Science Crime Busters B

[prelude to death]

Arrowwolf: Check out the Crime Busters Wiki if you need more help, because I recently editted it to put some stuff about the competition in. There's a lot of info and some hints and warnings about the competition there, so check it out if you have some time.

Also, I'd warn you to be careful of time management. Practice with only maybe 45 minutes max, since supervisors will most likely use some time explaining. For some odd reason, the competition always seems to run a LOT faster than when you're practicing, so be aware. If you set yourself with 30 minutes for unknowns, then only use 30 minutes for unknowns. If you drag on too long on one section, keep in mind that you'll have to speed up to make up time in another section.

[Arrowwolf]

Thanks sooooooo much for the advise!! Gonna check it now

[icyfire]

in a mixture of baking soda and alka seltzer, how would tell that there is baking soda in the mixture?

[prelude to death]

Wow.. that's a hard one... Sinco both of their pH values are around the same number, the pH would obviously be a base, right? The next thing to do is look at the crystals. But they are both powdery/sort of grainy substances, right? For me, the Alka Seltzer bubbles with iodine and also sort of separates when mixed. And if I can recall correctly, I THINK baking soda clumps and then pastes, sort of like blood when iodine is in it. So maybe, I'm guessing that maybe there will be slight bubbles with iodine, but it will also clump and paste? If worse comes to worse, and you can't identify the substance, then you could just guess.... Don't waste your time on that mixture (if you see it at the competition) and instead miss a bunch of other easy parts, like the metals and liquids or the other easier non-mixture substances. Or again, you could try to experiment with a lot of common or possible mixtures and start learning some unique characteristics of each one. However, the above is only my guess on what will happen, since I don't ever recall ever being given/testing a mixture of baking soda and alka seltzer before. Good question. I will have to find out sometime....

[willowmist]

This is probably a stupid question, but for plastics, will they provide us with the burnt plastic, or tell us information about what was happening as the plastic was being burnt? In the rules, it says "No burn test allowed but burn results may be provided." Please tell me that I haven't been misinterpreting that sentence for the whole time...

[prelude to death]

Uumm... actually, I don't think that's a really stupid question..... because I actually don't know the anwer to that one. I've only been to one Regionals competition (this is my first year), and all they did was give us the substance of the plastic. Basically, all my partner and I did to identify it was use the stuff that's on the Crime Busters Wiki. They didn't give us stuff for the veggie oil and isopropyl alcohol method and stuff, and they didn't give us a burn test or even burn results, so yeah. Good question. I never thought of that before. I'd say to contact your Regionals (if you haven't had it already) Director or whatever or the State people. If they don't answer you in time for the competition, you should be prepared for both.

[dholdgreve]

This is probably a stupid question, but for plastics, will they provide us with the burnt plastic, or tell us information about what was happening as the plastic was being burnt? In the rules, it says "No burn test allowed but burn results may be provided." Please tell me that I haven't been misinterpreting that sentence for the whole time...

No stupid questions here! I've run this event, as well as forensics several times. I've provided multiple density liquids, but frankly there is just not enough difference in some of the polymer densities to yield absolute results with these tests. I sent away for the standard polymer sample packets, and many of the posted physical characteristics of the polymers don't match what was shipped. The information says clear, the actual color was opaque white... etc. The only chance the average team has of getting these right is if the Event Coordinator actually provides the burn test results... Beyond that, take a guess and move on... it's not worth wasting any more time on than that. Mind you, the rules do not require him to provide these, but if he doesn't, don't waste any time trying to do some sort of meaningful analysis... there is none with the material you are allowed. Guess and move on to an area that you CAN analyze. If you only have 10 minutes to spend, spend it writing a meaningful and well conceived essay as opposed to the polymers... WAY MORE points there!

[dholdgreve]

Wow.. that's a hard one... Sinco both of their pH values are around the same number, the pH would obviously be a base, right? The next thing to do is look at the crystals. But they are both powdery/sort of grainy substances, right? For me, the Alka Seltzer bubbles with iodine and also sort of separates when mixed. And if I can recall correctly, I THINK baking soda clumps and then pastes, sort of like blood when iodine is in it. So maybe, I'm guessing that maybe there will be slight bubbles with iodine, but it will also clump and paste? If worse comes to worse, and you can't identify the substance, then you could just guess.... Don't waste your time on that mixture (if you see it at the competition) and instead miss a bunch of other easy parts, like the metals and liquids or the other easier non-mixture substances. Or again, you could try to experiment with a lot of common or possible mixtures and start learning some unique characteristics of each one. However, the above is only my guess on what will happen, since I don't ever recall ever being given/testing a mixture of baking soda and alka seltzer before. Good question. I will have to find out sometime....

OR... what if you placed 1 cc of the mixture into a test tube. Add 3 ml of water... it fizzes... now you know you have alka-seltzer... let it fizz out completely... Once the fizz is completely gone, slowly add another 2 ml of water without disturbing any remaining sediment... no fizz? great! now add a couple of drops of HCl... it fizzed immediately? identifies a soluble carbonate, right? - Baking Soda... Well delayed fizz {5 to 10 seconds) may indicate the presence of an insoluble carbonate that settled out of the water and is now at the bottom of the tube... CaCO3... No fizz at at all, but sure there was no crystal in the mixture? May be CaSO4.

Since switching the CaSO4 from Plaster of Paris to Gypsum this year, it makes the clean-up much easier, because true gypsum won't get hard like plaster when added to water... it already has set up, and been reground... Gypsum is the end product of set Plaster of Paris... in fact, if you crunched it up and put it in an oven overnight, it would turn back into Plaster of Paris by driving off the added water, and would again harden when water was added to it.

[willowmist]

Prelude, so you mean that you separated the plastics into the two groups and then identified the plastic using clarity and such? Do you know if you got it correct? I've looked at several online sources, but they all seem to disagree as to the clarity of the plastics. I've also looked at samples that my coach bought a while ago, but those results also disagree, like dholdgreve said... Is the information on the Wiki reliable and accurate?

And assuming that they only give you the burnt plastic as opposed to the observations while the plastic was burning, then how would you identify PETE and PVC, considering their similar densities? The Wiki says that PVC is never transparent, but I read on some websites that PVC is clear...

Also, dholdgreve, as an event supervisor, would you interpret "burn results" as the actual, tangible, burnt plastic, or as the observations about the flame test? I will also keep your advice in mind-- it is true that plastics are tricky (at least for me), and time would be better spent working on the analysis.

[prelude to death]

Err, well, I don't know if I got it correct or not, but I do know that my partner and I placed 3rd in the event.... >.<

I don't know about your kit, but the one that my coach gave me was pretty accurate... and when I tested them using the "more unreliable" method, I managed to identify them correctly, with minimal guessing and stuff. Actually, the best way to identify the plastics is still the "better" way with vegetable oil, etc. for me, although the supervisor may not provide that stuff.

As to the accuracy of the Wiki, I'm not entirely sure, since I have only editted a little bit of it. I don't know who added the information about the plastics. I also don't know if anyone has really actually verified any of the information to be true... (I guess I've always taken the Wiki information as for granted and always true.... Good point. >.<)

As for PETE and PVC, according to the Wiki, PVC is also slightly rubbery.... so maybe, texture (if you are allowed to touch the actual tangible substances)?