Science Crime Busters B

[lakeSUPERIOR]

does anyone know what kind of mixtures are most common for SCB? thanks!!

no mixtures are much more common than others, but like haven chuck said they are likely to give you very different substances together, so you can tell them apart better. Also, as stated in the rules they cannot give you a mixture w/ vitamin C, sodium acetate, or yeast

[Phenylethylamine]

what is a good strategy for identifying mixed powders?

The easiest are ones that are a crystalline and a powder (i.e., sugar and flour. I think there were a good three or so of those at Nats last year, which was set up as a "cupcake-baking competition"... complete with the logical set of powders that would be found there, namely, lots and lots of flour and sugar and flour/sugar mixtures). Those can typically be figured out with just observation, and then the typical reagent tests to see what the powder is.

Anything more complex than that, I've forgotten whatever tricks I knew

[icyfire]

How do you tell distilled water and Hydrogen Peroxide apart?

[lakeSUPERIOR]

You have to be able to test with the regents. How else would you be able to tell H2O and H2O2 apart.

If you shake them, the H2O2 (hydrogen peroxide) will make bubbles, water doesnt

[haven chuck]

There is also a very definitive method using iodine. If you put about 3 mL of the liquid in a well, put in 1 or 2 drops of iodine, and then stir for 2 seconds, H2O2 will bubble a lot after about 30 seconds (no need to stir for that long, just wait), while H20 will not. I'm not sure if it works better than lakeSUPERIOR's method (I've never tried his), but it's just another approach.

[robotman]

You have to be able to test with the regents. How else would you be able to tell H2O and H2O2 apart.

If you shake them, the H2O2 (hydrogen peroxide) will make bubbles, water doesnt

I thought that after a period of time H202 will lose its ability to bubble when shaked

[fmtiger124]

I was always taught what Lake Superior said....but perhaps robot is right I wasn't in charge of liquids but I remember it never working too well

[icyfire]

Okay, so the iodine will not immediately react with the H2O2 but will bubble after around 30 seconds?

[Phenylethylamine]

Okay, so the iodine will not immediately react with the H2O2 but will bubble after around 30 seconds?

Thirty seconds, maybe longer. It depends on how old the hydrogen peroxide is. There have been times in competition when we've waited and waited, finally deciding all the samples must be water- and then like five minutes later, one of them starts bubbling. It's a delayed reaction, and the length of the delay can vary quite a lot.

[lakeSUPERIOR]

it's good to know both strategies, cuz both have their problem

depending on what type of container the liquid is given it it might be hard to shake/see the bubbles