Forensics C

Lumitailz
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Re: Forensics C

Postby Lumitailz » Fri Dec 02, 2016 4:47 am

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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Re: Forensics C

Postby pikachu4919 » Fri Dec 02, 2016 5:57 am

Lumitailz wrote: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 » Tue Dec 13, 2016 3:17 pm

pikachu4919 wrote:
Magikarpmaster629 wrote:
daydreamer0023 wrote: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 » Wed Dec 21, 2016 3:40 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.

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Re: Forensics C

Postby Panda Weasley » Wed Dec 21, 2016 2:21 pm

bradyr18 wrote: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 » Wed Dec 28, 2016 1:29 am

Panda Weasley wrote:
bradyr18 wrote: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 » Wed Dec 28, 2016 4:32 am

pikachu4919 wrote:
Panda Weasley wrote:
bradyr18 wrote: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 » Wed Dec 28, 2016 6:25 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.

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Re: Forensics C

Postby Magikarpmaster629 » Wed Dec 28, 2016 7:17 pm

Lumitailz wrote: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 » Thu Dec 29, 2016 12:46 am

Magikarpmaster629 wrote:
Lumitailz wrote: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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Re: Forensics C

Postby Panda Weasley » Thu Dec 29, 2016 4:57 pm

Lumitailz wrote:
Magikarpmaster629 wrote:
Lumitailz wrote: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?

The solutions are typically in large beakers that you share with everyone (from my experience). Make sure you remember to take your plastics out. Don't be that person!
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Re: Forensics C

Postby bradyr18 » Wed Jan 04, 2017 12:47 am

Has anyone found a reliable conductivity tester? We've tried both homemade testers and flinn science testers and neither has consistently worked for us? Thanks

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Re: Forensics C

Postby pikachu4919 » Wed Jan 04, 2017 7:07 pm

bradyr18 wrote:Has anyone found a reliable conductivity tester? We've tried both homemade testers and flinn science testers and neither has consistently worked for us? Thanks


Is your issue that the tester always lights up with a dissolved solution of any powder?
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Re: Forensics C

Postby bradyr18 » Wed Jan 04, 2017 7:25 pm

pikachu4919 wrote:
bradyr18 wrote:Has anyone found a reliable conductivity tester? We've tried both homemade testers and flinn science testers and neither has consistently worked for us? Thanks


Is your issue that the tester always lights up with a dissolved solution of any powder?


One of the testers (our homemade one) always lit up on solution, the other (Flinn) never lit up which may have been from a bad lightbulb

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Re: Forensics C

Postby pikachu4919 » Wed Jan 04, 2017 8:54 pm

bradyr18 wrote:
pikachu4919 wrote:
bradyr18 wrote:Has anyone found a reliable conductivity tester? We've tried both homemade testers and flinn science testers and neither has consistently worked for us? Thanks


Is your issue that the tester always lights up with a dissolved solution of any powder?


One of the testers (our homemade one) always lit up on solution, the other (Flinn) never lit up which may have been from a bad lightbulb


I remember a couple years ago we ran into the same problem with our testers always lighting up, and we figured out the reason why the homemade one always lights up is because of strong vs weak electrolytes. Some of the powders will completely dissolve in water, and the presence of so many dissociated particles allow the solution to very effectively conduct electricity, which will cause the bulbs on the tester to shine very brightly. But there are other powders that are weak electrolytes, which will dissolve in water, but not completely dissociate like strong electrolytes. Those ones will still be able to conduct electricity, but not as well, so the bulbs will still shine, but the light given off will be significantly weaker. A good way to test this is to look at NaCl (a strong electrolyte) vs. sucrose (a weak one).

There are three possibilities for the Flinn one: 1. It's not on (it has an on/off switch), 2. the 9V battery is dead, 3. as you said, the lightbulb is dead. Check those before buying a new one.
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