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Author Topic: Why Does CO2 Escape From An Enclosure More Easily Than Air?  (Read 61234 times)

Offline Peter Ridley under another name

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I am following up on what Pete Ridley was asking about regarding the size of the different air molecules http://www.thenakedscientists.com/forum/index.php?topic=38675.0. I think that most of us know that ordinary party balloons filled with He deflate more quickly than ones we blow up ourselves because the He molecule is smaller than other gases in the air and escapes more easily through pores in the usual latex rubber balloon. I found a question that was asked a couple of years ago about CO2 seeming to escape from a latex balloon even faster than He does http://www.natscience.com/Uwe/Forum.aspx/chem/9671/carbon-dioxide-filled-latex-balloons.

The discussion there wandered off elsewhere without really answering the original question, a bit like what happened to Pete Ridleyís question here, but one person did give a link to a book
Quote
Irwin and Rippe's intensive care medicine
http://books.google.com/books?id=IhDFIj-PoucC&pg=PA48&lpg=PA48&dq=balloon+latex+diffuse+rapidly+co2+OR+carbon-dioxide&source=web&ots=_Ib_fjHAbh&sig=jf7hwFKOF9x_%3Cbr%3Erx89W2c5UAZ3BDw&hl=en&ei=UXePSaPrOYzQMcORoZEL&sa=X&oi=book_result&resnum=5&ct=re%3Cbr%3Esult#v=onepage&q&f=false that says on page 48/49
Quote
carbon dioxide defuses through a latex balloon at a rate of approximately 0.5cc per minute

I decided to try a similar experiment with balloons, filling one with CO2 from vinegar and baking powder (bicarb) and blowing up the other by mouth. Although I havenít done this in a properly scientific way my simple experiment has shown that on both occasions when I filled two apparently identical latex balloons to about the same size (about 120mm diameter) the one filled with CO2 shrank to less than 100mm in a couple of days while the one that I blew up stayed almost unchanged. That gives a CO2 diffusion rate through the balloon of about 1cc/min.

When I get my hands on a CO2 bottle Iíll do a more scientific experiment and record the conditions and results carefully but in the meantime can anyone explain why CO2 seems to escape through a continer when ordinary air doesnít. In his comment on the 20th April Pete Ridley talked about Professor Nisbett having trouble storing CO2 but not CH4 and that CO2 was like a needle http://www.thenakedscientists.com/forum/index.php?topic=38675.50 so maybe shape as well as size is important.



 

Offline CliffordK

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Why Does CO2 Escape From An Enclosure More Easily Than Air?
« Reply #1 on: 27/05/2011 18:57:54 »
Very interesting.

I would have guessed that Methane or Ethane being non-polar would be a problem. 

Perhaps they are right that CO2 has a linear structure "like a needle", whereas substances like water have a V shape, and methane would have a tetrahedral shape.

If I was doing the testing, I might compare a mono-substituted halo-methane such as floromethane or bromomethane to methane.

You might also try Argon.  I have a tank of that somewhere around here so I might be able to test it.
 

Offline Peter Ridley under another name

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Why Does CO2 Escape From An Enclosure More Easily Than Air?
« Reply #2 on: 27/05/2011 20:07:24 »
Hello Clifford, I have no idea what a ďmono-substituted halo-methane such as floromethane or bromomethaneĒ is or how to get or make some Argon so if you do the experiment please let me know what happens. I thought of trying methane using natural gas but as that other experimenter said it is too low a pressure to blow up a balloon. The CO2 is easy and cheap.

I found another reference to balloon catheters, this time comparing CO2 and He as the shuttle (fill?) gas. The book
Quote
Clinical application of the intra-aortic balloon pump
http://books.google.co.uk/books?id=43PX87dkJEoC&pg=PA76&lpg=PA76&dq=%22balloon+catheter%22+CO2+gas&source=bl&ots=wTCxyDvQFR&sig=6wdKgWFnpRL6U9_RsPqZbrUMsyw&hl=en&ei=KrHfTcKUMMmr8QP5oYyQCg&sa=X&oi=book_result&ct=result&resnum=3&sqi=2&ved=0CDMQ6AEwAg#v=onepage&q=%22balloon%20catheter%22%20CO2%20gas&f=false comments on how He-filled catheters need more frequent purging and refilling and it says on page 76 that ďrate of helium loss 1cc per hourĒ, compared with the rate for CO2 of 30cc/hour quoted in the other book that I linked to previously.

