Forensics C

C8H10N4O2!
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Re: Forensics C

Postby C8H10N4O2! » February 19th, 2019, 7:40 pm

olhs4n6 wrote:
JJC28 wrote:How much can you rely on the appearance of the powder for the purpose of identifying it?


I usually only use the appearance as a last resort to narrowing down. Lets say there are 2 with a yellow flame test, and they have the same solubility, etc. then I would go to the appearance...

I think they were referring to tests where there are no flame tests...
Some of the powders I have worked with are a little more rectangular in their shape. I don't know exactly how to describe it, would highly recommend looking them up, but also, some of the powders are slightly hygroscopic and would clump together. Also, keep in mind that if the event does jot have the gas or bunsen burners for flame tests, it is unlikely that they will considered grinding down the powders beyond their original form.
Between this and pH I think you can narrow it down and then go with gut instinct/what is on the suspect info sheets.

scienceisfunalil
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Re: Forensics C

Postby scienceisfunalil » February 20th, 2019, 7:12 am

C8H10N4O2! wrote:
olhs4n6 wrote:
JJC28 wrote:How much can you rely on the appearance of the powder for the purpose of identifying it?


I usually only use the appearance as a last resort to narrowing down. Lets say there are 2 with a yellow flame test, and they have the same solubility, etc. then I would go to the appearance...

I think they were referring to tests where there are no flame tests...
Some of the powders I have worked with are a little more rectangular in their shape. I don't know exactly how to describe it, would highly recommend looking them up, but also, some of the powders are slightly hygroscopic and would clump together. Also, keep in mind that if the event does jot have the gas or bunsen burners for flame tests, it is unlikely that they will considered grinding down the powders beyond their original form.
Between this and pH I think you can narrow it down and then go with gut instinct/what is on the suspect info sheets.


Hi folks, I have two questions!

One is should we express Rf values in decimals or fractions?
Second is do regionals/states typically follow the chart of how many powders, polymers, etc to give at different levels? Or will they sometimes give more? I’m from FL if that helps.
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Re: Forensics C

Postby c21k » February 20th, 2019, 7:17 pm

scienceisfunalil wrote:
C8H10N4O2! wrote:
olhs4n6 wrote:
I usually only use the appearance as a last resort to narrowing down. Lets say there are 2 with a yellow flame test, and they have the same solubility, etc. then I would go to the appearance...

I think they were referring to tests where there are no flame tests...
Some of the powders I have worked with are a little more rectangular in their shape. I don't know exactly how to describe it, would highly recommend looking them up, but also, some of the powders are slightly hygroscopic and would clump together. Also, keep in mind that if the event does jot have the gas or bunsen burners for flame tests, it is unlikely that they will considered grinding down the powders beyond their original form.
Between this and pH I think you can narrow it down and then go with gut instinct/what is on the suspect info sheets.


Hi folks, I have two questions!

One is should we express Rf values in decimals or fractions?
Second is do regionals/states typically follow the chart of how many powders, polymers, etc to give at different levels? Or will they sometimes give more? I’m from FL if that helps.


1) I always express my Rf values in decimals. That's the way I was taught and seem to be getting points for it thus, I haven't checked if fractions are acceptable. Regardless of fraction or decimal, make sure you show your work when calculating Rf. I lost points at the Solon invite for not doing so.

2) I have found that regionals and states will always abide by the rules manual charts at least in Ohio. Florida SHOULD abide by the rules as well.
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Re: Forensics C

Postby SpicyCurry » February 25th, 2019, 9:52 am

So for the different density liquids to test plastics. Do they give us the density of the liquids they're providing, or is there a list out there that we need to know?

