of question well with little practice, as opposed to essays, which take much practice to get full credit.

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) 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 water testing. If there is water testing at a common station, 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.

Scoring

The scoring is composed of these elements:

  • Unknowns Identification (50% of total score)
  • Chromatography (5%)
  • Water Testing (10%)
  • DNA, finger printing, tire treads, finger prints, shoe prints (10%)
  • Crime Solution Essay (25%) (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

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