It talks about the size of the percutaneous balloon catheters of 9.5F and 8.5F where F is about 1mm circumference http://en.wikipedia.org/wiki/Foley_catheter so I see that my previous comparison of the leakage rate for my CO2-filled balloons with that in a balloon catheter is invalid, however, those two comparisons for CO2 and He in balloon catheters are interesting because they show that He diffuses through the latex twice as fast as does the CO2.

I looked at those gas molecule diameters that Pete Ridley quoted in his comment on 14th April
Quote
Quickly comparing collision*  v kinetic** diameter (in Ň) for the molecules of atmospheric gases of interest to paleo-climatologists, N2 (3.8 v 3.6), O2 (3.5 v 3.5), Ne (2.8 v 2.8), CO2 (3.9 v 3.3), CO (3.7 v 3.8), CH4 (3.8 v 3.8) Ar (3.5 v 3.4), He (2.6 v 2.6), Kr (3.7 v 3.6), Xe (4.0 v 4.0)
http://www.thenakedscientists.com/forum/index.php?topic=38675.0. If heís right with those then there may be some evidence from these balloon experiments and medical use of balloon catheters that it is correct to use kinetic rather than collision diameter when considering this diffusion of air molecules through tiny pores like those in a balloon.
Looking at those diameters for CO2, He and the main atmospheric gases N2, O2 and Ar suggests that if collision diameter is the one to use then a balloon filled with CO2 would stay up longer than one filled with air and much much longer than one filled with He. On the other hand if the right one to use is kinetic diameter then weíd expect the air-filled balloon to say up much longer than the CO2 balloon and the He balloon to go down more quickly than either.

Another thing that I notice is how similar are the sizes of He and Ne (2.6 and 2.8) which makes me expect that they will both diffuse out of a balloon at a similar rate. The difference between the size of CO2 (3.3) and He (2.6) is about the same as the difference between O2 (3.5) and Ne (2.8). Because He diffuses about twice as fast as CO2 according to those two catheter books Iíd expect Ne to diffuse about twice as fast as CO2 so is there any evidence that it does so?

Looking at the comment by Pete Ridley on 17th April http://www.thenakedscientists.com/forum/index.php?topic=38675.25 he quoted from a paper http://icebubbles.ucsd.edu/Publications/Huber_closeoff_EPSL2006.pdf
Quote
For smaller gas species (mainly He and Ne) the fractionation factors are linearly correlated to the molecule size
In the other paper http://icebubbles.ucsd.edu/Publications/closeoff_EPSL.pdf that was used as the main reference there they said ďNe is fractionated 34Ī2 times more than O2Ē so Iíd expect CO2 to be fractionated around 15 times more than O2 based only on size but shape might also play a part. The picture that is shown in Figure 3 of that paper looks like three balloons very close to each other. If those balloons have air in them wonít the smallest gases like He, Ne and CO2 diffuse out of the lowest into the higher ones and the other air gases like N2, O2 and Ar stay behind in the balloons? You said about trying methane but looking at the different sizes I wouldnít expect it to be much different to air, with little loss from the balloon compared with CO2 or He but it would be interesting to know what Ar does because it has a similar size to CO2 if you use kinetic diameter like Pete Ridley said.

The rudimentary experiment that the other person and I did suggest that the balloons with CO2 in them go down because the molecules are smaller than those of the main air gases. If that is the reason then it seems that kinetic diameter should be used and this might be the answer to my question here, but am I right or not? Also, arenít those bubbles in ice that Pete Ridley was arguing about similar to balloons, with tiny pores in them like in latex. Maybe he was right about what he said because Professor Wolff said on 2nd May
Quote
I think that none of us has a definite molecular-level understanding of the physical process occurring at closeoff, and it would be great if someone can do the experiments in the lab to understand that better
so does this kind of experiment with balloons help at all, like yor_on asked about on 19th April.
« Last Edit: 27/05/2011 21:47:47 by Yelder »
 

Offline CliffordK

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Why Does CO2 Escape From An Enclosure More Easily Than Air?
« Reply #3 on: 27/05/2011 20:28:42 »
I use Argon with my welder.  I should be able to setup an experiment easily enough.  I am just lacking balloons.

