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#1
Old 03-16-2001, 10:50 PM
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If you put helium in a balloon, it rises because helium is lighter than air. My question is: what gas could you put into a balloon to make it sink like a stone? What gas is heavier than air?
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Old 03-16-2001, 10:57 PM
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I wish I still had my reference tables from last year's Grade 11 Chemistry class.

Off the top of my head, there's xenon, radon and krypton. I think they're more massive than air.
#3
Old 03-16-2001, 11:07 PM
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Since the density of a gas at any given pressure and temperature depends almost entirely on its molecular weight, any gas with a molecular weight greater than Nitrogen (28) will be heavier than air.
Common gases that are heavier than air include;
Carbon dioxide,Oxygen and propane.
#4
Old 03-16-2001, 11:10 PM
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Carbon Dioxide.

It's pretty cheap to get a sample into a balloon, too. Fill a small bottle half full of bicarbonate of soda. Fill a balloon with vinegar. Put the balloon neck over the bottle, and hold it tightly. Dump the vinegar into the bottle. The balloon will fill with a colorless odorless gas. (Ok, the vinegar will still stink, but that's not the gas we are talking about.) Tie it off.

Now fill a balloon with air. (Just blow it up.) Fill them both to the approximate same size. Drop them. Watch.

Science. (Well, if you take good measurements of everything, and write it all down, with your observations, and get someone else to do the same thing in a different location, and then get a third someone else to design an experiment using a different methodology, and then compare results, it would be science.)
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Old 03-16-2001, 11:37 PM
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Well, um, [silly giggle] air is heavier than air. That is, if all you want is to make a balloon sink. Blow up a balloon and down it goes to the floor, thud, every time.

Hee.

#6
Old 03-16-2001, 11:47 PM
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Let me put this another way...

Is there a known planet where a balloon filled with air from planet Earth would float?
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Old 03-16-2001, 11:47 PM
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Any gaseous element with a greater atomic mass than air will sink. So will gaseous compounds. Propane has a weight of 44.1 g/mole. Ethane is 30.2/mole. These are both heavier. Hope that helps!
#8
Old 03-16-2001, 11:47 PM
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DDG Air weighs the same as air. Therefore the balloon wouldn't sink or rise.

But if you *blew it up*, perhaps the carbon dioxide you expelled into the balloon would be heavier than the *air* and it would sink.
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Old 03-17-2001, 12:06 AM
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You have to factor in the weight of the baloon, too.

I remember that my chem teacher dropped a baloon filled with a very heavy gas. (Xenon?) It dropped rather quickly.
#10
Old 03-17-2001, 12:08 AM
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Re: Let me put this another way...

Quote:
Originally posted by DaveRaver
Is there a known planet where a balloon filled with air from planet Earth would float?
Venus. Its atmosphere is almost entirely CO2.

But to get the balloon to float, you'd have to fill it with a pressure of 90 earth atmospheres so that the balloon doesn't collapse. And make the balloon out of something that won't melt at 450 C.
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#11
Old 03-17-2001, 07:58 AM
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Quote:
Originally posted by samclem
DDG Air weighs the same as air. Therefore the balloon wouldn't sink or rise.

But if you *blew it up*, perhaps the carbon dioxide you expelled into the balloon would be heavier than the *air* and it would sink.
When you breathe out, the concentration of CO2 is higher than what you breathed in, but it's still only a small percentage. In other words, you don't convert all the O2 into CO2. This is why CPR works.

If you inflate a ballon with a pump, it will have the same composition as the surrounding air but it will still sink. The air inside the ballon is under pressure and therefore denser. If you want to see a hovering balloon fill it with helium and wait a day or two.
#12
Old 03-17-2001, 08:11 AM
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Quote:
Originally posted by samclem
DDG Air weighs the same as air. Therefore the balloon wouldn't sink or rise.

But if you *blew it up*, perhaps the carbon dioxide you expelled into the balloon would be heavier than the *air* and it would sink.
DDG is correct. This is an easy experiment - haven't you ever blown up a ballon, and watched it fall to the ground? The weight of the ballon itself if the important factor, but the balloon will also contain air that is slightly pressurized, and thus denser.
#13
Old 03-17-2001, 08:20 AM
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My favorite demonstration experiment is to fill a bucket with carbon dioxide (dry ice, or vinegar/soda), and then blow soap bubbles gently above the bucket. The bubbles are heavier than air, so they gradually descend, but the ones that land in the bucket will float upon the carbon dioxide in the bucket. They bounce, and just rest there. It's fairly dramatic.

