Forensics C

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courage7856
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Re: Forensics C

Post by courage7856 »

Phenylethylamine wrote:
courage7856 wrote:We each got 5 of 6, with the same one (cornstarch) tripping us up.
Correct me if I'm wrong, but I think cornstarch is the only powder on the list this year that changes color with KI solution... Did you not have iodine?
We did, but some of the other things didn't seem so cornstarchy. . .mine seemed purple when I burned it (I'd just cleaned my wire so it wasn't contaminated, and I haven't seem potassium chloride in a while, so I'm not sure why), so I thought it was KCl. My partner, for some reason, thought it was Ca(NO3)2, also because of flame test. I asked him to show me, but then, of course, it looked nothing like that.
Last edited by courage7856 on March 11th, 2011, 4:01 pm, edited 1 time in total.
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Re: Forensics C

Post by personasaurus rex »

courage7856 wrote:
Phenylethylamine wrote:
courage7856 wrote:We each got 5 of 6, with the same one (cornstarch) tripping us up.
Correct me if I'm wrong, but I think cornstarch is the only powder on the list this year that changes color with KI solution... Did you not have iodine?
We did, but some of the other things didn't seem so cornstarchy. . .mine seemed purple when I burned it (I'd just cleaned my wire so it wasn't contaminated, and I haven't seem potassium chloride in a while, so I'm not sure why), so I thought it was KCl. My partner, for some reason, thought it was CaNO3, also because of flame test. I asked him to show me, but then, of course, it looked nothing like that.
It can't possibly be KCl or Ca(NO3)2 because they're both soluble in water. Cornstarch is clearly insoluble, and that should keep you on the right track
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Re: Forensics C

Post by ribonucleicacid621 »

Sometimes you can have problems doing iodine test with cornstarch. Make sure the concentration of cornstarch in the test tube is high enough, otherwise it may not change color. This happened to my partner during invitationals.
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Re: Forensics C

Post by nanowhale »

For the chemical test really you only need about two or three tests to narrow it down for example, flame tests, pH and one other is about enough. However, you have to be well rounded on everything, something I learned the hard way this year. Chromatography has been tested every year since I have been doing it (even during Sci. Crime Busters div. B) but, don't focus too much on the powders/ compounds find a good balance between all of the topics listed.
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Re: Forensics C

Post by Phenylethylamine »

ribonucleicacid621 wrote:Sometimes you can have problems doing iodine test with cornstarch. Make sure the concentration of cornstarch in the test tube is high enough, otherwise it may not change color. This happened to my partner during invitationals.
If you drip Lugol's solution (KI) onto cornstarch- straight onto the powder, in a well plate or something like that, not in solution- you should definitely see it change color.
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Re: Forensics C

Post by personasaurus rex »

Phenylethylamine wrote:
ribonucleicacid621 wrote:Sometimes you can have problems doing iodine test with cornstarch. Make sure the concentration of cornstarch in the test tube is high enough, otherwise it may not change color. This happened to my partner during invitationals.
If you drip Lugol's solution (KI) onto cornstarch- straight onto the powder, in a well plate or something like that, not in solution- you should definitely see it change color.
PHENYL! Congrats to you and your team. =]
I don't know if you did powders or not, but do you remember what powders there were? I'm just really curious if I actually got them right or was just falsely confident.
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Re: Forensics C

Post by Phenylethylamine »

personasaurus rex wrote:
Phenylethylamine wrote:
ribonucleicacid621 wrote:Sometimes you can have problems doing iodine test with cornstarch. Make sure the concentration of cornstarch in the test tube is high enough, otherwise it may not change color. This happened to my partner during invitationals.
If you drip Lugol's solution (KI) onto cornstarch- straight onto the powder, in a well plate or something like that, not in solution- you should definitely see it change color.
PHENYL! Congrats to you and your team. =]
I don't know if you did powders or not, but do you remember what powders there were? I'm just really curious if I actually got them right or was just falsely confident.
Thanks! I did powders, but not especially well (I've done Forensics at only one competition prior to States, and the fact that I used to do Science Crime Busters is pretty unhelpful since nearly all the powders/reagents are different). All I know for sure (at least, fairly sure) is that there was a glucose (Benedict's turned red), a potassium chloride (violet flame test) and probably at least one sodium chloride (crystalline + yellow flame test- less conclusive than the other two, though). I mostly guessed on the others.
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Re: Forensics C

Post by personasaurus rex »

oh haha well you did well anyways so doesn't even matter =P
I was just reaaaly curious because one of the questions was like "which given powder is used for Silly Putty" and its H3BO3 but i didn't get H3BO3 in the powders... I even checked them all over three times! It's been gnawing at me lol
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Re: Forensics C

Post by Phenylethylamine »

personasaurus rex wrote:I was just reaaaly curious because one of the questions was like "which given powder is used for Silly Putty" and its H3BO3 but i didn't get H3BO3 in the powders... I even checked them all over three times! It's been gnawing at me lol
I wrote boric acid for one of them (the first one, if I recall correctly), although it was more or less a guess. Got the question wrong, though; I had a bunch of uses for the powders on my notes sheet, but Silly Putty wasn't one of them.
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Re: Forensics C

Post by Sae »

Just curious. Does anyone else's regionals give hardly enough time to do the event? We only identified 4/8 powders and no fibers or polymers. I went through and did as much as I could in the last 15 minutes to figure it out.
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