Forensics C

Lumitailz
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Re: Forensics C

Postby Lumitailz » December 1st, 2016, 8:47 pm

Does Borax react the same way as Boric Acid? Especially flame-test and solubility-wise? My coach is reluctant to buy Boric Acid because we have Borax, but I want to make sure they are the same thing. I did some research and am wondering if the sodium in Borax would cause the flame to be yellow instead of green...

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pikachu4919
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Re: Forensics C

Postby pikachu4919 » December 1st, 2016, 9:57 pm

Does Borax react the same way as Boric Acid? Especially flame-test and solubility-wise? My coach is reluctant to buy Boric Acid because we have Borax, but I want to make sure they are the same thing. I did some research and am wondering if the sodium in Borax would cause the flame to be yellow instead of green...
Sodium turns everything yellow regardless of how much of it there is. But either way, despite that both borax and boric acid have boron in them, the boron is positioned in the molecules in totally different ways in that they have completely different chemical formulas (Na2B4O7·10H2O vs H3BO4, literally a buffer vs an acid), and thus, they will not react in the same ways. As much as we all wish it wasn't, chemistry is complicated, buddy.

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Re: Forensics C

Postby kathrynpereira » December 13th, 2016, 7:17 am

Just wondering, is salt the only powder with a cubic crystal? Silly question, I know. :P
I don't think crystal shape works well for IDing powders, although I haven't tried much. I think they're extremely variable, and lack of consistency makes it hard to ID. I would think that at least KCl would also have a cubic structure, since it's very similar chemically to NaCl.
Yeah I mean considering the national supervisor's description of sodium acetate is "very fine white powder" and the sample of sodium acetate we had at our school was medium-sized clear crystals, I'd say really don't rely on the physical appearance of the powder as a key identifier. There are plenty of other ones you can use that are far more robust.
Sodium acetate is a fine white powder but will become a crystal when exposed to water (ex. humidity) according to my cheat sheet

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Re: Forensics C

Postby bradyr18 » December 20th, 2016, 7:40 pm

Does anyone have the burn test results of PMMA, I know we can't conduct burn tests in the event but the rules specify that the results can be given.

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Re: Forensics C

Postby Panda Weasley » December 21st, 2016, 6:21 am

Does anyone have the burn test results of PMMA, I know we can't conduct burn tests in the event but the rules specify that the results can be given.
I believe that PMMA has a bright blue flame with no smoke and a fruity smell.

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Re: Forensics C

Postby pikachu4919 » December 27th, 2016, 5:29 pm

Does anyone have the burn test results of PMMA, I know we can't conduct burn tests in the event but the rules specify that the results can be given.
I believe that PMMA has a bright blue flame with no smoke and a fruity smell.
Idk about you guys but when I did this event, I felt like the only burn test result that I thought was absolutely necessary to know was PVC, which is a green flame, and then the rest can be determined by density.

Granted, this largely depends on the supervisors at each competition and what information they choose to provide for you, so don't take my word for it that PVC's flame is the only one you need to know.
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Re: Forensics C

Postby sciduck » December 27th, 2016, 8:32 pm

Does anyone have the burn test results of PMMA, I know we can't conduct burn tests in the event but the rules specify that the results can be given.
I believe that PMMA has a bright blue flame with no smoke and a fruity smell.
Idk about you guys but when I did this event, I felt like the only burn test result that I thought was absolutely necessary to know was PVC, which is a green flame, and then the rest can be determined by density.

Granted, this largely depends on the supervisors at each competition and what information they choose to provide for you, so don't take my word for it that PVC's flame is the only one you need to know.
I've seen questions on the burn test for PS and LDPE/HDPE too, but I would say that it definitely depends on test writers.
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Re: Forensics C

Postby Lumitailz » December 28th, 2016, 10:25 am

I never quite understood how to do density tests- Do you use a beaker and fill the whole thing up with liquid? Or can you use test tubes? Plastics have always been a part of the test I just guessed on.

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Re: Forensics C

Postby Magikarpmaster629 » December 28th, 2016, 11:17 am

I never quite understood how to do density tests- Do you use a beaker and fill the whole thing up with liquid? Or can you use test tubes? Plastics have always been a part of the test I just guessed on.
If you're doing plastics, the event supervisor will provide solutions of different densities. Since you can bring a chart with the densities of each plastic and the densities of the solutions, you can tell which plastics will sink/float in which solutions. At the event, you take the plastic and simply place it in the liquid to see whether it floats or sinks.
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Re: Forensics C

Postby Lumitailz » December 28th, 2016, 4:46 pm

I never quite understood how to do density tests- Do you use a beaker and fill the whole thing up with liquid? Or can you use test tubes? Plastics have always been a part of the test I just guessed on.
If you're doing plastics, the event supervisor will provide solutions of different densities. Since you can bring a chart with the densities of each plastic and the densities of the solutions, you can tell which plastics will sink/float in which solutions. At the event, you take the plastic and simply place it in the liquid to see whether it floats or sinks.
So for example, if the supervisors provide us with a large bottle of alcohol for a row to share, we can just dunk the plastic directly into the alcohol container?


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