Forensics C

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Forensics C

Postby Jim_R » August 10th, 2014, 10:46 am

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Re: Forensics C

Postby samlan16 » September 23rd, 2014, 4:49 am

Opinions on the binder? I'm surprised they upgraded us from a sheet, but it will probably make Forensics a ton harder. :|
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Re: Forensics C

Postby JonB » September 23rd, 2014, 5:15 am

samlan16 wrote:Opinions on the binder? I'm surprised they upgraded us from a sheet, but it will probably make Forensics a ton harder. :|



Depends on the test. If it is a short test, then a binder could be a huge help. On a long test, it will hold you back. Look at the history of the event at your specific competition to see what would be best, but never depend on the binder- it should be a reference of last resort.

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Re: Forensics C

Postby iwonder » September 23rd, 2014, 7:28 am

Last year when we had two sheets of paper me and my partner actually struggled to fill them up. I'm honestly not sure what you'd do with a binder. I mean, we didn't have certain information that we should have (mostly the trivia style questions), but we had the space for it if we had accounted for the random stuff before the contest. Personally, I would just bring a sheet or two, maybe three, with everything nicely organized. I think a binder is just going to slow you down, even it's well organized (also, space constraints).
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Re: Forensics C

Postby pikachu4919 » September 24th, 2014, 6:03 pm

I was also really surprised when I saw the change to a binder because I did Forensics when only one sheet was allowed, and I managed to fit everything I needed on that one sheet (with small font :lol: but still...one sheet). The only thing I can think of right now that might require more than a sheet of notes is probably mass spec...I'm sure there are other things too, but that's all I can think of now...
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Re: Forensics C

Postby jdjmoon » November 6th, 2014, 7:30 am

Does anyone have good site for Mass Spectroscopy? I had one, but now it is unavailable, so I cannot get any good informations on it.

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Re: Forensics C

Postby computergeek3 » November 9th, 2014, 1:52 pm

jdjmoon wrote:Does anyone have good site for Mass Spectroscopy? I had one, but now it is unavailable, so I cannot get any good informations on it.

http://ochem.jsd.claremont.edu/

You might have to dig around on here a little bit, but Mass Spec is there and explained pretty well.
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Re: Forensics C

Postby byi » November 11th, 2014, 4:16 pm

CAN ANYONE HELP ME WITH A FORENSICS ASSIGNMENT?

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Re: Forensics C

Postby bernard » November 11th, 2014, 5:00 pm

byi wrote:CAN ANYONE HELP ME WITH A FORENSICS ASSIGNMENT?

If you want help, you will have to be more specific and perhaps also post the questions you need help with.
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Re: Forensics C

Postby elizagabito » December 12th, 2014, 12:33 pm

I need help... I don't know anything that deals with chemistry so I basically don't know anything about this event... Any suggestions on what to study first? Like what are good sites & techniques on studying.

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Re: Forensics C

Postby samlan16 » December 18th, 2014, 10:57 am

elizagabito wrote:I need help... I don't know anything that deals with chemistry so I basically don't know anything about this event... Any suggestions on what to study first? Like what are good sites & techniques on studying.

The best way to study for Crime Busters or Forensics is to get your hands on the permitted compounds and run tests on them all before the competition. You learn the lab techniques this way, and if you come across something you don't entirely understand, you can look it up. But start by learning the qualitative stuff first, then learn why it happens. (Also, the chem that you will see on this test up to state is at most reading a mass spectra, IDing chemical structures, and doing a little stoichiometry. Don't be too concerned if it doesn't come easily.)
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Re: Forensics C

Postby Azismith » December 30th, 2014, 12:47 pm

I was wondering -- does anyone have a good way (other than the super-subjective 'which bends easier? which scratches easier?) to differentiate between PC and PMMA? Thanks! :)

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Re: Forensics C

Postby samlan16 » December 31st, 2014, 1:59 pm

Azismith wrote:I was wondering -- does anyone have a good way (other than the super-subjective 'which bends easier? which scratches easier?) to differentiate between PC and PMMA? Thanks! :)

Density. PC is somewhere between 1.2 and 1.6 g/mL, but PMMA is around 1.16 g/mL. If you are incredibly lucky, they will give you corn syrup to test this in. PMMA floats; PC sinks.
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Re: Forensics C

Postby sciencegeek999 » January 4th, 2015, 1:46 pm

Hey guys, I got put in this event, and I've never done it before. Other than the rules, what should I know about it to start off? How do I prepare for it? Thanks in advance.