Then, you can scoop out carbon dioxide to change the level, or you can lower lit matches into it and watch them be put out at the same level as the bubbles.

It makes the invisible carbon dioxide gas "visible," by indirect means. Kids' imaginations go wild
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#14
Old 03-17-2001, 12:09 PM
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The upper parts of the Venusian atmosphere would have less pressure. However, if the gases involved still adequately obey the perfect gas law under those conditions, the high pressure could be of help, if you could construct a satisfactory balloon shell - the weight differences between corresponding volumes of gasses should be that much higher. PV = nRT.

The Martian atmosphere, what there is of it, is also almost entirely carbon dioxide. Here, the problem is reversed. Pressures are so low that you would need huge volumes to get much lift. You would probably need an enormous balloon to get enough volume in relation to the balloon weight to float it. There is actually some discussion of using balloons on Mars, though the experiments to date have been filled with methanol, vaporized by solar heat to expand the balloon:

http://space.com/scienceastronom...on_000831.html
#15
Old 03-17-2001, 12:50 PM
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Originally posted by Mikahw
You have to factor in the weight of the baloon, too.

I remember that my chem teacher dropped a baloon filled with a very heavy gas. (Xenon?) It dropped rather quickly.
Xenon's atomic weight is about 130. I suspect krypton (atomic weight about 84) would provide an adequate demonstration, too, and might be easier to obtain. Argon is only a bit denser than the air (about 40), and wouldn't be that impressive. Radon is the densest gas known at STP - atomic weight around 220, but you aren't going to be fiddling with balloons full of something radioactive.

At a molecular weight of 58, butane is a heavy gas that everybody is familiar with from butane lighters. I'm sure many of us have filled a beer bottle with butane from a lighter and "poured" it over a candle. I'm not sure that is really a safe activity, so you do it at your own risk.
#16
Old 03-17-2001, 01:29 PM
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Quote:
Originally posted by Mikahw
I remember that my chem teacher dropped a baloon filled with a very heavy gas. (Xenon?) It dropped rather quickly.
My chem teacher went one step further. I recall he inhaled some xenon to make his voice deeper -- to demonstrate the opposite effect of helium. Of course, he then had to stand on his head for several minutes to drain the heavy gas out of his lungs. Needless to say, the class used the downtime non-constructively. Which is exactly what would have happend anyway if the teacher had asphyxiated.

--Grump "noble surprise" y
#17
Old 03-17-2001, 03:31 PM
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Quote:
Originally posted by TheeGrumpy
Which is exactly what would have happend anyway if the teacher had asphyxiated.
For older students, the disaster of Lake Nyos is a powerful image. The idea of a lakefull of carbon dioxide slowly flowing down a river course, silently killing everything in its path, is very impressive.

Hmm. That link is hard to read. I hope it is the right one.
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#18
Old 03-17-2001, 10:46 PM
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I'm reminded of an experiment...

I remember my High School chemistry teacher proved to us that Propane is heavier than air. We made propane bubbles and then set them on fire. . .
The propane bubbles dropped very fast, of course they went up in FLAMES before they hit the ground...
That was some cool stuff!
#19
Old 03-09-2013, 04:38 PM
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Gas Heavier than Air

Sulfur Hexafluoride
#20
Old 03-09-2013, 05:14 PM
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Quote:
Originally Posted by TheeGrumpy View Post
My chem teacher went one step further. I recall he inhaled some xenon to make his voice deeper -- to demonstrate the opposite effect of helium. Of course, he then had to stand on his head for several minutes to drain the heavy gas out of his lungs. Needless to say, the class used the downtime non-constructively. Which is exactly what would have happend anyway if the teacher had asphyxiated.
Uh, and DID he self-asphyxiate? Who did the CPR to revive him after he spent several minutes standing his head to drain his lungs out?

