Forensics C

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Re: Forensics C

Postby pikachu4919 » Fri Apr 21, 2017 2:26 pm

AllenWang314 wrote:For the Rfs of different molecules on nationals tests, the answer key usually just says things like 0.97, 0.55, 0.34, 0.24. Do they allow for a range of answers, so if I say 0.95, 0.59, 0.32, 0.22, will they accept that as valid, or will they only accept exactly what they have, can somebody with experience answer this?

Also, how does fluorescence work? Do we just take the gel-paper thing and shine a "flashlight"/blacklight at it? Are there two buttons on the blacklight for long and short wave length?


You definitely don't want to be off by too much but I would think so (then again they never return your nats tests so in reality you will never know).

And for your second question:

pikachu4919 wrote:
AllenWang314 wrote:Regarding national tests, what is fluorescence? What area (chromat, fibers, blood, or chem) of the event is it about? And what do we have to know about it, and what are websites that can give enough info?


The fluorescence is part of the TLC (thin layer chromat) you'll be doing on samples of different kinds of paints. iirc you perform the TLC on the paint and see if your sample will glow under different wavelength settings of a blacklight, and that's most of what you do.
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Re: Forensics C

Postby Abekitt » Sun Apr 23, 2017 6:15 pm

sciduck wrote:
18alia wrote:At regional, there were questions about the "medulla index" for each type of hair. As far as I can tell, they probably meant the medullary index, and this is not dependent on the type of hair. Does anyone know what the medullary index would be for each hair?
Also, does anyone know the index of refraction for types of glass? I know that for glass analysis, the glass dissapears in the liquid with the same index of refraction, but without knowing what kind of glass has that index of refraction, I'm not sure what I would do with that information, and I was asked to identify the type of glass at regional.


You can look up average/common medullary indexes. This was the first thing I got when I googled, but you should cross-check with other sources. http://www.aquinashs.org/ourpages/auto/2010/10/12/52283856/Medullary%20Index%20Information%201.ppt

For glass, I usually keep a chart of indexes for common things that show up. Again, google for them. Definitely know crown glass.

What kinds of glass do we need to know, is the list on the rule chart? Did you use a specific website for it, or did you just search the glass with the word refac index?
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Re: Forensics C

Postby sciduck » Mon Apr 24, 2017 3:35 am

Abekitt wrote:
sciduck wrote:
18alia wrote:At regional, there were questions about the "medulla index" for each type of hair. As far as I can tell, they probably meant the medullary index, and this is not dependent on the type of hair. Does anyone know what the medullary index would be for each hair?
Also, does anyone know the index of refraction for types of glass? I know that for glass analysis, the glass dissapears in the liquid with the same index of refraction, but without knowing what kind of glass has that index of refraction, I'm not sure what I would do with that information, and I was asked to identify the type of glass at regional.


You can look up average/common medullary indexes. This was the first thing I got when I googled, but you should cross-check with other sources. http://www.aquinashs.org/ourpages/auto/2010/10/12/52283856/Medullary%20Index%20Information%201.ppt

For glass, I usually keep a chart of indexes for common things that show up. Again, google for them. Definitely know crown glass.

What kinds of glass do we need to know, is the list on the rule chart? Did you use a specific website for it, or did you just search the glass with the word refac index?


I did the latter. I don't believe there is a list, I just looked at old tests to pick the important ones.
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Re: Forensics C

Postby 19sawickin » Sun Apr 30, 2017 5:12 pm

Did anyone take the Pennsylvania State Tournament Forensics test? It is always written by Harriton and is, in my opinion, by far the hardest test I have ever taken, national tests included. This year I believe there were 10 powders to test and 11 polymers, 5 of which were plastics that were easy enough to ID, the difficulty lying in the 6 different fabrics/hairs. Now, traditionally, I identify fabrics by burning them and observing their odors and how they react in the flames. I can also identify certain fabrics under a microscope, as long as they are natural fibers (is there anyway to distinguish synthetic ones from each other??). However, they only gave one tiny thread for each of the two fabrics, and single hairs that were even a challenge to find inside of the little bag that they were in. Furthermore, there were only two low-quality microscopes inside of the room for the 10 or so teams to share.

My question is, how can one possibly ID those hairs/fabrics if they didn't use a microscope? Is that even possible? Is it even the right strategy to try and identify the hairs under the microscope since it takes an exorbitant amount of time to place the hairs on the microscope slips and even locate them under the microscope? There was significantly more to the test than just ID-ing, so should I just skip the hairs???? I'm utterly confused, especially since I was using a microscope for an extended period of time, long enough to (unintentionally) prevent a team who placed from using the microscope (I'm fairly confident).

Anyone who took this PA test PLEASE help me understand how this test was "extremely easy."

