chemrox
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Testing Ar-flushed apparatus for oxygen
I want to test my inert gas technique and apparatus as I've had some poor yields from some reax that should have been nearly quantitative. I'd like a
relatively cheap synthesis that the only real problem is the need to exclude oxygen. It should be something that takes about 24 hours and doesn't
have to be watched.
I'm not sure this is the right place to post the request but I'd surely be grateful for ideas.
Edit by Chemoleo: more descriptive title
[Edited on 8-3-2008 by chemoleo]
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chemkid
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I don't know if this counts, but get a piece of lithium from a lithium battery and try to preserve it for twenty four hours. If you want instructions
here they are: http://www.theodoregray.com/PeriodicTable/Stories/003.2/inde...
personally mine went just fine without any explosions.
Chemkid
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chemrox
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oh, you mean keeping the metal in the flask without air keeps it from degrading and the quantity is so small that there's no danger of fire. If the
system leaked the flask would survive...
It's a really good idea. Thank you. What's missing is an opportunity to test the addition process. But I take that back. I could suspend the Li
and add liquid down the opposite side. Simple is best. I'm in business.
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not_important
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One commercial test for O2 is based on Indigo Carmine
Indigo Carmine--ASTM D 888-87, Colorimetric Indigo Carmine, Test Method A.
Gilbert, T.W., Behymer, T.D., Castaneda, H.B., "Determination of Dissolved Oxygen in Natural and Wastewaters," American Laboratory, March 1982, pp.
119-134.
Rhodazine D method--(Method developed by CHEMetrics, Inc.) Power Plant Manual, First ed., p. 169 (1984).
ASTM D 5543-94, Standard Test Methods for Low Level Dissolved Oxygen in Water.
http://webpages.charter.net/kwingerden/erhs/aquarium/informa...
Another possibility would be a solution of a Ce(III) salt made slightly alkaline. Oxygen causes the white Ce(OH)3 to be oxidised to Ce(IV), the mixed
oxidation state intermediates are fairly strongly coloured orange-red, going to more of a yellow when fully oxidised.
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UnintentionalChaos
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Even regular indigo should be able to perform an oxygen detecting test. You need some indigo, a reducing agent (typically thiourea dioxide is used)
and some water. Add an escess of indigo powder to a solution of the reducing agent and allow to sit for a few hours so all the reductant has been used
up. Take some of the solution (containing soluble, reduced, "leuco" indigo) from below the surface and above the excess indigo sediment and place in
the flushed out apparatus. Any oxygen present should form an insoluble dark blue scum of indigo powder on the surface of the liquid
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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chemrox
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Thanks a whole lot both of you. Are these procedures making solutions as such or mixtures that one watches the colors? Solutions would probably be
esier to observe .... why I asked.
For the indigo tests... what reducing agents might be used if one doesn't have thiourea? I have formic acid and BH4 ... STAB ... Fe, HCl, urea ...
would sodium formate work?
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garage chemist
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Sodium dithionite works for reducing indigo.
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UnintentionalChaos
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^^I forgot about that. It probably works much faster too.
The reduced form of indigo is water soluble so it will be a solution. The oxidation product is insoluble.
Indigo sulfonate (indigo carmine) however, is mildly water soluble even when oxidized, so any color would be dispersed in the liquid and probably
harder to detect. Since this appears to be intended as a quantitative test (you seem to want a qualitative test), the absorbance of the final solution
could be measured with a colorimeter and used to calculate oxygen content.
[Edited on 10-4-07 by UnintentionalChaos]
[Edited on 10-4-07 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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chemrox
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This gets a little more "quantitative' than I wanted to go. As you say, I'm after a qualitative determination. And it should be vividly clear(if
possible) yes or no as regards O2 leaking in. It could be something sensitive to CO2 as well. There might be more colormetrics there than for O2.
I don't know but I've gotten some direction from you as to what kind of things to read up on. For our work we might find a CO2 sensitive agent useful
too. It would be ideal if the reaction with air were immediate and visible.
[Edited on 4-10-2007 by chemrox]
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UnintentionalChaos
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Barium hydroxide solution? It should cloud at the faintest sign of CO2 dissolved into it.
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chemrox
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That's right I ws going to run my Argon through it to make sure it isn't mixed gas
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chemrox
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outgassing water to make Ba(OH)2 solution
I need Ba(OH)2 solution to check my gasses. Should I distill the water under inert gas, assuming the gas is OK, to keep CO2 out of the test solution?
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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Fleaker
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Couldn't you just vacuum distill it and save gas?
Neither flask nor beaker.
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--The Dark Lord Sauron
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UnintentionalChaos
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| Quote: | Originally posted by chemrox
I need Ba(OH)2 solution to check my gasses. Should I distill the water under inert gas, assuming the gas is OK, to keep CO2 out of the test solution?
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Just boil up some distilled water and add Ba(OH)2. Seal it up in an airtight bottle and let it sit for a while so any small amount of BaCO3 formed
settles, then decant when needed. No need for vacuum or distillation.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Sauron
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I have never heard of testing for O2 like this.
The technique is to evacuate the system, then flush it with N2 or Ar and repeat that purge/flush cycle several times. Finally you leave the system at
slight positive pressure to keep air from diffusing in, your vent is Hg-bubbler or mineral oil bubbler sealed off from the air, and you are ready to
go.
These procedures are well described for lithiation reactions and many other moisture and air sensitive reactions. A quick look at Org.Syn. will
suffice.
Sic gorgeamus a los subjectatus nunc.
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evil_lurker
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You probably already know this, but Ar is a superior shielding gas... supposedly its heavier than O2 and will form a "blanket".
Its also expensive, I got a little 80 cf cylinder and it set me back about $225.
Not all chemicals are bad. Without chemicals such as hydrogen and oxygen, for example, there would be no way to make water, a vital ingredient in
beer.
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Sauron
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For most inert gas procedures, N2 if dry and free from O2 will do almost as well, and is a lot cheaper. But when you need Ar, you need it.
There are inline filters to remove traces of O2.
Sic gorgeamus a los subjectatus nunc.
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Fleaker
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Argon is cheap enough, 20 dollars for 148 cubic feet of it at the welding store. The tank is what is expensive, about 190 dollars from my supplier for
a 148 cu ft tank. They are a few miles down the road, so I am willing to pay this. It is even cheap from Linde, Airgas, or Praxair and they have many
other gases like NH3, SF6, SO2 etc. (usually a business permit is required for those).
Argon from the bottle is typically 99%+, but you can pay for gas that costs more, although usually every additional 9 in purity is 50-70 USD in price.
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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chemrox
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Wow-I'm not paying anywhere near that for the tanks I'm using but the bigger one's on loan. I got a smaller one from HF and upgraded at the welding
store for $23.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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MagicJigPipe
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Did you mean for HF? If you mean from, what is HF?
Also, Ar is the most abundant inert gas on Earth (exept N2 of course) and should be cheaper than it is IMO.
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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chemrox
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HF= Harbor Freight a US outlet for Chicom goods
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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unionised
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"Also, Ar is the most abundant inert gas on Earth (exept N2 of course) and should be cheaper than it is IMO."
Cheaper than it is?
It's already free, you keep breathing the stuff.
What people pay for is removing the other 99% or so of the air and putting it in tanks.
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