More accounts I read of breathing helium indicate that a breath of He will render you unconscious in 15 seconds or so. Normally, if you take a deep breath and hold it, there's enough oxygen there to sustain you for a minute or more before you pass out. But if you fill your lungs with helium, or whatever other gas, with no O mixed in, you will pass out very quickly.

Or so they say.
#21
Old 03-09-2013, 05:21 PM
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Originally Posted by RM Mentock View Post
My favorite demonstration experiment is to fill a bucket with carbon dioxide (dry ice, or vinegar/soda), and then blow soap bubbles gently above the bucket. The bubbles are heavier than air, so they gradually descend, but the ones that land in the bucket will float upon the carbon dioxide in the bucket. They bounce, and just rest there. It's fairly dramatic.
Now that sounds like one kewl experiment.

Here's the one I saw demonstrated in my 8th grade science class:

Fill a small bucket with CO2 gas. It's invisible, so you just have to take it on faith that the CO2 will just sit there in the bucket, and not instantly completely dissipate.

Now, light a candle. Hold the bucket about a foot above the candle, and pour the CO2 out of the bucket. The candle will go out, thus demonstrating that you can pour CO2 through air.

Just a little safe-n-sane demo of the Lake Nyos incident.
#22
Old 03-09-2013, 06:06 PM
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Originally Posted by zXMonsterz View Post
Sulfur Hexafluoride
Quote:
Originally Posted by Senegoid View Post
Uh, and DID he self-asphyxiate?
Nah.
#23
Old 03-09-2013, 08:42 PM
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Fill a ballon with R12 and it will drop straight to the floor.
#24
Old 03-09-2013, 09:14 PM
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Sulfur Hexafluoride is heavier than xenon, and about the densest gas that's inert enough that you'd want to play with it. There are things like tungsten hexafluoride that are heavier but god-awful reactive with air, water and chemistry teachers.
#25
Old 03-09-2013, 09:23 PM
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What gas is heavier than air?
As those in the Flanders trenches in The Great War would verify, chlorine gas (Cl2) is heavier than air.
#26
Old 03-09-2013, 10:55 PM
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Uh, and DID he self-asphyxiate? Who did the CPR to revive him after he spent several minutes standing his head to drain his lungs out?
In this thread we discussed the heavy-gases-will-pool-in-your-lungs belief, a bit. I believe the chem teacher stood on his head quite unnecessarily.
#27
Old 03-09-2013, 11:53 PM
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Sulfur Hexafluoride is heavier than xenon, and about the densest gas that's inert enough that you'd want to play with it. There are things like tungsten hexafluoride that are heavier but god-awful reactive with air, water and chemistry teachers.
If you want to up the temperature some (168 F), xenon hexafluoride is quite the heavy gas with a molecular weight of 245. I'm guessing a balloon filled with that would hit the floor pretty quickly.
#28
Old 03-10-2013, 12:49 AM
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In Israel during Gulf I (Scuds from Iraq War), the entire populace learned something about heavier-than-air gas, most of whom never gave the matter much thought beforehand, I'm guessing.

It became Topic A in that, by all common sense and proved by experience, War/Missiles=head for bomb shelter. But everyone was lectured over and over again that whatever anticipated gas released from the Scuds would sink. So ixnay on the shelters. It was all the more unnerving to be sitting ducks that way.

Towards the end of the war rumors got out that high defense staff were saying Fuck this, I'm staying in the shelter, and people started following suit. Hell, that's when Scud versus Patriot viewing parties were going on.

Last edited by Leo Bloom; 03-10-2013 at 12:50 AM.
#29
Old 03-10-2013, 12:52 AM
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Nm.

Last edited by Leo Bloom; 03-10-2013 at 12:52 AM.
#30
Old 03-10-2013, 01:48 AM
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Originally Posted by snailboy View Post
If you want to up the temperature some (168 F), xenon hexafluoride is quite the heavy gas with a molecular weight of 245. I'm guessing a balloon filled with that would hit the floor pretty quickly.
It must take quite some laboratory trickery to create xenon hexafluoride, xenon being an inert gas. I know some inert gases can be coaxed into molecules with other atoms by sufficiently contrived laboratory procedures. But it this possible with the heavier inert gases, or only with the lighter ones? And are such compounds stable, or do they decompose promptly?