I don't have any natural gas (methane) in my house, although I may have a little propane somewhere.

Methane basically looks like:

   H
    |
H-C-H
    |
   H

A halo-methane would look like:
   H
    |
H-C-F
    |
   H

or

   H
    |
H-C-Br
    |
   H

But, acquiring it would be a problem, although there are halo-substituted alkanes used in refrigerants. 

Carbon Dioxide is unique as it is a linear molecule.

  :O=C=O:

Whereas Water is a V shaped molecule.


H     H
  \  /
   O
   ..

I am using the colon (:) and periods (..) to indicate unshared electrons.

I'll let yo know if I get an argon balloon experiment running.

I  believe that O2 looks like    :O=O:  and N2 looks like   N≡N

so I am surprised it is so different from the CO2.
« Last Edit: 27/05/2011 20:32:26 by CliffordK »
 

Offline Peter Ridley under another name

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Why Does CO2 Escape From An Enclosure More Easily Than Air?
« Reply #4 on: 27/05/2011 21:52:42 »
Hello Clifford thanks for that explanation of those
Quote
ďmono-substituted halo-methane such as floromethane or bromomethaneĒ
things and for suggesting a shape for N2 and O2.

I've made a few changes to my previous post as I had mixed up some of my thoughts about expected diffusion rates for different gases.
 

Offline Peter Ridley under another name

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Why Does CO2 Escape From An Enclosure More Easily Than Air?
« Reply #5 on: 28/05/2011 18:30:35 »
The latest state of my balloon experiment is that after another day (thatís three altogether) there has been no change in the size of the balloons. I was surprised at this and can only put it down to the fact that the pores in the latex of both air-filled and CO2-filled balloons are too small for the trapped molecules to escape. Is it likely that when first blown up the pores were at a size that allowed through the smaller (assuming that kinetic not collision diameter is relevant) or needle-shaped CO2 molecules but not the larger N2, O2 and Ar molecules?

Maybe there is another explanation but if not then would this not give support to the argument made by Pete Ridley http://www.thenakedscientists.com/forum/index.php?topic=38675.0 about the bubbles (or balloons) of air in the deep firn of an ice sheet. Like the balloons in my experiment, the pores in those bubbles get smaller and smaller under the increasing weight of ice above as the ice sheet thickens. I thought that Iíd try filling balloons and blocking them with tubes filled with squashed up frost from my freezer (it needs de-frosting but its too full of food at the minute). I scraped off the frost and squashed it as hard as I could into two tubes of plastic water pipe (22mm) then tied the filled balloons open end over the tube. Botjh went down almost straight away so I blew through the tudes and it was easy so what I though was solid packed frost (like that ďfirnĒ he was talking about?) but is wasnít, was it. So the firn mustnít be either until it is squashed even more into a solid lump so those pockets in the firn might be like those balloons do you think?

That diagram that he showed on 27th April got me interested in looking at the links he gave but I couldnít get in to the first two because they want a registration number. How can I get these? I got into the third one with the pictures of ice at http://itia.ntua.gr/hsj/45/hysj_45_03_0357.pdf and theyr wonderful. Look at that fig 9 on page 11. The size of those balloons are tiny but still big when thinking about molecules. How small can those photos get?

Anyway, Iím off to watch the football and will come back tomorrow and see if anybody has any ideas about this.
 

Offline Peter Ridley under another name

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« Reply #6 on: 29/05/2011 18:34:17 »
I have started another of those experiments with balloons, this time filling one from my tyre pump so itís ordinary air not from my mouth because that has CO2 but that balloon didnít go down so it canít be much. I half-filled the other one with CO2 from soda and vinegar then blew it up by mouth to nearly the same size as the air one, with a circumference of 44 v 45 cm. That was as much again so it must have about half CO2 and half air.  Letís see what happens to those ones. Iím guessing that itíll be just the same as the other experiments but Iíll wait and see.

It might be important so I measured the temperature at 18C and the balloon pressure was about 100mb as best I could tell from my tyre gauge. It only moved the thickness of the needle.

