Forensics C

[pikachu4919]

Hey guys, I have two questions. First, How do you continue your powders tests when you don't have any phenolphthalein to test with or alcohol for solubility? I ran into those problems in a test. Second, when referring to the angle of the blood splattering, how do you calculate that and which angle is it referring to (the angle between the opposite side and the hypotenuse or the angle between the adjacent side and the hypotenuse if you are using a right triangle to solve for it)?

First, why are phenolphthalein and alcohol absolutely necessary? The reagents provided will work as long as you know what identifies what. It helps to have a flowchart for the powders as well, making sure that all the steps are actually feasible using what's given and not very time-consuming at competition.

What do each reagents do, then?
EDIT: Ignore the edit.

OK. So the reagents are: 2M HCl, 2M NaOH, Benedict's solution, and Lugol's solution (or in short, iodine). Iodine can indicate Na2CO3 and cornstarch. HCl can indicate any of the carbonates. Benedict's is useful for NH4Cl and glucose. NaOH isn't really that useful although it can confirm NH4Cl.

Flame and pH tests are also very helpful, and so is conductivity although it's not as commonly used.

[thsom]

I created this one myself, but ...

unknown polymer
|
distilled water --floats--> 46% isopropyl alcohol --floats--> corn oil --floats--> PP
| | |
sinks sinks sinks
| | |
10% NaCl HDPE LDPE
| \
sinks floats --> PS
|
Saturated NaCl --floats--> 25% NaCl --floats--> PMMA
| |
sinks sinks
| |
flame PC
| \
green orange, shrivels w/ heat
| |
PVC PETE

EDIT: Oh shoot that did not turn out how I wanted it to ...

Could you possible post a picture asap? thanks!!!

[computergeek3]

Quick (hopefully) question:
At our regional competition last week, we were given two density solutions and told that we could use as much water as we wanted. How would you go about taking those solutions and changing their densities? I understand adding water would lower the density, but how would you know what the resulting density is without having a method by which to measure the amount of water?

[pikachu4919]

Could you possible post a picture asap? thanks!!!

I uploaded it to Flickr, but it doesn't show when I try to post the image ... this is the link to the image, though. Hope it helps!

http://www.flickr.com/photos/94067270@N ... /lightbox/

Quick (hopefully) question:
At our regional competition last week, we were given two density solutions and told that we could use as much water as we wanted. How would you go about taking those solutions and changing their densities? I understand adding water would lower the density, but how would you know what the resulting density is without having a method by which to measure the amount of water?

Wait what? ... what "density solutions" were you given? Water? Salt?

[kn_95]

Quick (hopefully) question:
At our regional competition last week, we were given two density solutions and told that we could use as much water as we wanted. How would you go about taking those solutions and changing their densities? I understand adding water would lower the density, but how would you know what the resulting density is without having a method by which to measure the amount of water?

I am guessing one of the solutions they give should have the heaviest density of all (even heavier than PETE)? In that case, I think you can just add more water in it and go backwards in the flow chart, meaning the one which sinks first will be PETE, sinks second will be PVC...

[kn_95]

By the way, how do we do TLC? And how do we do it at Nationals (in other words, what tools do they provide)?
Is there any difference between doing TLC on an aluminum sheet and doing TLC on a piece of a plastic plate?
Thanks!

[pikachu4919]

By the way, how do we do TLC? And how do we do it at Nationals (in other words, what tools do they provide)?
Is there any difference between doing TLC on an aluminum sheet and doing TLC on a piece of a plastic plate?
Thanks!

Although I haven't seen it before in my SciOly experience, I believe (more like I heard) that you set it up just like for paper chromatography but it's a glass slide with a silicon coating, probably google it for more information. I believe that it usually doesn't show up until nationals...so yeah. I can't really answer the second question because I've never seen TLC done with plastic or aluminum ...

[Kazen]

Is there a way to differentiate the type of glass from the refractive index? Could we be asked to measure and calculate the RI at the competition? c:

[pikachu4919]

Is there a way to differentiate the type of glass from the refractive index? Could we be asked to measure and calculate the RI at the competition? c:

Yes, there is. Use the same density solutions you are given for the plastics (the RI's of these liquids and the different types of glass the piece could be of should also be provided to you at competition). Drop the glass in each solution. When the glass appears to be invisible in one particular solution, then the glass has the same RI as the solution. Because the RI's of both the glass and the solution are provided, there is no need to measure or calculate it.

[piimasta314]

How do you know when to use a certain fingerprint test?
I know when not to use dusting, but for cyanoacrylate it can be used for lots of things...same with ninhydrin and iodine fuming. I looked up the special types of surfaces but those three can be used for nearly all surfaces.