Forensics C

[pb+ellie]

My worst area is human hair ids, so does anyone have a really great study tool I could use?

[Dragonshark]

My worst area is human hair ids, so does anyone have a really great study tool I could use?

I've mainly focused on distinguishing hair between different species, not between different people, but maybe this page can help, if you haven't already looked at it: http://www.chymist.com/HAIR%20ANALYSIS.pdf

Try dissolving it in the water first; if you still have grains, you may not have enough MgSO4 in solution for the reaction to go forward.

I did solubility tests again today, and I received much better results. Thanks!

P.S. Are ammonium chloride and Benedict's solution supposed to react in any way? I've heard the mixture is supposed to turn dark blue "almost immediately", but I tested it out today and nothing happened. Is there a different procedure I'm supposed to use other than the regular way of testing for glucose? (add a few drops of Benedict's to the solution w/ the powder, then heat in a hot water bath) I know ammonium chloride is supposed to give off an odor when NaOH is added, but I'd like another way of distinguishing it just to be sure.

[scm424]

My worst area is human hair ids, so does anyone have a really great study tool I could use?

I've mainly focused on distinguishing hair between different species, not between different people, but maybe this page can help, if you haven't already looked at it: http://www.chymist.com/HAIR%20ANALYSIS.pdf

Try dissolving it in the water first; if you still have grains, you may not have enough MgSO4 in solution for the reaction to go forward.

I did solubility tests again today, and I received much better results. Thanks!

P.S. Are ammonium chloride and Benedict's solution supposed to react in any way? I've heard the mixture is supposed to turn dark blue "almost immediately", but I tested it out today and nothing happened. Is there a different procedure I'm supposed to use other than the regular way of testing for glucose? (add a few drops of Benedict's to the solution w/ the powder, then heat in a hot water bath) I know ammonium chloride is supposed to give off an odor when NaOH is added, but I'd like another way of distinguishing it just to be sure.

NH4Cl is supposed to turn dark blue with benedict's solution (some type of copper complex ion forms. [Cu(NH3)4]2+ maybe? Nevertheless, it still is dark blue). It is kind of hard to tell sometimes though. I suggests filling up a test tube with the same amount of water as the NH4Cl solution test tube and then add the same amount of benedict's solution to each test. This way, you can tell if one is more blue than the other.

[salcedam]

P.S. Are ammonium chloride and Benedict's solution supposed to react in any way? I've heard the mixture is supposed to turn dark blue "almost immediately", but I tested it out today and nothing happened. Is there a different procedure I'm supposed to use other than the regular way of testing for glucose? (add a few drops of Benedict's to the solution w/ the powder, then heat in a hot water bath) I know ammonium chloride is supposed to give off an odor when NaOH is added, but I'd like another way of distinguishing it just to be sure.

If you compare the color of ammonium chloride and Benedict's with sucrose/glucose with Benedict's, you will see a definite deeper, darker blue with ammonium chloride. By the way, you compare the solutions with Benedict's WITHOUT heating it. So you just put Benedict's in the solution of ammonium chloride and it'll just be a darker blue than Benedict's with glucose/sucrose. Again, don't heat the solution of ammonium chloride after adding Benedict's. Just see if it's a darker blue than normal.

[Phenylethylamine]

My worst area is human hair ids, so does anyone have a really great study tool I could use?

I've mainly focused on distinguishing hair between different species, not between different people, but maybe this page can help, if you haven't already looked at it: http://www.chymist.com/HAIR%20ANALYSIS.pdf

Try dissolving it in the water first; if you still have grains, you may not have enough MgSO4 in solution for the reaction to go forward.

I did solubility tests again today, and I received much better results. Thanks!

P.S. Are ammonium chloride and Benedict's solution supposed to react in any way? I've heard the mixture is supposed to turn dark blue "almost immediately", but I tested it out today and nothing happened. Is there a different procedure I'm supposed to use other than the regular way of testing for glucose? (add a few drops of Benedict's to the solution w/ the powder, then heat in a hot water bath) I know ammonium chloride is supposed to give off an odor when NaOH is added, but I'd like another way of distinguishing it just to be sure.

NH4Cl is supposed to turn dark blue with benedict's solution (some type of copper complex ion forms. [Cu(NH3)4]2+ maybe? Nevertheless, it still is dark blue). It is kind of hard to tell sometimes though. I suggests filling up a test tube with the same amount of water as the NH4Cl solution test tube and then add the same amount of benedict's solution to each test. This way, you can tell if one is more blue than the other.

This. Definitely this. For relatively subtle color changes, always compare side by side.

And salcedam is correct, you do not need to heat the mixture to see this effect; the reaction between ammonium chloride and Benedict's occurs at room temperature.

