Forensics C

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Re: Forensics C

Post by JT016 » March 2nd, 2016, 7:30 pm

This test is located in the test exchange: http://www.scioly.org/wiki/images/3/3a/ ... Test_3.pdf

I was wondering if anyone had the answer key to this test? If so, that'd be great!

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Re: Forensics C

Post by JT016 » March 3rd, 2016, 7:11 pm

Another question:
What's a good way to differentiate PETE, PVC, PC, and PMMA? All of their densities are greater than that of a saturated NaCl solution(PMMA and PC are approximately equal). My teacher mentioned that stepping on a sample of PC and PMMA would be a good way to differentiate those, because of how they react to force. I believe PC will crack whereas PMMA will shatter into smaller pieces (though I am not 100% sure). How would I differentiate PETE and PVC? Would I have to rely on burn test results?

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Re: Forensics C

Post by pikachu4919 » March 20th, 2016, 10:20 pm

JT016 wrote:Another question:
What's a good way to differentiate PETE, PVC, PC, and PMMA? All of their densities are greater than that of a saturated NaCl solution(PMMA and PC are approximately equal). My teacher mentioned that stepping on a sample of PC and PMMA would be a good way to differentiate those, because of how they react to force. I believe PC will crack whereas PMMA will shatter into smaller pieces (though I am not 100% sure). How would I differentiate PETE and PVC? Would I have to rely on burn test results?
Usually I distinguish PC and PMMA from 25% NaCl (which has a density of ~1.19 g/cm^3, provided that it's made correctly, so PC will sink and PMMA will float). I've never heard of stepping on it to differentiate them, but it sounds like an interesting thing to do :lol: For PETE and PVC, you are correct in that you have to rely on burn test results, and supervisors will provide those if they're necessary to tell the difference.
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Re: Forensics C

Post by Magikarpmaster629 » March 23rd, 2016, 12:57 pm

So does the ES give salt in a solution or as crystals for plastic density tests?
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Re: Forensics C

Post by Panda Weasley » March 23rd, 2016, 1:28 pm

Magikarpmaster629 wrote:So does the ES give salt in a solution or as crystals for plastic density tests?
Usually the ES has all of the solutions already set up (meaning you can't make your own). I have never seen or heard of a time when competitors had to make the solutions.
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Re: Forensics C

Post by Magikarpmaster629 » March 23rd, 2016, 2:38 pm

Panda Weasley wrote:
Magikarpmaster629 wrote:So does the ES give salt in a solution or as crystals for plastic density tests?
Usually the ES has all of the solutions already set up (meaning you can't make your own). I have never seen or heard of a time when competitors had to make the solutions.
Okay. Do they tell you the concentrations of the solutions or do you have to guess based on the plastics?
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Re: Forensics C

Post by samlan16 » March 23rd, 2016, 6:27 pm

Magikarpmaster629 wrote:
Panda Weasley wrote:
Magikarpmaster629 wrote:So does the ES give salt in a solution or as crystals for plastic density tests?
Usually the ES has all of the solutions already set up (meaning you can't make your own). I have never seen or heard of a time when competitors had to make the solutions.
Okay. Do they tell you the concentrations of the solutions or do you have to guess based on the plastics?
When they have density testing set up, yes.

But keep in mind that not every ES will provide materials for density testing, so you will need to rely on any information given about burn test results.
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Re: Forensics C

Post by Magikarpmaster629 » March 27th, 2016, 8:43 am

What am I looking for in NaOH tests? There doesn't seem to be much going on...
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Re: Forensics C

Post by samlan16 » March 27th, 2016, 1:13 pm

Magikarpmaster629 wrote:What am I looking for in NaOH tests? There doesn't seem to be much going on...
Try reacting MgSO4 with NaOH- a precipitate of Na2SO4 should result.
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Re: Forensics C

Post by pikachu4919 » March 30th, 2016, 7:24 pm

samlan16 wrote:
Magikarpmaster629 wrote:What am I looking for in NaOH tests? There doesn't seem to be much going on...
Try reacting MgSO4 with NaOH- a precipitate of Na2SO4 should result.
You mean a Mg(OH)2 precip, right? Oh, adding onto that, Ca(NO)3 can also precip to form Ca(OH)2, which is also known as lime (not the fruit - if you've ever heard of limewater, that's a component of it), but the Mg(OH)2 is generally a lot more gel-looking and solid than the Ca(OH)2, which is more powdery although it still forms a settling solid. This is because Mg(OH)2 is completely insoluble while Ca(OH)2 is marginally soluble.
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