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#31
Old 03-10-2013, 03:00 AM
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Originally Posted by Senegoid View Post
It must take quite some laboratory trickery to create xenon hexafluoride, xenon being an inert gas. I know some inert gases can be coaxed into molecules with other atoms by sufficiently contrived laboratory procedures. But it this possible with the heavier inert gases, or only with the lighter ones? And are such compounds stable, or do they decompose promptly?
http://en.wikipedia.org/wiki/Noble_gas_compounds

There appears to be more compounds with the heavier noble gases than the lighter ones. There are none for helium or neon. As I recall (and my link probably talks about this but I haven't read all of it), they are quite difficult to make but once made, they're very stable.
#32
Old 03-10-2013, 03:13 AM
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Originally Posted by Senegoid View Post
Uh, and DID he self-asphyxiate?
Yes, and turned into a zombie.




As to the rest, I'm guessing exhaling normally would clear the lungs enough to allow normal breathing, but the headstand is to ensure that all the xenon is gone.
#33
Old 03-10-2013, 03:28 AM
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Originally Posted by snailboy View Post
http://en.wikipedia.org/wiki/Noble_gas_compounds

There appears to be more compounds with the heavier noble gases than the lighter ones. There are none for helium or neon. As I recall (and my link probably talks about this but I haven't read all of it), they are quite difficult to make but once made, they're very stable.
Ignorance fought.

It appears there are a LOT of Xenon compounds, in particular. The linked wiki mentions one that's even easy to create:
Quote:
Xenon difluoride can be produced by the simple exposure of Xe and F2 gases to sunlight; while the mixing of the two gases had been tried over 50 years before in an attempt to produce a reaction, nobody had thought to simply expose the mixture to sunlight.
#34
Old 03-10-2013, 03:33 AM
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Originally Posted by Malacandra View Post
As to the rest, I'm guessing exhaling normally would clear the lungs enough to allow normal breathing, but the headstand is to ensure that all the xenon is gone.
But I don't think it is necessary. Probably not even helpful. Gases in the lungs mix pretty well with every breath, so any xenon in your lungs should be quickly diluted and expelled, assuming you're breathing normal air again.

In this thread I linked to in that previous discussion here, Bored Chemist links to this MRI image of xenon in lungs, which shows that the xenon is evenly distributed throughout the lungs.
#35
Old 03-10-2013, 03:47 AM
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Quote:
Originally Posted by RM Mentock View Post
My favorite demonstration experiment is to fill a bucket with carbon dioxide (dry ice, or vinegar/soda), and then blow soap bubbles gently above the bucket. The bubbles are heavier than air, so they gradually descend, but the ones that land in the bucket will float upon the carbon dioxide in the bucket. They bounce, and just rest there. It's fairly dramatic.

Then, you can scoop out carbon dioxide to change the level, or you can lower lit matches into it and watch them be put out at the same level as the bubbles.

It makes the invisible carbon dioxide gas "visible," by indirect means. Kids' imaginations go wild
That's a really neat way to demo it. The less dramatic way was to pour it over a lit candle to put it out. Seeing it as a boundary layer of gas makes it stand out.

Last edited by Magiver; 03-10-2013 at 03:47 AM.
#36
Old 03-10-2013, 06:09 AM
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As to the rest, I'm guessing exhaling normally would clear the lungs enough to allow normal breathing, but the headstand is to ensure that all the xenon is gone.
Plus, it's more dramatic!

"Mom, my chemistry teacher inhaled this heavy gas that made his voice sound really deep."

vs.

"Mom, my chemistry teacher inhaled this heavy gas that made his voice sound really deep, and then he had to stand on his head to exhale all the gas so he wouldn't die!"
#37
Old 03-10-2013, 08:01 AM
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But I don't think it is necessary. Probably not even helpful. Gases in the lungs mix pretty well with every breath, so any xenon in your lungs should be quickly diluted and expelled, assuming you're breathing normal air again.

In this thread I linked to in that previous discussion here, Bored Chemist links to this MRI image of xenon in lungs, which shows that the xenon is evenly distributed throughout the lungs.
Understood - my point was that even if it didn't work this way, your lungs wouldn't be full of xenon after breathing out once, and any reduced lung capacity would be a nuisance rather than life threatening.