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Re: Forensics C

Postby pikachu4919 » January 4th, 2015, 4:51 pm

samlan16 wrote:
Azismith wrote:I was wondering -- does anyone have a good way (other than the super-subjective 'which bends easier? which scratches easier?) to differentiate between PC and PMMA? Thanks! :)

Density. PC is somewhere between 1.2 and 1.6 g/mL, but PMMA is around 1.16 g/mL. If you are incredibly lucky, they will give you corn syrup to test this in. PMMA floats; PC sinks.


25% NaCl solution should also work since its density is ~1.19 g/ml. The Woz (national forensics supervisor but she also supervises in my state) uses this for that reason.

sciencegeek999 wrote:Hey guys, I got put in this event, and I've never done it before. Other than the rules, what should I know about it to start off? How do I prepare for it? Thanks in advance.


Here's a really good post from a past year's forum for this:

salcedam wrote:What I would recommend is starting right off the bat with learning how to identify the powders since that's a major chunk of the test and subsequently, one of the more important parts of it. For powders, you should have some sort of flowchart in place so as you can sequentially go through different tests (such as solubility, flame colors, HCl reactions, etc.) until you can identify it. For example, to identify boric acid, the only test you need to do for that is to do a flame test because boric acid makes a green flame. LiCl gives off a red flame and KCl gives off a purple flame. Those are the only three powders that will give those distinctive colors. The others will either give you a yellow, orange-ish, or no flame color at all. That's when you need to continue with the next step which would be to determine solubility and so on and so forth.

Then once you have powders down or at least have an idea of how to do them, move to the fibers and plastics and learning to identify those using burn tests (for the fibers in particular since they usually won't allow burn tests for plastics). For plastics, you identify them using densities so you need a flowchart just like for the powders of what to do when one plastic sinks in one solution. So let's say you have a plastic that sinks in water. You know that it must have a higher density so then you test the density using salt water. Different competitions will give different concentrations so you should know the densities of the various concentrations of salt water so that when they give you, let's say, a 10% salt solution and it sinks, you know that it must have a density higher than 1.074 g/mL since that's the density of a 10% salt solution. Then you should test the plastic using corn syrup or some high density liquid to see if it floats or sinks. If it sinks in corn syrup, it has to be PVC (according to the flowchart I've made) and if it floats, it's PETE.

So basically, you need to research flowcharts on powders and plastics as well as learn specific characteristics of fibers such as how they react when burned and how they look. From powders, fibers, and plastics, you move on to everything else. I'd focus less on glass and dirt/tire tracks and such since that's mostly matching. Most tests that I've come across focus mainly on blood, fingerprints, reading mass spec, and the occasional entomology question. When studying those things, you don't need to get too in-depth, but you should go past the surface a little bit. I've had tests where they ask how fingerprints are formed, how many ridges a fingerprint has, things besides matching and identifying fingerprint types. Hope that helps somewhat!


I would add the following to this:
- flame tests can get easily ruined by sodium contamination, so they aren't always 100% reliable unlike solubility, in which it either dissolves or it doesn't and isn't very easily affected by contamination (that's what I recommend should be the first test to use on a flowchart)
- another more feasible difference between PVC and PETE is that PVC gives off a green flame (if provided by the supervisor since burning plastics is not allowed in competition). In fact, if it burns green, it will always be PVC since the other plastics don't give that color.
- glass isn't all matching--you also need to know how to interpret fracture patterns (I've seen questions like that before) aka determining which impacts came first/second, etc.

Be sure to check out the Forensics Wiki for info about important things to know, and feel free to PM me if you'd like since I've done this event for years.
Carmel HS (IN) '16
Purdue BiolE '20
Nationals 2016 ~ 4th place Forensics


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