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Re: Forensics C

Postby Crimesolver » February 25th, 2019, 10:01 am

SpicyCurry wrote:So for the different density liquids to test plastics. Do they give us the density of the liquids they're providing, or is there a list out there that we need to know?

https://www.google.com/search?biw=1313& ... _WEO4VC9iM:
Sometimes they give you other substances like hydrogen peroxide or different alcohol concentrations, but this is the most common.

edit: oh yeah you should probably search up the densities for each of these substances
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Re: Forensics C

Postby Lilliankg16NHHS » March 11th, 2019, 4:58 pm

Hey everyone, I've got state this weekend and I was wondering if anyone had some tips for forensics. I've only done it once at an invitational and forgot to learn about qualitative analysis so that brought my score down quite a bit.

On another note, if anyone has a well-organized notes sheet, let me know mines a little messy :P

Thanks :)
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Re: Forensics C

Postby olhs4n6 » March 11th, 2019, 5:40 pm

Lilliankg16NHHS wrote:Hey everyone, I've got state this weekend and I was wondering if anyone had some tips for forensics. I've only done it once at an invitational and forgot to learn about qualitative analysis so that brought my score down quite a bit.

On another note, if anyone has a well-organized notes sheet, let me know mines a little messy :P

Thanks :)



Page 4 has some really good tips from pikachu, they helped me get 1st at my regionals. Best of luck at states!

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Re: Forensics C

Postby wec01 » March 11th, 2019, 7:13 pm

Lilliankg16NHHS wrote:Hey everyone, I've got state this weekend and I was wondering if anyone had some tips for forensics. I've only done it once at an invitational and forgot to learn about qualitative analysis so that brought my score down quite a bit.

On another note, if anyone has a well-organized notes sheet, let me know mines a little messy :P

Thanks :)


In general just plan beforehand how you're going to tackle everything. The test is somewhat predictable in format but it tends to be fast paced so an important way to prepare is just knowing what you will have to do and planning beforehand how you'll spend your time. At competition, try to stick to your plan, but if you start running low on time or something takes longer than expected, try to prioritize points. Some parts will be worth more than others so if you don't think you will finish, try to quickly gauge what you think will get you quick points and focus on those (one big priority is to have something down for a conclusion as it is worth a large portion of the test).

As for the cheat sheet, it's fine if it's a bit messy or disorganized, what's more important is that you know where everything is and can quickly find things.
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Re: Forensics C

Postby dnzsnr » March 11th, 2019, 8:42 pm

Anyone have a link to a good dichotomous key to use for powders?

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Re: Forensics C

Postby olhs4n6 » March 12th, 2019, 9:18 am

dnzsnr wrote:Anyone have a link to a good dichotomous key to use for powders?


I think the Princeton test had a good list of uses, but not for all the powders. Let me know if you find something better though.

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Re: Forensics C

Postby jimmy-bond » March 13th, 2019, 9:15 am

dnzsnr wrote:Anyone have a link to a good dichotomous key to use for powders?

I use a chart, not sure if there are any physical dichotomous keys but the intellectual bois probably have the sequence of testing memorized. I suggest that you start with a flame test and go from there.
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Re: Forensics C

Postby wec01 » March 13th, 2019, 3:28 pm

jimmy-bond wrote:
dnzsnr wrote:Anyone have a link to a good dichotomous key to use for powders?

I use a chart, not sure if there are any physical dichotomous keys but the intellectual bois probably have the sequence of testing memorized. I suggest that you start with a flame test and go from there.


Yeah the flame test is very helpful and can single out a large number of the powders. It also can help to consider what each of the powders look like and quickly narrow it down before doing some tests.
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Re: Forensics C

Postby dnzsnr » March 15th, 2019, 4:47 am

Do polar or non polar substances travel farther in chromatography (using water as solvent)?

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Re: Forensics C

Postby wec01 » March 15th, 2019, 5:52 am

dnzsnr wrote:Do polar or non polar substances travel farther in chromatography (using water as solvent)?


I believe polar substances would travel further because they would attract to the water molecules

Edit: I'm actually not sure about this since I believe in paper chromatography the paper is polar as well
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Re: Forensics C

Postby wec01 » March 17th, 2019, 2:36 pm

What are some common mass spectra that come up on tests? I've noticed hexane and caffeine are both relatively common, and I was wondering if there were others.
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