Interesting to note, while I was looking up how expensive this stunt might be (xenon being pretty scarce stuff) that xenon's actually an effective anaesthetic, and not merely an asphyxiant. That's kinda counter-intuitive for a noble gas.

Last edited by Malacandra; 03-10-2013 at 08:01 AM.
#38
Old 03-10-2013, 08:43 AM
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So are there any liquids lighter than the heaviest gas? Could I have a bucket with a light liquid floating on a heavy gas?
#39
Old 03-10-2013, 08:49 AM
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No - there's about two orders of magnitude difference between liquid densities and gas densities (at standard temperature and pressure); that is, you're weighing liquids in hundreds of grams per litre, minimum, and gases in grams per litre.
#40
Old 03-10-2013, 09:10 AM
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Originally Posted by DaveRaver View Post
Is there a known planet where a balloon filled with air from planet Earth would float?
not a planet, but on titan the air is a lot denser than on earth, so any balloons would float up (and the gravity is a lot lighter too, so you could conceivably float using a bunch of earth air balloons)
the venusian atmosphere is a lot denser too, but the balloons would probably cause the air to combust and/or be crushed by pressure
pretty much the same thing on jupiter/saturn/neptune/uranus below certain altitudes

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#41
Old 03-10-2013, 09:13 AM
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So are there any liquids lighter than the heaviest gas? Could I have a bucket with a light liquid floating on a heavy gas?
not exactly in the way you wanted, but if you splash liquid nitrogen over warmer things, like your hand, the little droplets will float above it because they'll be constantly exuding nitrogen gas which gives them a cushion (a bit like a hovercraft)
#42
Old 03-10-2013, 09:29 AM
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not a planet, but on titan the air is a lot denser than on earth, so any balloons would float up (and the gravity is a lot lighter too, so you could conceivably float using a bunch of earth air balloons)
the venusian atmosphere is a lot denser too, but the balloons would probably cause the air to combust and/or be crushed by pressure
pretty much the same thing on jupiter/saturn/neptune/uranus below certain altitudes
Except that Titan's atmosphere is mainly nitrogen, and the only reason why it's denser at the planet's surface is that the pressure is higher. But if you take a balloon there then it too will be subject to the same pressure, and the air in it will be just as dense as Titan's nitrogen. The gas giants have a lot more hydrogen, methane and ammonia than Earth, so a less dense (per pressure) atmosphere than Earth, meaning once again that a balloon full of an 80:20 nitrogen/oxygen mix would still be heavier than the local "air".
#43
Old 03-10-2013, 09:57 AM
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If you want to up the temperature some (168 F), xenon hexafluoride is quite the heavy gas with a molecular weight of 245. I'm guessing a balloon filled with that would hit the floor pretty quickly.
Yeah, but that's cheating a bit; it's got to be a gas at standard temperature and pressure. Otherwise any substance that vaporizes at incandescent temperatures could be a contender.
#44
Old 03-10-2013, 11:00 AM
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If you put helium in a balloon, it rises because helium is lighter than air. My question is: what gas could you put into a balloon to make it sink like a stone? What gas is heavier than air?
two minor points regards the discussion. Xenon is incredibly expensive and difficult to find. I doubt a HS or college or research facility would play with it.

Argon, on the other hand, is one of the minor components of air and is, when separated, significantly heavier than 'air'.

Case in point. A place I worked almost had a fatality because they had a compressor in a low area inside the plant that was converted to pumping argon gas flashing off the liquid argon storage tank (the plant made, among other things, mixes of argon with other gases for various welding purposes). Compressing the flashoff into receivers, then using it to equalize with evacuated cylinders ready to fill would save the expensive argon from being wasted.

The plant manager was inspecting the compressor because someone had reported a leak in the piping between compression stages... The leak was enough that it had filled the low area around the machine with mostly argon. He passed out and a worker noticed him and went in to see what was wrong. He passed out. The third person to come along realized that two men down meant a hazardous atmosphere and he sounded the alarm. Another man held his breath and went in to drag his buddy part way out. Another man did the same for the manager. After several tries, and some wooziness, they succeeded in getting the men out of the low area and reviving them.
#45
Old 03-10-2013, 01:54 PM
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two minor points regards the discussion. Xenon is incredibly expensive and difficult to find. I doubt a HS or college or research facility would play with it.