[Dragonshark]

NH4Cl is supposed to turn dark blue with benedict's solution (some type of copper complex ion forms. [Cu(NH3)4]2+ maybe? Nevertheless, it still is dark blue). It is kind of hard to tell sometimes though. I suggests filling up a test tube with the same amount of water as the NH4Cl solution test tube and then add the same amount of benedict's solution to each test. This way, you can tell if one is more blue than the other.

This. Definitely this. For relatively subtle color changes, always compare side by side.

And salcedam is correct, you do not need to heat the mixture to see this effect; the reaction between ammonium chloride and Benedict's occurs at room temperature.

Thanks again. I'll have to retry this tomorrow.

[Phenylethylamine]

Thanks again. I'll have to retry this tomorrow.

You're quite welcome.

Only peripherally related: Has anyone else noticed how few people seem to know how to use Benedict's?

At my Regionals last year (and okay, it's Regionals, but still), we were the only team that actually left the test tube with Benedict's (and what turned out to be glucose) in the hot water bath for more than maybe ten seconds. There was one communal hot water bath at the back of the room, and we asked the event supervisors if we could leave our test tube in there for a little while and go back to our lab station; they gave us this surprised/approving look, since apparently nobody else had thought to leave it in there for long enough for this to be relevant. There were a couple teams near the back that saw ours turn orange and got rather worried, since they hadn't found any glucose...

I was familiar with Benedict's solution from doing Food Science years ago, and I know that if you have a food sample that contains a relatively small amount of a reducing sugar, it can take up to ten minutes for the qualitative test to show anything. With pure glucose, it only took a minute or so, but still, you had to wait. Are there some instructions out there that are leading people to believe it's an instantaneous test?

[AlphaTauri]

I was familiar with Benedict's solution from doing Food Science years ago, and I know that if you have a food sample that contains a relatively small amount of a reducing sugar, it can take up to ten minutes for the qualitative test to show anything. With pure glucose, it only took a minute or so, but still, you had to wait. Are there some instructions out there that are leading people to believe it's an instantaneous test?

Perhaps the fact that NH4Cl turns deep blue immediately with Benedict's is leading people to think that glucose will turn orange immediately as well?

Also, does KCl turn green with Benedict's + heat? I've seen it written in our old forensics notes, but I haven't been able to find confirmation nor get the lab time to test it out.

Edit: Although Wikipedia does say that Benedict's can form a green precipitate...

[Phenylethylamine]

I was familiar with Benedict's solution from doing Food Science years ago, and I know that if you have a food sample that contains a relatively small amount of a reducing sugar, it can take up to ten minutes for the qualitative test to show anything. With pure glucose, it only took a minute or so, but still, you had to wait. Are there some instructions out there that are leading people to believe it's an instantaneous test?

Perhaps the fact that NH4Cl turns deep blue immediately with Benedict's is leading people to think that glucose will turn orange immediately as well?

I don't know, I always assumed that use of Benedict's was less well known than using it to test for reducing sugars.

Also, does KCl turn green with Benedict's + heat? I've seen it written in our old forensics notes, but I haven't been able to find confirmation nor get the lab time to test it out.

Edit: Although Wikipedia does say that Benedict's can form a green precipitate...

From a quick google search, I'm seeing that KCl will turn Benedict's green (not a green precipitate, green solution) because it reacts with copper(II) sulfate to make [CuCl4]2- ions, which are green in solution. KF would make a green precipitate, because CuF2 is insoluble and green, but KF is not on the list.

I don't see anything about heat, just that you add aqueous KCl to aqueous CuSO4 (AKA the main ingredient of Benedict's solution).

[salcedam]

I was familiar with Benedict's solution from doing Food Science years ago, and I know that if you have a food sample that contains a relatively small amount of a reducing sugar, it can take up to ten minutes for the qualitative test to show anything. With pure glucose, it only took a minute or so, but still, you had to wait. Are there some instructions out there that are leading people to believe it's an instantaneous test?

Perhaps the fact that NH4Cl turns deep blue immediately with Benedict's is leading people to think that glucose will turn orange immediately as well?

Also, does KCl turn green with Benedict's + heat? I've seen it written in our old forensics notes, but I haven't been able to find confirmation nor get the lab time to test it out.

Edit: Although Wikipedia does say that Benedict's can form a green precipitate...

With respect to the confusion about Benedict's and glucose, I think people just don't know how long to wait because the reaction time can vary and they may have done previous tests where the orange precipitate formed almost instantaneously (perhaps 30 seconds or so). The most I had to wait for a solution of glucose and Benedict's to react was about 4 minutes. Not sure why it took that long...perhaps the water wasn't hot enough...

According to the dichotomous key the Woz has, KCl does turn Benedict's green WITH heat.