Forensics C

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Re: Forensics C

Postby YungMihi » April 9th, 2018, 1:31 pm

Hey anyone have any good resources for soil id, pollen, and ento? These topics haven't really come up in the states or regionals tests but I feel like they will at Nats.

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Re: Forensics C

Postby ET2020 » April 16th, 2018, 11:44 am

Can someone please clarify what concentrations of liquids will be used? The rules just say "10% NaCl, 46% isopropyl alcohol" etc without specifying whether it is percent by mass or volume. Also many of the old nationals test provide solution concentration and density, but their numbers don't make sense to me. For example one test says "46% isopropyl alcohol: 0.95 g/cm^3). The problem is that 46% iso by mass has a density of 0.88, while by volume has a density of 0.90. Does anybody know if we can get clarification on this?
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Re: Forensics C

Postby pikachu4919 » April 16th, 2018, 12:06 pm

YungMihi wrote:Hey anyone have any good resources for soil id, pollen, and ento? These topics haven't really come up in the states or regionals tests but I feel like they will at Nats.


The wiki is a good start, and so is this (it's the national supervisor's website). From there, you could expand your own search, as that's a much more effective way to learn.

ET2020 wrote:Can someone please clarify what concentrations of liquids will be used? The rules just say "10% NaCl, 46% isopropyl alcohol" etc without specifying whether it is percent by mass or volume. Also many of the old nationals test provide solution concentration and density, but their numbers don't make sense to me. For example one test says "46% isopropyl alcohol: 0.95 g/cm^3). The problem is that 46% iso by mass has a density of 0.88, while by volume has a density of 0.90. Does anybody know if we can get clarification on this?


The recipes for those solutions are actually found here, and having used this before, I know for sure that it is not percent by mass lol. I'm not sure what system that's based on, but it is literally the national supervisor's recipes, so doesn't hurt to follow it, I guess.
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Re: Forensics C

Postby potatosoup9000 » May 8th, 2018, 4:51 pm

Does anyone know how Snell's law/index of refraction calculations were done at nationals? The seniors from our team never did them. Were they done normally, like shinning a laser through a flat sample, or do you have to do extra math for the spherical shape of the sample?
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Re: Forensics C

Postby sofossils » August 22nd, 2018, 8:30 am

Hello all! I am looking for a "portable" replacement to a Bunsen burner for flame tests. Does anyone have any suggestions for something that I could buy for my team? We do not have access to a chemistry lab on a regular basis, and using matches/candles did not work well! Any advice is welcome.
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Re: Forensics C

Postby pikachu4919 » August 22nd, 2018, 10:50 pm

potatosoup9000 wrote:Does anyone know how Snell's law/index of refraction calculations were done at nationals? The seniors from our team never did them. Were they done normally, like shinning a laser through a flat sample, or do you have to do extra math for the spherical shape of the sample?
Thanks!


Sorry, this is quite late, but I'm not entirely sure since I don't remember if glass was tested when I competed. I think you use the same solutions used for plastic density testing and rely on the rule that if the fluid and the glass have the same index of refraction, the glass will disappear in the solution. Other than that I'm not sure the national supervisor would even make you do a Snell's Law math problem, unless her tests have changed dramatically since my time.

sofossils wrote:Hello all! I am looking for a "portable" replacement to a Bunsen burner for flame tests. Does anyone have any suggestions for something that I could buy for my team? We do not have access to a chemistry lab on a regular basis, and using matches/candles did not work well! Any advice is welcome.


There are portable bunsen burners (you can get them on amazon apparently), and then another thing you could do would be alcohol burners (sometimes used as a substitute if the lab has no gas outlets but it's not ideal since its flame color is too close to that of sodium and it is not even close to generating as much heat as a real bunsen burner). If you plan to use it at competition, it's something I'm not entirely sure is the best idea - while it could technically count as something that could fit under the description in Rule 2.a.viii, not every ES will have the same interpretation of what stuff would be allowed under that rule (i.e. an ES may interpret it as something that's not on the list of the allowed equipment because it's not explicitly written itself despite the "etc." at the end). For example, candles technically could count under that rule, and we brought one and it got confiscated by the forensics staff at State (and my state is run by the national supervisor for the event). Plus, there *could be* hazards involved with transporting a portable burner because you'd need either MeOH, IPA, or butane (depending on what you use) to operate it, which are all flammable (I say "*could be*" since I'm not sure what your school administration's policies are on those kinds of matters).
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Re: Forensics C

Postby dholdgreve » August 23rd, 2018, 9:37 am

sofossils wrote:Hello all! I am looking for a "portable" replacement to a Bunsen burner for flame tests. Does anyone have any suggestions for something that I could buy for my team? We do not have access to a chemistry lab on a regular basis, and using matches/candles did not work well! Any advice is welcome.


Candles and alcohol burners tend to not be hot enough to get some chemicals to their flash point. For practice (only) consider using the short, fat propane cylinders used for camping lanterns, They have a large snap on base that will make them nearly impossible to tip. Then use screw on torch tip with an adjustable "throttle." The flame usually a transparent blue, so it doesn't mask the colors generated by the metals.
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Re: Forensics C

Postby pikachu4919 » August 23rd, 2018, 10:59 am

dholdgreve wrote:
sofossils wrote:Hello all! I am looking for a "portable" replacement to a Bunsen burner for flame tests. Does anyone have any suggestions for something that I could buy for my team? We do not have access to a chemistry lab on a regular basis, and using matches/candles did not work well! Any advice is welcome.


Candles and alcohol burners tend to not be hot enough to get some chemicals to their flash point. For practice (only) consider using the short, fat propane cylinders used for camping lanterns, They have a large snap on base that will make them nearly impossible to tip. Then use screw on torch tip with an adjustable "throttle." The flame usually a transparent blue, so it doesn't mask the colors generated by the metals.


Going off this, you could maybe try a butane burner as well. A lot of camp stove fuel packs have that, propane, or fuel that's propane/butane hybrid. I've never tried it personally so I'm not sure if I would encourage or discourage it, but it's an idea, especially if some other camp fuel types may work better than propane by itself.
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Nationals 2016 ~ 4th place Forensics


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Re: Forensics C

Postby sofossils » August 26th, 2018, 3:50 pm

Thanks for the feedback everyone!

I'll keep you posted on what works out.
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Re: Forensics C

Postby daydreamer0023 » August 29th, 2018, 6:14 pm

sofossils wrote:Thanks for the feedback everyone!

I'll keep you posted on what works out.


Kinda late here, but I've used this micro torch for practice before: https://www.amazon.com/Bernzomatic-ST25 ... B0000CBJBQ. It's worked fine for me and all you need is to get the butane that goes with it.
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Re: Forensics C

Postby simonsilverpor » September 3rd, 2018, 7:27 am

cool


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