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Re: Forensics C

Postby Magikarpmaster629 » Mon May 08, 2017 11:04 pm

So on the nationals website there are images of the rooms for every events except Forensics (here). Anyone involved in nats know if this is on purpose, or if someone just overlooked it?
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Re: Forensics C

Postby daydreamer0023 » Wed May 10, 2017 1:56 am

Anyone have a good way to distinguish nylon vs polyester?
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Re: Forensics C

Postby markuswso17 » Wed May 10, 2017 1:31 pm

daydreamer0023 wrote:Anyone have a good way to distinguish nylon vs polyester?


Under a microscope, Nylon looks like small clear rods. Polyester is the same thing but it isn't clear.
During burn test, Nylon curls when a few inches away form the flame while Polyester does not.
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Re: Forensics C

Postby pikachu4919 » Wed May 10, 2017 10:29 pm

markuswso17 wrote:
daydreamer0023 wrote:Anyone have a good way to distinguish nylon vs polyester?


Under a microscope, Nylon looks like small clear rods. Polyester is the same thing but it isn't clear.
During burn test, Nylon curls when a few inches away form the flame while Polyester does not.


You might also want to read up on the chemical makeups of each fiber, they can also tell you about chemical properties that the fibers might have (such as scent in the burn test, behavior during the burn test, etc.)

I think I know who both of you are and that you'll both be in this event at nationals, so here's a tip from me: The microscopes at nats aren't top-notch quality (believe me, I know) - sometimes, they might not really give you a good view of whatever you're looking at, and/or it is hard to quickly adjust the microscope to a good, focused view. That plus the fact that time flies so quickly at nats due to the sheer amount of stuff that the supervisor makes you do means that you possibly won't have that much time to do a microscope analysis if you're really really pressed - for me when I took this supervisor's exams, that's why I actually relied more on burn tests and my gut feelings/instinct for fiber and hair ID.
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Re: Forensics C

Postby KSSOISLIT » Sat May 13, 2017 6:30 pm

For the Nationals test, does the Woz set up slides with hair on microscopes, or do we have to prepare slides with hair they give us?
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Re: Forensics C

Postby KSSOISLIT » Sat May 13, 2017 10:57 pm

Another question, what would be the best way to distinguish between PP and LDPE as they behave similarly in most density tests and have similar appearances?
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Re: Forensics C

Postby pikachu4919 » Sun May 14, 2017 12:34 am

*caution - try not to double post

anyways....

KSSOISLIT wrote:For the Nationals test, does the Woz set up slides with hair on microscopes, or do we have to prepare slides with hair they give us?


It's DIY. You'd be really lucky to get a supervisor that would be willing to do such a thing for you.

KSSOISLIT wrote:Another question, what would be the best way to distinguish between PP and LDPE as they behave similarly in most density tests and have similar appearances?


Corn oil, which has a density of 0.91 g/cm^3, should work since PP's density is 0.90 g/cm^3 and LDPE's is 0.92 g/cm^3. It's really subtle but yeah. They additionally have different chemical monomers that might translate to differences in their overall properties but idk if they'd be the kind that you could easily see (then again the only plastic burn test result that's really relevant that I suspect is the only one that the supervisor at nats might mention at all if applicable to the test is PVC, which is green).
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Re: Forensics C

Postby markuswso17 » Thu May 25, 2017 4:40 pm

It's been a while since we took our nationals tests and it's been pretty quiet on the Forensics forum, so what was your favorite/least favorite part about Forensics this year?
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Re: Forensics C

Postby daydreamer0023 » Thu May 25, 2017 4:55 pm

It wasn't a bad test - my partner and I were just really bad at time management. However, the plastics solution containers were somehow contaminated with oil from the people before (we were in the 5th block) so we abandoned plastics. Apparently, the other team at our table said the hot water bath was filled up too high so they couldn't put their test tubes in proper - I'm not sure because I didn't do Benedict's test.
Last edited by daydreamer0023 on Sat May 27, 2017 10:37 pm, edited 1 time in total.
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Re: Forensics C

Postby markuswso17 » Thu May 25, 2017 4:59 pm

daydreamer0023 wrote:It wasn't a bad test - my partner and were just really bad at time management. However, the plastics solution containers were somehow contaminated with oil from the people before (we were in the 5th block) so we abandoned plastics. Apparently, the other team at our table said the hot water bath was filled up too high so they couldn't put their test tubes in proper - I'm not sure because I didn't do Benedict's test.

I had issues with the water bath as well. What I ended up doing was just balancing it with a test tube holder, but then when I came back, the solution had spilled inside because it came unbalanced somehow. We also didn't use a microscope because the microscope at our table (back-right) had a huge scratch on the lens so it was nearly impossible to figure out what we were looking at.
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Re: Forensics C

Postby alleycat03 » Fri May 26, 2017 2:59 am

This was my second test with the Woz, and I was definitely more prepared this time. I think the test was well written and very difficult, which is to be expected. My only complaint is that the microscope that my team had was really crappy. It was super difficult to focus and the lens was super dirty. It took too long to ID the hairs with the crappy microscope so I basically had to make educated guesses on about 1/2 of the hairs. Otherwise, the test was well-written, the Woz was strict but a good proctor, and I enjoyed taking the test.
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