CliffordK, you are the only one who has talked about my question and have you done one with argon yet? I got stacks of balloons from Tescoís store in the party section for just £2. I donít know why nobody else is trying to help me here. Have you any ideas? I see that you only made one comment on that question that Pete Ridley asked about ďAnother Hockey StickĒ and didnít follow up on his other comments. Only somebody called Wiybit who changed his name to Jolley- Joliver, and ericwolff were any real help but the thread got locked too soon. I donít know why that happened because Pete Ridley still seemed to have some more questions like I do that is why I have started this question but nobody else is helping and you said it is very interesting. I think it is and my daughter asked at school but they didnít know. I donít know why nobody else wants to help me with this because it puzzles me and them. Iíll tell you tomorrow how the new balloons are doing. The first ones still havenít changed since yesterday.
« Last Edit: 29/05/2011 18:36:37 by Yelder »
 

Offline Peter Ridley under another name

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Why Does CO2 Escape From An Enclosure More Easily Than Air?
« Reply #7 on: 30/05/2011 09:29:51 »
Thereís a funny thing happened in my first balloon that I put CO2 into. When I caught the CO2 n the balloon the vinegar frothed up and some of it went up into the balloon and I couldnít get it out but didnít worry because it stayed in all right. As I told you on the 27th the balloon went down quite a bit in the first two days but stayed at that for the next two days. Now this morning Iíve found a puddle of vinegar outside the balloon but it is still not flat. Its gone down overnight to 85mm. So whatís funny is that a lot of the vinegar got out but the CO2 is still trapped inside. Anybody know why?

Wikipedia told me that vinegar is acetic acid and I found that latex gloves arent much good for strong sulphuric acid but somebody used them and it was OK http://www.sciencemadness.org/talk/viewthread.php?tid=14040 The vinegar I use is malt and it says its 5% acid so is the rest just water?

Why would the vinegar get out and the CO2 stay in? Ive heard about nitrile being better for this but donít know where to get nitrile balloons.
 

Offline RD

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« Reply #8 on: 31/05/2011 04:20:48 »
Possibly the CO2 is reacting with something in the balloon (rather than escaping faster than air) ... http://en.wikipedia.org/wiki/Carbonic_acid

Air is mostly N2 which is unreactive.
« Last Edit: 31/05/2011 04:36:48 by RD »
 

Offline Bored chemist

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« Reply #9 on: 31/05/2011 09:46:48 »
It would be interesting to do this experiment in detail with lots of gases.
There are lots of complicating factors.
One is that the gases don't need to find holes through the latex to escape, they can "dissolve" in the rubber, diffuse through it, and escape.
Secondly the air outside a balloon full of CO2 will diffuse into the balloon (which is rather counter-intuitive) so the balloon is filling up as well as emptying.
Once you have taken those effects into account, if there's still anything "odd" to explain then we might need to look at the different measurements of diameters.
 

Offline Peter Ridley under another name

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« Reply #10 on: 31/05/2011 10:21:16 »
Hello RD did you find something about the CO2 going into the balloon instead of going through it or is it just a guess. The latest on my leaky balloon is that it went down to smaller than a tennis ball and started to bulge at the side. I found a pin-hole where vinegar could get out if I squeezed it so I ditched that experiment. The new one I started two days ago there is no difference in the size of either balloon, one has only air and the other about half air and half CO2. If the CO2 was going into the balloon like you said then the one with half CO2 should have gone down a bit by now.

Iím very puzzled by that because I know that condoms are made from latex like the balloons and they have pores. I did a google of porosity and latex contraceptives and the first one at http://www.ecp-help.org/1652/condom-use-for-herpes.html says that
Quote
In their function as a contraceptive, condoms would have to be impermeable to spermatozoa, which are approximately 3000 nm in size. HSV-2 is considerably smaller than spermatozoa, at about 160 nm, and HIV is smaller still at 125 nm. Electron microscopy of male condoms shows an absence of full-thickness pores, but occasional pits secondary to imperfections in manufacturing. Permeability depends not just on the size of any pores in the latex barrier, but also variables such as the shape of the infectious agent, surface tension, temperature, pressure and pH of the environment

The size of those sperm and herpes is much bigger than the size that Pete Ridley said the gas molecules are http://www.thenakedscientists.com/forum/index.php?topic=38675.0 Those sperms and herpes are 160nm and 125nm but Pete Ridley said that the air molecules are all a lot smaller and less than 1nm so if condoms let the herpes through why can they hold in the air never mind the CO2. Any ideas anybody?

