Crime Busters B

[caseyotis]

Oh, awesome! You're really good, then. I don't have high expectations.

I just want to have fun with the event, but also know what I'm doing. I don't expect to medal.

Okay, thank you~ I'm going to brief through all of them (plastics, powders, polymers, etc.), then, if I have time, go deeper.

[Soccer_Girl]

I have a question. For blood splatters, do we have to identify if it was from a gun shot or a cut and that stuff? If so, how in the world are we supposed to do that??? Thanks so much!

[theriddler]

I just wanted to ask: how exactly do you test the plastics? That was one place we didn't do well at one of our invitationals.

Don't feel bad... You're not alone! First, let's discuss the theoretical intent... Supposedly, each polymer has a specific density, ranging from around .90 grams / cm3 to as much as 1.49 grams / cm3. The E/C should have at least 5 different liquids, each with different densities. These liquids, list from least dense to most dense are vegetable oil (.885 grams / cm3), 46% alcohol (.915 grams / cm3), fresh water (1.00 grams / cm3), 10% salt (1.10 grams / cm3), and 20% salt (1.16 grams / cm3). by placing a sample of the polymer in the various liquids and determining if it floats or sinks you should be able to determine the the specific density range between two liquids... In other words, if it sinks in 46% alcohol, but floats in water, you know that it must be between .915 and 1.0 density, right? That should really narrow down the possibilities. It's not fool proof... not all polymer samples, even of the same material, have the same density, they vary... also, they can have this very irritating tendency to have air bubbles adhere to them, really screwing the whole thing up, floating when they should be sinking. ALWAYS take your finger and poke them 3 or 4 times to see if you can get them to stay down.

Don't take anything as hard and fast rules... The density test should be used as a guideline only to steer you in the right direction, not as an elimination process.

If they give us liquids to use for identifying the plastics, they'll give us the densities of the liquids, right? And how would you tell the difference between high density polyethylene and low density polyethylene? The difference in density is only .025 g/cm. It says that the high density one is more translucent, but I couldn't find any pictures online of either of them.
Lastly, does sand give off a noticeable bad odor when iodine is added?

[computergeek3]

Lastly, does sand give off a noticeable bad odor when iodine is added?

It shouldn't...sand is a compound of silicon and oxygen (SiO2) so it should be extremely nonreactive. The only thing iodine is really good for is identifying cornstarch and Vitamin C.

[caseyotis]

Okay... It says on the wiki that ammonia has a "sweet" odor. However, in the kit that we got, it says that ammonia is NOT to be inhaled, and I accidentally did get a whiff of it and it smelled awful. My throat also did get a little bit irritated by it. Is this normal? At the competition, will we be able to open the beakers and sniff each liquid sample?

[geminicross]

I always assumed you were supposed to "wharf the smell" (spelling?)
You know, wave the scent towards you, so you're not inhaling it really.
But IDK.

[caseyotis]

I always assumed you were supposed to "wharf the smell" (spelling?)
You know, wave the scent towards you, so you're not inhaling it really.
But IDK.

Waft, I think. But okay, yeah, it was an accident and I wasn't being that careful, but... The Wiki describes it as smelling "sweet," and Ammonia was far from it. It smelled like something dead.

[geminicross]

Lol, thank you
(and yeah, when I printed out my cheat sheet, I remembered to replace Sweet with any other adjective)

[caseyotis]

Lol, thank you
(and yeah, when I printed out my cheat sheet, I remembered to replace Sweet with any other adjective)

I'm going to edit that out, I think. *shrug* What should I put instead? Nasty?

[aim4me26]

Lol, thank you
(and yeah, when I printed out my cheat sheet, I remembered to replace Sweet with any other adjective)

I'm going to edit that out, I think. *shrug* What should I put instead? Nasty?

I've also heard ammonia be described as pungent. That might work.