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Re: Forensics C

Posted: February 3rd, 2015, 6:20 pm
by Nathan Ault
Okay, so . . . Does EVERYBODY else have the time and the materials to practice the qualitative analysis? I don't :( , so does anyone know if you can trust other peoples' reports on what the substances act like?

Also, for mass specs, WHAT IS WITH THEM? :? All the videos I've seen assume you know serious chemistry, which I don't. As soon as I start thinking I get it, it gets more confusing. Are we expected to find the structure of an unknown compound using nothing other than that bunch of vertical lines? How will knowing the formula help us in our analysis of the crime scene?

Re: Forensics C

Posted: February 3rd, 2015, 7:12 pm
by iwonder
Okay, so . . . Does EVERYBODY else have the time and the materials to practice the qualitative analysis? I don't :( , so does anyone know if you can trust other peoples' reports on what the substances act like?

Also, for mass specs, WHAT IS WITH THEM? :? All the videos I've seen assume you know serious chemistry, which I don't. As soon as I start thinking I get it, it gets more confusing. Are we expected to find the structure of an unknown compound using nothing other than that bunch of vertical lines? How will knowing the formula help us in our analysis of the crime scene?
Most highschool chem labs will have things needed for qual, really it's just the powders and some solutions, but yeah, I hate to say it but it's going to be a lot harder without at least looking at things like salt and sugar dissolving in water.

The problem is I might say that something dissolves in water, but if you dump 5x the amount of powder than I did (which you wouldn't know my methods) then it wouldn't look like it dissolves. If you're really careful then you could probably use other reports. Pictures would actually be best, imho.

For mass spec, all I've ever seen, when it's there, is matching some graphs. Technically you should be able to find the composition of the substance with it, and it doesn't take a _huge_ knowledge of chemistry, but don't freak out about it.

Re: Forensics C

Posted: February 4th, 2015, 5:42 pm
by Nathan Ault
Okay, so . . . Does EVERYBODY else have the time and the materials to practice the qualitative analysis? I don't :( , so does anyone know if you can trust other peoples' reports on what the substances act like?

Also, for mass specs, WHAT IS WITH THEM? :? All the videos I've seen assume you know serious chemistry, which I don't. As soon as I start thinking I get it, it gets more confusing. Are we expected to find the structure of an unknown compound using nothing other than that bunch of vertical lines? How will knowing the formula help us in our analysis of the crime scene?
Most highschool chem labs will have things needed for qual, really it's just the powders and some solutions, but yeah, I hate to say it but it's going to be a lot harder without at least looking at things like salt and sugar dissolving in water.

The problem is I might say that something dissolves in water, but if you dump 5x the amount of powder than I did (which you wouldn't know my methods) then it wouldn't look like it dissolves. If you're really careful then you could probably use other reports. Pictures would actually be best, imho.

For mass spec, all I've ever seen, when it's there, is matching some graphs. Technically you should be able to find the composition of the substance with it, and it doesn't take a _huge_ knowledge of chemistry, but don't freak out about it.
Thanks. I've heard that you shouldn't put too much of a substance in the water, so I'll make sure not to.

The example tests I've looked at don't seem to have tough mass spec, so I'm glad to hear this is the norm :) .

Re: Forensics C

Posted: February 5th, 2015, 3:22 pm
by samlan16
Thanks. I've heard that you shouldn't put too much of a substance in the water, so I'll make sure not to.

The example tests I've looked at don't seem to have tough mass spec, so I'm glad to hear this is the norm :) .
Yeah, at least where I compete, mass spec usually means matching. BUT there are sometimes tests where they ask real mass spec questions, so it wouldn't hurt to go over it.

Re: Forensics C

Posted: February 7th, 2015, 11:11 am
by Nathan Ault
Thanks. I've heard that you shouldn't put too much of a substance in the water, so I'll make sure not to.

