Forensics C

[BoldlyGoingNowhere]

How do you tell the difference between PVC/PETE and PMMA/PC? I know that between PVC and PETE, they both sink with saturated NaCl so is the only distinguishing factor by their transparencies? Also between PMMA and PC, they're both transparent and float in NaCl, so is there some other distinguishing factor if they do not provide burn test results/uses?

If they don't provide burn test results, I'm in trouble too. PVC burns with a green flame, PETE and PC burn with orange flames, and PMMA burns with a blue flame. Sorry if this doesn't help.

[BoldlyGoingNowhere]

Anyone looking for mass spectra, the best I can tell you is that different components of whatever it is will have differently sized spikes on the graph. These spikes are unique to different components.
Random info that may/may not help: for molecules over 1000 daltons, the standard by which everything else is measured is a horse-heart myoglobin. For molecules under 1000 daltons, it's Glu-1 fibrinopeptide B. m/z is mass to charge.

[willowmist]

Alpha, yes, I was at Conestoga today. What did you think of the test? Both our A and B teams did pretty badly (I got 12th, bleh); we kind of failed polymers and I mixed up three of the powders... and we ran out of time for the analysis and ended up writing it with wrong information. Ouch.

Mass spectra: As I understand (I don't), the graph shows the different components as they are read. I think due to different rates of moving or something, the components are read at different times, causing the spacing on the graph. Sometimes a molecule is split up into different molecules or atoms (H2O can be first read as H, then H2, then H2O, I think?) and these will be very close together. As such, usually the very last peak represents the molar mass or whatever it was of the entire substance; if there are isotopes, then it is the average of the two...? The base peak is the tallest peak. I found this really helpful: http://ull.chemistry.uakron.edu/gcms/2-MS%20interp.pdf Look around the internet yourself, because I'm probably wrong, so don't listen to me. >___<

[AlphaTauri]

Ah yeah, I was really surprised by my medal in 4n6 today. I thought it was a good test overall though, and with a very amusing story.

My partner and I were pretty uncertain on powders/plastics, even though I think we got them right - we need more time in the lab, methinks. Fingerprints and bloodstains were pretty easy; fibers was sorta sketchy, but we got it in the end I think; we wrote down random stuff for mass spec (lol, we had no clue what to do); and I think we screwed up chromatography because none of the Rfs matched...

I got about halfway through the written analysis, but I got enough to definitely implicate one suspect (Hermione) and possibly another (Harry), and said to let the other two go.

[willowmist]

Congrats! Also, 4n6... I get it. Ahah, that's clever. Or I'm just slow.

What were your answers for the powders? I was pretty confident about my answers, but it turned out that I only got NaHCO3 and ammonium chloride correct... I thought that the first powder was cornstarch, since didn't it turn black with iodine? Bleh, strange. My partner says she used the densities and density solutions for plastics, but we ended up getting all of them wrong. xP We knew mass spec, but when we wrote the answers down for the first two, we switched them. I don't know how to find the formula of the compound from the graph, though. And for the Rfs, how would you know the exact distance the water travels up to? Is the ratio always the same for each kind of ink? For us, the water stopped at the top, at the pencil/tape. Couldn't it have kept on going, and so then the values would have been different? And we ended up losing a lot of points for the analysis because we messed up powders and plastics...

[AlphaTauri]

Haha, 4n6 isn't my abbreviation. I stole it from hftf (who doesn't hang around here much anymore).

I believe I said the first one was sodium acetate (I thought it was cornstarch too, but it didn't change colour with I2). I also got ammonium chloride - turned blue/purple with Benedict's, right? I think we said regular old salt for 2, then sucrose for one of them, and I can't remember the last one...NaHCO3 perhaps?

My partner did plastics, so I dunno about that.

And yeah, the chromatography was weird...we marked the start and end points for the water, but I guess we let it go too long or something, because we got Rfs that were way too small to match any of the suspects.

Did you get a result of somewhere around 4ft for the origin height of bloodstain A? I'd never done that before, so I BS'd it with SOHCAHTOA. Also, what kind of hair and fiber did you say the samples were? We said cat hair and silk, but we weren't very sure.

[willowmist]

That's such a clever abbreviation, lol.

Yes, I remember ammonium chloride was the last one, and NaHCO3 was the third one. Did you get your test back? For salt and sucrose, I think I thought that the flame tests didn't ignite, and mixed it up with magnesium sulfate. If it doesn't ignite, does that just mean the flame doesn't change...?

How would you know when to stop the chromatography? Wouldn't the water just keep on going, and that would change the Rf a lot? Our Rfs were actually right, sort of... 0.326, 0.804, 0.866, and 0.976. (there were four dyes, right? Or was it three?)

I didn't know how to do the point of origin for the bloodstains. We were running out of time, so I just skipped it. >___< What did you get for the angles of impact? I used sin(angle) = (w/l) and got angles of 40 and 22, but they were marked wrong.

I didn't do fibers, but my partner put cat hair and linen. Cat hair was correct, while linen wasn't. I think she said that she was debating between linen and nylon, and nylon also matches Hermione (I think), so it could have been nylon.

[AlphaTauri]

The sugar I remember smoked pretty obviously when I took it out of the flame; salt turned the blue burner flame to orange (anything with sodium will turn it orange, actually).

I think our chromatography was just messed up...they didn't give us a beaker right away, so we resorted to a test tube, which may have screwed up our answers. I saw two main inks, a pink-ish one and one that was sort of olive-coloured?

The angles I remember I got were 38 and somewhere around 20 (haven't gotten our tests from our coach yet, so I dunno if any of my answers are right). You might have rounded the measurements or something? I was really OCD about it. Point of origin the way I did it was since I know the impact angle and the distance from the bloodstain to the convergence point, I did tan(38) = (height of origin point)/(distance from convergence point) and rearranged it to solve for the height.

Ah, cat hair was right? Good. I remember that silk matched Hermione, because my partner was relatively sure it was wool, which matched none of the suspects - silk burns in a similar way.

[personasaurus rex]

Anyone who went to Athens yesterday know what the two plastics were? I was pretty certain about my answers but they turned out to be wrong and we didn't receive answer keys at the end of the competition...

[quizbowl]

Anyone who went to Athens yesterday know what the two plastics were? I was pretty certain about my answers but they turned out to be wrong and we didn't receive answer keys at the end of the competition...

I think the answer keys were digital for Forensics, check the USB?