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Re: Forensics C

Posted: January 4th, 2015, 4:57 pm
by iwonder
One thing that I always found helpful for with flame tests is to use new nichrome every time. I know it sounds wasteful, and if you're really careful about cleaning it shouldn't matter, but I had a spool of nichrome wire that I would cut and bend (takes a few seconds) and take those to the contest in a clean paper towel or something disposable. All I had to do was stick one end in a cork and dip the other end in the solution that I had (since I did water solubility before flame tests) and some of the powder if I needed the extra color, and burn it. Then it just goes in the trash. After the initial second or two that nichrome burns the first time, I never had sodium contamination in a flame test (unless I was stupid and forgot to scrub that one spot on the plate or something).

Mass Spec

Posted: January 29th, 2015, 4:29 pm
by _vanemchir_
hey guys I'm kinda lost in mass spec. Can anyone explain to me how to analyze a mass spec graph I've looked at several videos on youtube but none seem to be helping :(
Thanks, Vane

Re: Mass Spec

Posted: January 29th, 2015, 6:08 pm
by Skink
hey guys I'm kinda lost in mass spec. Can anyone explain to me how to analyze a mass spec graph I've looked at several videos on youtube but none seem to be helping :(
Thanks, Vane
I don't have time to prepare a homemade explanation right now myself, but a thought I had was that, in effort to search for mass spec 'in English' that you do a Google search for 'ib mass spectrometer' or equivalent because IB chemistry includes mass spec in the curriculum, whereas AP (far more common in this country as far as I'm aware) does not. I found a couple promising (I mean, compared to some of what is out there) deals on Slideshare as a result of this.

Edit: You could also run a board search here.

Re: Forensics C

Posted: February 3rd, 2015, 11:48 am
by Bozongle
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?

Re: Forensics C

Posted: February 3rd, 2015, 11:52 am
by iwonder
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.

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.