Argon, on the other hand, is one of the minor components of air and is, when separated, significantly heavier than 'air'.

....
Nitpick - Xenon and Krypton are produced the same way Argon is - fractional distillation of liquid air. However, their concentrations are much lower - xenon is a REALLY "minor" component (Xenon is about 0.09 parts per million by volume, as opposed to about 9300 for Argon). Hence, yeah, it's expensive. They also have to do additional distillation steps to extract xenon and krypton - they are initially trace "contaminants" in the oxygen fraction. If they weren't commercially valuable, I suspect they would leave them there.

A commonly quoted price for xenon seems to be about $120 per 100 grams. I suspect that's the price you would pay through a scientific supply house for fairly small quantities. Not prohibitive for use in classroom demonstrations, but you're spending several dollars to fill a small balloon with it.
#46
Old 03-10-2013, 02:28 PM
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Just throwing this in here because of turn towards processing of noble gases. Everybody in my introductory chemistry course reading this (were any of those words true) is thinking the obvious question: so what's up with Kryptonite?

From the long and detailed Wiki on the subject:
Under standard chemical naming procedures, the -ite suffix of kryptonite would denote an oxyanion of the element krypton. However, krypton is a noble gas that forms compounds only with great difficulty, and such an oxyanion is not known. Nevertheless, the University of Leicester presented the Geological Society with krypton difluoride to commemorate the 70th anniversary of Superman.
No oxyanion: correct?
Krypton diflouride: hard to make? Actually used for anything anywhere?
What would lead the University of Leicester guys to choose Krypton diflouride as being the most Kryptonite-y?*


*It's also a crying shame that ferners had the wherewithal to do this and not 'Mercuns.

Last edited by Leo Bloom; 03-10-2013 at 02:29 PM.
#47
Old 03-10-2013, 04:27 PM
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Originally Posted by Malacandra View Post
[X]enon's actually an effective anaesthetic, and not merely an asphyxiant. That's kinda counter-intuitive for a noble gas.
Not in the least. Anesthetic ability for these sorts of substances is directly correlated with its fat solubility. It works exactly like nitrous oxide. No chemical reactivity required.

So no high school demos with Xe. SF6 is typical.

Last edited by Ruken; 03-10-2013 at 04:29 PM.
#48
Old 03-10-2013, 06:09 PM
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Yeah, but that's cheating a bit; it's got to be a gas at standard temperature and pressure. Otherwise any substance that vaporizes at incandescent temperatures could be a contender.
Yeah, it could be considered cheating which is why I made sure to mention the boiling point. However, it's not so hot that the experiment couldn't be done practically (if you could find enough of the chemical). The balloon should be alright at that temperature and I've heard of humans surviving when temporarily exposed to it or you could just take it out of an oven and quickly drop it. I figured it was worth a mention.
#49
Old 03-10-2013, 06:23 PM
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A balloon filled with air on Venus would float. If you float it at the level in the atmosphere where the temperature is about the same as that found on Earth, the internal pressure will be around 1 atmosphere. That makes the atmosphere of Venus the second most habitable location in the solar system.
See 'Colonisation of Venus' by Geoffrey Landis
http://ntrs.nasa.gov/archive/nasa/ca...2003025525.pdf (pdf)

Last edited by eburacum45; 03-10-2013 at 06:23 PM.
#50
Old 03-10-2013, 10:20 PM
Member
Join Date: Dec 2002
Location: San Diego, CA
Posts: 22,743
Quote:
Originally Posted by samclem View Post
DDG Air weighs the same as air. Therefore the balloon wouldn't sink or rise.

But if you *blew it up*, perhaps the carbon dioxide you expelled into the balloon would be heavier than the *air* and it would sink.
Also, compressed air weighs more than air at ordinary "room pressure." So when you fill a stretchy rubber balloon, you have to blow hard (hey, I'm good at that) and the air is now compressed. So that, too, is part of why the balloon falls to the ground.

(You also have the weight of the rubber to contend with...)
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