The example tests I've looked at don't seem to have tough mass spec, so I'm glad to hear this is the norm :) .
Yeah, at least where I compete, mass spec usually means matching. BUT there are sometimes tests where they ask real mass spec questions, so it wouldn't hurt to go over it.
Yeah, I spent a couple hours (like, not just a couple) trying to wrap my mind around it. I got a couple of the concepts, but I couldn't tell anyone the structure or formula of a chemical just from looking at a mass spec.

Re: Forensics C

Posted: February 13th, 2015, 8:41 pm
by Leaf
Just got back from my first full experience of Forensics at competition... and I failed! I was not expecting a full on crime scenario to take up the entire event. I was moreso expecting half exam and half scenario, I guess I was wrong.

I was under pressure the entire time and having 10 bunsen burners on in the room didn't help with the sweating haha. Anyways, it's in the past now so oh well. I had a few issues with solubility. What should be the deciding factor for solubility? I feel like my powder analysis was completely thrown off by me thinking a powder is soluble when it's actually not and vice versa. I saw some solutions where the powder seemed kind of "suspended" in the liquid and others where i thought the powder was soluble but none of my further tests worked. What are your guys' go-to solutions for solubility?
Heh, time is probably the biggest challenge with this event... Just try a lot of practice tests and make sure you can get through the qual fast.

As far as solubility, I think the best advice is to try all the powders by yourself, come up with a really consistent method to test it, and then write down all your own results as you can describe them. It's a lot better than going off of internet descriptions.
For solubility, if it settles, it's doesn't dissolve. But to tell quick, if it makes a cloudy mixture, it's undissolvable. If the mixture is clear with some grains, or floating bits, it's dissolvable.
Try to go off of many sources to learn and get a generalized idea of what each powder will do, and definitely write it down. It won't be easy to memorize it all on the first try. If there are any people who did Forensics last year in your team, try to get in contact with them and get them to tell you all that they can tell you. That's how i learned, I went off of their info and tested all the powders side by side, comparing all of them lined up. Did multiple test on the same powder to find consistencies, inconsistencies, and distinct features. To get faster, what I did was get someone to set up 8 powders (or 10, or 12, the max per competitions) and time myself.(I sent 15mins for 8 at first) Memorized the distinctive features of the powders, I mostly rely on burn tests, almost all the powders burn differently. A few can be similar, but there's always something. If there isn't, then I just use process of elimination, and pH test to confirm it. Practice is the key to speed!(and memorization)

After doing so many practice test, I went from doing 8 powders in 50 mins(1st try, too long!!) getting 7/8, 8 in 20mins(2nd)6/8, then i forgot a lot, but with all the powders I got wrong I retested them. Now i can do 8 powders in 8 mins :} with 7/8 right, or around that time, 7-9 mins.

Re: Forensics C

Posted: February 21st, 2015, 10:54 am
by boomvroomshroom
Mass spec in general is kind of weird. Most of the questions asked were relatively simple, but sometimes they ask you to identify a compound based on mass spec alone...
Is there any way to do that quickly? I try using molar mass for the entire compound but even then it's a lot of guess/check and takes a while. Unless they're doing the mass spec for the powders listed in qualitative analysis, or something simple like water or the basic alcohols, I'm usually lost :(

Posted: March 2nd, 2015, 6:08 pm
by alwaysfaith
Has anyone does this event? What to expect/tips

Re:

Posted: March 2nd, 2015, 6:22 pm
by samlan16
Has anyone does this event? What to expect/tips
My best advice is to find all the compounds allowed in this event (your chem teacher should have most if not all of them) and scrutinize their reactions to water, HCl, Benedict's, NaOH, and KI as well as burn tests. Most of the physical evidence is simply matching, and hair, fibers, and plastics take little effort.

Re:

Posted: March 2nd, 2015, 8:58 pm
by boomvroomshroom
Has anyone does this event? What to expect/tips
Also learn to work with your partner. Unlike the study events you can't exactly carry this one.