The Vespiary
The Hive => Methods Discourse => Topic started by: TheBlindGenius on April 15, 2002, 11:19:00 PM
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SWIM would like to get an oxygen tank to use for the wacker O2. His question is what size oxygen tank is needed for each wacker. Of course it depends on a few things, so if bees could include how much safrole their friends were using, how big the SRV or container was, etc., it would be appreciated. along Swim could just get a huge one but they are more expensive and harder to hide ;) . He wants the smallest one that can be used for his purposes but not so small that it runs out halfway through a wacker O2.
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This is a simple calculation. If you can't figure this out yourself then you should be doing something else instead of posting in the Methods Forum - reading a high school level chemistry book would be a good start.
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No actually it is not obvious. PV=NRT does not work because the vessel loses pressure as the reaction goes along, therefore you can't just plug in the pressure, volume, .08205, and temperature to get the moles and then figure out how many liters that is. Also, the temperature changes as the reaction goes along, so you can't plug in T either! i'm a second year Chem major, i know something about chem. ;)
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You can't just plug it in.
You must master the ever elusive skill of SUBTRACTION!!!
I know thats challengeing but we have confidence in you...
You can do it!!!
Those who give up essential liberties for temporary safety deserve neither liberty nor safety
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It can't be done by simple subtraction. The temperature is a variable that is constantly changing. Also, you wouldn't subtract to compensate for the pressure drops, you would add. IF the temp was constant it could be done. you would ADD the total uptake of O2 up and plug it into PV=NRT. But since T is not constant you would have two variables, N and T. Am i right or no?
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Time 1, initial
N1=P1V1/RT1
Time 2, say 1 hour
N2=P2V2/RT2
Total Moles O2 taken up at time 2 = N1-N2
Repressurize step 3
N3=P3V3/RT3
Total moles of O2 added upon repressurization = N3-N2
Now keep doing this and then at the end you add up your totals for the mole taken up.
You may want a new user name cause I'm not sure that one suits you :P
LOL
Those who give up essential liberties for temporary safety deserve neither liberty nor safety
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Thanx. But why the ball-busting? LOL ;) Gen Chem was 1 1/2 years ago! Hey wait, the DMF/O2 wacker writeups by KrZ and Grouch don't give the temperatures at each time. Grouch just says warm, hot, etc. So I guess I gotta do it myself and take the temps to do the calculations. :( Unless of course, someone is cool later today and just tells me what size tank they use! ;D Oh well, thanks anywayz
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A 55cubic tank cost you around 100.00 will last you a long time more than you need. Tank is easy and cheap that DMF wacker will drive you crazy. Hope youve done it before using that much reactants otherwise it will be an expensive headahce. Better have a big reactor-non metallic also.
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The size tank will depend on how many moles of oxygen you need, if the oxidation goes 1/1 ect, I don't know the stoichiometery for sure. With that info it is an easy calculation, none of the temperature shit matters. You will only use that stuff to "monitor" the reaction. I would suggest getting 2 or 3 times the amount you "theoretically" need. Even that probably won't bee enough.
Its obvious you don't have much lab experience.
NOTHING EVER WORKS LIKE YOU INTENDED, Lol the sick truth of experimental work. Well maybe pros can avoid this but believe me, most newbee's will have problems, many problems.
hehehe
Have fun :)
Those who give up essential liberties for temporary safety deserve neither liberty nor safety
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You do not heat the DMF wacker. Heat is generated by the reaction. Excess heat will most likelly cause side ractions that will lead to failure. Dont know of anyone who actually monitered actual temp of it. And were you planning to just measure outside of vessel for reading? Not very practical for this one. This is not one for new bees-better try another one first
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True swim doesn't have much cland. lab experience (nano-meth and saf. dist. so far). However, I never said the reaction is heated. I said as the reaction goes on T goes up. Second, what do you suggest, the p-benzo wacker? SWIM thought about that one first but p-benzo is way more expensive than O2 and may be watched. Also, judging by the literature, it seems like as long as you use lots of catalyst and use a glass or polypropylene vessel, the O2 is almost impossible to fuck up. BTW, swim would prob. not try to do more than 350 g saf. at a time, the 2 kg thing was purely theoretical and phrased incorrectly. What swim meant was basically it would suck if someone didn't know how much O2 was needed and tried 2 kg and ran out halfway. That would really blow. ::)
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The modified performic is much easier for those who haven't a great deal of experience, air alone has always worked fine in the SRV as long as shaking was adequate :)
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