OK it says that the pores donít go right through and it also says about the shape temperature  pressure and pH so itís a very complex thing even just in a balloon never mind deep down in the ice. Even Professor Wolff said that
Quote
I think that none of us has a definite molecular-level understanding of the physical process occurring at closeoff, and it would be great if someone can do the experiments in the lab to understand that better.  But it won't alter the empirical facts
http://www.thenakedscientists.com/forum/index.php?topic=38675.75 

Iím still puzzled about why the vinegar leaked out but not much CO2 at first. Anybody any ideas?
 

Offline Bored chemist

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« Reply #11 on: 31/05/2011 13:13:32 »
"so if condoms let the herpes through why can they hold in the air never mind the CO2. Any ideas anybody?"
Who says they do let herpes through ?

(apart from the Catholic church who are clearly only concerned about "truth" as it was written down about 1700 years ago)

"Iím still puzzled about why the vinegar leaked out "
"I found a pin-hole where vinegar could get out"
 

Offline Peter Ridley under another name

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« Reply #12 on: 31/05/2011 16:46:32 »
Bored chemist you said some funny things that havenít helped me. If the gases don't need to find holes through the latex to escape but can dissolve in the rubber, diffuse through it, and escape why did the balloon with air in it not dissolve those gases and go down?  As for the air outside a balloon full of CO2 diffusing into the balloon and filling it, I thought that there is something called partial pressure that makes them try to go equal so if there is only 0.04% CO2 outside and 100% inside why would any go inside from outside? That needs explaining I think. And I donít know more than one way of measuring a balloons diameter, thatís with a tape measure so please how else can I do it?

Thanks for asking about who said herpes got through the condom. I did another check and according to this one http://www.ncbi.nlm.nih.gov/pubmed/1411838
Quote
A suspension of polystyrene 110 nm microspheres labeled with fluorescent dye served as the HIV-sized particle model in semen. They challenged each condom with this suspension for 30 minutes. The test did not include motion since stretching over the penis accounts for most pore stretching. Leakage of fluorescent dye occurred in 29 condoms (p .03). 21 condoms leaked at minimum leak rates 1 nl/s, 7 at 1-6 nl/s, and 1 at around 10 nl/s
HIV looks a bit smaller than herpes but still similar size. I might be wrong about herpes but maybe not about HIV but what is more important is how big are the pores in latex, especially the balloons Iím using. There is another site http://www.straightdope.com/columns/read/1178/can-hiv-pass-through-the-pores-in-latex-condoms that says the size of the pores in latex gloves is about 5 microns but condoms are better but no size is given. Another site says that
Quote
industry officials admit condoms have holes 50 to 500 times the size of the HIV virus
http://www.dianedew.com/condom.htm and that is about 5-50microns. Does anybody here know anything about the size of pores in latex balloons or condoms because the Internet gives different answers.

You also put two bits of what I said together like I said them at the same time but I didnít. Isnt that called cherry picking? and it sounded a bit sarcastic. I said yesterday that
Quote
Iíve found a puddle of vinegar outside the balloon but it is still not flat(thatís the balloons I meant not the vinegar or CO2). Its gone down overnight to 85mm. So whatís funny is that a lot of the vinegar got out but a lot of CO2 was still trapped inside
Today I said that
Quote
Iím still puzzled about why the vinegar leaked out but not much CO2 at first
You havenít explained why the vinegar got out yesterday but the balloon still had a lot of CO2 in it. Anybody know why?Ē Iíd expect the gas to get out easier than the liquid.
 

Offline CliffordK

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« Reply #13 on: 31/05/2011 21:53:24 »
Partial Pressures may not be a major influence on rubber balloons as the rubber itself will exert pressure on the gas inside the balloon. 

The Partial Pressures might, however, be an influence on Mylar balloons which may have the same pressure inside and outside.
 

Offline Bored chemist

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« Reply #14 on: 31/05/2011 22:19:06 »
The difference in partial pressure of CO2 inside and outside a CO2 filled balloon is about 1 atmosphere.
The difference in partial pressure of nitrogen between the inside and outside of a CO2 filled balloon is about 0.8 atmospheres and the partial pressure difference for oxygen is about 0.2 atmospheres. The difference in pressure due to the elasticity of the balloon is rather small; certainly less than 10%.

Some materials just dissolve netter than others.
CO2 may be more or less soluble in rubber that O2 or N2. I don't know.

