Crime Busters B

[christseeker]

Hi Coaches for CB,

In trying to prepare by kids for CB, we have been watching a few useful youtubes on fabric burn tests. Burn test itself seems sufficient to identify whether a fabric is of an animal, plant, or synthetic material. My question is that can we count on a candle/lighter being provided during the competition, or should I continue prep them by testing with HCl, iodine, hydrogen peroxide (I saw these tests suggested in one of the files somewhere online)? The rule says "The supervisor MAY provide candle and matches if fibers are given."

[samlan16]

Hi Coaches for CB,

In trying to prepare by kids for CB, we have been watching a few useful youtubes on fabric burn tests. Burn test itself seems sufficient to identify whether a fabric is of an animal, plant, or synthetic material. My question is that can we count on a candle/lighter being provided during the competition, or should I continue prep them by testing with HCl, iodine, hydrogen peroxide (I saw these tests suggested in one of the files somewhere online)? The rule says "The supervisor MAY provide candle and matches if fibers are given."

Usually, the proctor will give you a candle and a lighter only if hair and fabric is given, and some may be generous enough to provide microscopes as well. For the most part, they understand that identifying fibers by any other method is subjective and may result in points off, so you can count on having something to burn fabric with. As for the HCl method, I have never heard of that before and cannot comment.

(A little caveat here: do not use Bunsen burners to do burn tests. The flame will be too hot, and it will be difficult to differentiate between the fibers.)

[sciolylover13]

Does anyone know how to identify mixtures? This is my 2nd time doing this event (the 1st was in 6th grade, so.... )


Edit: Anyone?

[whovian11]

I would just look at it and test with HCl, Iodine, and water. their not too hard. just don't put too much in of anything in a single thing.

[sciolylover13]

I would just look at it and test with HCl, Iodine, and water. their not too hard. just don't put too much in of anything in a single thing.

I know that, but I was just wondering how to identify them, AFTER testing. Thanks for the answer though!!

[christseeker]

When coaching my kids for CB, they added HCl to sodium acetate, and it fizzed. Notes elsewhere said that it is not supposed to. What is going on?

When water is added to gypsum, ours turned into "oyster poop" color (shown in the link below). Is this always the case?

http://3.bp.blogspot.com/-g5S6Lt3ltjM/U ... G_6181.jpg

[AlphaTauri]

Hmm yeah, HCl + sodium acetate should not fizz to my knowledge... is it possible there was residue from some kind of carbonate in the test tube/container?

I have no idea about the gypsum though, sorry.

[samlan16]

When coaching my kids for CB, they added HCl to sodium acetate, and it fizzed. Notes elsewhere said that it is not supposed to. What is going on?

When water is added to gypsum, ours turned into "oyster poop" color (shown in the link below). Is this always the case?

http://3.bp.blogspot.com/-g5S6Lt3ltjM/U ... G_6181.jpg

Sodium acetate should not fizz. I would recommend thoroughly cleaning your labware by hand, then testing again. (Perhaps the HCl reacts with dishwasher soap that violently, but I don't know how you're cleaning.)

As for the gypsum, I don't know what to say. Could it have been impure, or could it have reacted with residue? Calcium sulfate should retain its color when water is added.

Also, how much gypsum did you use? Be careful about giving your kids too much- proctors usually only give competitors a couple of grams of each sample as though they were collected from a crime scene.

[whovian11]

about the gypsum, I think that you put too much of something in your test. also with sodium acetate it should not fizz but I think, from my memory, mine fizzed too but I'm not sure. after you do the tests and you can't identify something look in any and all sheets you have also check out sonic.org.

[samlan16]

Pure speculation (pun intended), but this chemical distributor lists several impurities regularly found in their sodium acetate. Some of the listed ions, such as phosphate and sulfate, could be in compounds that spontaneously react with HCl. If you used acetate that is not up to food grade or industrial grade standards, this may be what caused your problem.