Forensics C

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Re: Forensics C

Post by pikachu4919 » January 24th, 2013, 1:33 pm

computergeek3 wrote: One of the easiest ways to differentiate sodium chloride and sodium acetate is to dissolve both substances in water and smell them...sodium acetate generally smells like vinegar (it's actually used to flavor salt and vinegar chips) while sodium chloride smells like, well, nothing
I've never tried that ... but it does seem interesting. although I thought sodium acetate was basic and sodium chloride was acidic ...

also @computergeek3 ... that's a lot of events, and my four events are among yours! ... :O ... I wonder ...
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Re: Forensics C

Post by BoldlyGoingNowhere » January 24th, 2013, 1:50 pm

sciolyynerdd wrote:hi does anyone know how to identify the polymers that we are not allowed to burn?

also, im having trouble identifying between sodium chloride and sodium acetate.

thanks!
A lot of the time they'll give you burn test results (or photographs of the flames and what it looks like afterwards) for things like plastics.
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Re: Forensics C

Post by sciolyynerdd » January 24th, 2013, 5:00 pm

does anyone have a good chart for the plastics' densities?
thanks!
oh and their after burned pictures too!
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Re: Forensics C

Post by pikachu4919 » January 24th, 2013, 5:40 pm

I created this one myself, but ...

unknown polymer
|
distilled water --floats--> 46% isopropyl alcohol --floats--> corn oil --floats--> PP
| | |
sinks sinks sinks
| | |
10% NaCl HDPE LDPE
| \
sinks floats --> PS
|
Saturated NaCl --floats--> 25% NaCl --floats--> PMMA
| |
sinks sinks
| |
flame PC
| \
green orange, shrivels w/ heat
| |
PVC PETE

EDIT: Oh shoot that did not turn out how I wanted it to ...
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Nationals 2016 ~ 4th place Forensics


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Re: Forensics C

Post by EastStroudsburg13 » January 24th, 2013, 5:53 pm

I suggest you make your flowchart using Word, take a screenshot, upload it to tinypic, and then post it here. That should work better. :)
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Re: Forensics C

Post by pikachu4919 » January 24th, 2013, 5:58 pm

I don't have a tinypic ...
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Re: Forensics C

Post by EastStroudsburg13 » January 24th, 2013, 11:05 pm

That shouldn't matter, you should still be able to upload things. If you get an account, then you'll be able to keep track of things better, but if you don't really want to find it after you post it, then doing it without an account should be fine.
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Re: Forensics C

Post by thsom » January 26th, 2013, 7:39 pm

Hey guys, I have two questions. First, How do you continue your powders tests when you don't have any phenolphthalein to test with or alcohol for solubility? I ran into those problems in a test. Second, when referring to the angle of the blood splattering, how do you calculate that and which angle is it referring to (the angle between the opposite side and the hypotenuse or the angle between the adjacent side and the hypotenuse if you are using a right triangle to solve for it)?

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Re: Forensics C

Post by pikachu4919 » January 26th, 2013, 8:20 pm

thsom wrote:Hey guys, I have two questions. First, How do you continue your powders tests when you don't have any phenolphthalein to test with or alcohol for solubility? I ran into those problems in a test. Second, when referring to the angle of the blood splattering, how do you calculate that and which angle is it referring to (the angle between the opposite side and the hypotenuse or the angle between the adjacent side and the hypotenuse if you are using a right triangle to solve for it)?
First, why are phenolphthalein and alcohol absolutely necessary? The reagents provided will work as long as you know what identifies what. It helps to have a flowchart for the powders as well, making sure that all the steps are actually feasible using what's given and not very time-consuming at competition.

As for angle of impact on blood spattering, it is , where theta is the angle, W is the width, and L is the length. arcsin is also known as reverse sine. No complex computations required. Well, of course, arcsin is related to trig, but calculating trig by hand is not required. Seriously, don't try to make it hard on yourself.
Last edited by pikachu4919 on February 7th, 2013, 7:04 pm, edited 2 times in total.
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Nationals 2016 ~ 4th place Forensics


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Re: Forensics C

Post by sciolyynerdd » January 30th, 2013, 3:49 pm

Hii,

I don't understand what exactly do we have to learn for seeds and pollet & track and soil? Are we supposed to just match photographs?
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-Forensics 2012 6th place

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