Forensics C

[salcedam]

Hey! I have an invitational this Saturday, and my partner and I were double checking the rules. We did not know anything about the cobalt blue glass under flame test equipment that teams are supposed to bring. We have some, but we do not know what it's used for. Can someone help me out with this?

Hey, are you going to Loyola?

And you hold up the cobalt blue glass next to the flame in order to absorb the yellow color of that the sodium ion gives off so as to see if it really is sodium or if sodium is just contaminating the sample you're burning.

[meggers1221]

so how do you tell nacl from sodium acetate?

[Phenylethylamine]

so how do you tell nacl from sodium acetate?

A solution of sodium acetate is basic (pH around 8), while a solution of sodium chloride is neutral.

[NinjaChicken]

I'm having trouble identifying plastics. Is it difficult to create your own ~40% iso. alcohol or 10% NaCl and I'm just not getting the right solutions? I've had PETE float in my 10% NaCl water solution. Or is there a certain way to test it that makes the difference? Do you drop the plastic in, or do you bring it right to the surface and 'dip' it into the solution?

[salcedam]

I'm having trouble identifying plastics. Is it difficult to create your own ~40% iso. alcohol or 10% NaCl and I'm just not getting the right solutions? I've had PETE float in my 10% NaCl water solution. Or is there a certain way to test it that makes the difference? Do you drop the plastic in, or do you bring it right to the surface and 'dip' it into the solution?

Drop the PETE into the 10% NaCl solution with a little more force than just merely dropping it in because sometimes a plastic may float because of the surface tension so to break the surface tension of the liquid, don't chuck it in the solution, but put a little weight into dropping the plastic and then see if it sinks or floats.

[jkting3]

At the Tiger invitational, there was a plastic sample that was relatively clear that we had to identify. The solutions we were provided were of density 0.92, 0.94, 0.96, and 1.10. I had a hunch that based on the clarity of the sample, it would be either PC/PMMA, so I just tested in the 1.10 solution. The sample sank, which means it could be PC, PMMA, Nylon 6-6, PETE, or PVC. No burn test results were provided. I ended up guessing PC, but the correct answer was PETE. I know it could be difficult to help me with this description, but I was wondering in this kind of situation, how would I be able to correctly identify the polymer?

[personasaurus rex]

At the Tiger invitational, there was a plastic sample that was relatively clear that we had to identify. The solutions we were provided were of density 0.92, 0.94, 0.96, and 1.10. I had a hunch that based on the clarity of the sample, it would be either PC/PMMA, so I just tested in the 1.10 solution. The sample sank, which means it could be PC, PMMA, Nylon 6-6, PETE, or PVC. No burn test results were provided. I ended up guessing PC, but the correct answer was PETE. I know it could be difficult to help me with this description, but I was wondering in this kind of situation, how would I be able to correctly identify the polymer?

In your defense, those were poorly selected solutions. Normally the solutions I've seen at well-written tests were water, 25%NaCl, Sat. NaCl, 46% Isopropyl, and vegetable oil. those would only get you pairs of plastics that you cannot further identify, at which time you would see if they gave you burn test results, which most times they do. however, your test could have just been poorly written.

[AzureWotan]

So depending on the writers of the tests they can set us up for failure.
Great
I know its not their fault, but still.

[AzureWotan]

Also, Im here.
Any suggestions on the notes? So far theres nobody else from my school or even state who posts on the forums so I cant ask them for help.
Sorry to bother you >.>

[AlphaTauri]

So depending on the writers of the tests they can set us up for failure.
Great
I know its not their fault, but still.

Define "failure" - sure you may not be able to answer some of the questions correctly, but if the test is that badly written (or the key is wrong), neither will anyone else. In the end, you don't have to get an A to win, you just have to do better than everyone else. Although I agree, bad tests are very, very frustrating.

Also, Im here.
Any suggestions on the notes? So far theres nobody else from my school or even state who posts on the forums so I cant ask them for help.
Sorry to bother you >.>

I'd definitely put a flowchart on there for powders and plastics, as well as what each powder/plastic is used for (unless you're sure you can remember all that stuff while under pressure). Past that, it's just whatever you think you need help remembering...I had a little bit of info on nearly every section.

It really depends on what your strengths and weaknesses are. I completely left out mass spectrometry because I didn't understand it anyways, and I thought that the space it would take to explain it to myself would be better used reminding myself of things (fingerprinting details, fibers, etc.) that I would more likely get correct.