It seems not all condoms are created equal. The ones I have seen are tested by seeing if they conduct electricity (Ouch!).
That rules out much of a leak.
Also, as you say, you can blow them up, so we know they don't leak.

Until the vinegar leaked out, it was in the way of the CO2. Also there's the fact that the liquid would dissolve CO2 and act as a reservoir.

Measuring the diameter of the balloon isn't the whole story; you need to know what's in it, and that's not always the same stuff that you start with.
 

Offline Peter Ridley under another name

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« Reply #15 on: 31/05/2011 23:26:08 »
Clifford if the balloon is exerting a pressure wonít that reduce the volume that the CO2 would otherwise reach if the balloon isnít holding it in? Doesnt that keep the CO2 partial pressure higher? You say may and might a lot so are you just guessing.

Bored chemist if the partial pressure of CO2 in the balloon that only has CO2 in it is nearly 1 atmosphere (couldnít it be a bit more because when I measured the filled balloon pressure it was about 100mb or a bit less) and the partial pressure outside the balloon is almost nothing how would CO2 be going into the balloon from outside like you said before? Surely the flow would be from inside to out until both are equal.

Are you saying that the CO2 dissolves into the latex instead of going through it and if you are do you know this or are you just guessing.

I found a site that talks about tyres filled with CO2 going down faster than those filled with air http://www.bikeforums.net/archive/index.php/t-154847.html and somebody called supcom said heíd done an experiment and said
Quote
I am confidant in concluding that CO2 leaks out of a typical bicycle tire more rapidly than air
Another one called Al1943 said he had found the same happened to him. Have you done any experiments on this or not or are you just guessing at what might happen like Clifford might be.

You said I said you can blow a contraceptive up but I didnít say that but I did when I was little then somebody told me that it wasnít a balloon and I got into trouble for having it.

About the vinegar I think the answer is that the vinegar ate a hole at the bottom and leaked out and stopped the CO2 getting out until I measured the balloon and put it back down with the hole out of the vinegar then the CO2 could get out. If the CO2 dissolved in the vinegar the balloon would have gone down faster. You said that
Quote
the liquid would dissolve CO2 and act as a reservoir
but does CO2 dissolve in vinegar and how much? After all it was the vinegar that released the CO2 in the first place so why would it go back in?

You said
Quote
Measuring the diameter of the balloon isn't the whole story; you need to know what's in it, and that's not always the same stuff that you start with
but why would anything go into the balloon from outside. I filled one with CO2 and one with air and how would something else get into either balloon while they were still blown up with those things. Wouldnít that make them get bigger? What makes you think that something else got in.
 

Offline Bored chemist

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« Reply #16 on: 01/06/2011 07:05:13 »
A long time ago (maybe 30 years or more) there was a TV show called "Young scientist of the year".
School kids did science projects as a competition.
One of the things they investigated was this "odd" effect where CO2 leaks out of balloons more quickly than air, even though  it's heavier.

I think we can all agree that the effect is real.

The explanation is another matter.
"but does CO2 dissolve in vinegar and how much?"
Yes, but I don't know- probably about as   much as dissolves in water.

"but why would anything go into the balloon from outside. "
As I have said twice now, diffusion works both ways.
The air outside a balloon full of CO2 diffuses in.



 

Offline RD

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« Reply #17 on: 01/06/2011 08:20:58 »
To investigate if the CO2 was reacting with the latex Ö
Obtain two glass carboy type jars
Put a few latex balloons in one jar (not inflated).
Fill both jars with CO2
Seal the jars with manometer airlock type device.

If the CO2 is reacting with the latex the water in that manometer will be drawn into the jar.

Note variations in temperature will change both the manometer levels,
but this can be cancelled out by your control jar (with CO2 but no latex balloons).

[Jars must be kept together so are at the same temperature]
« Last Edit: 01/06/2011 08:35:11 by RD »
 

Offline Peter Ridley under another name

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Why Does CO2 Escape From An Enclosure More Easily Than Air?
« Reply #18 on: 01/06/2011 13:48:06 »
RD did you try that experiment yourself or just read it somewhere. I couldnít find anything about it on the Internet.

I think one of the reasons it wouldnt post first time was that Id put url= instead of utl] but why didn't it tell me what was wrong.
« Last Edit: 01/06/2011 13:59:13 by Yelder »
 

Offline rosy

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Why Does CO2 Escape From An Enclosure More Easily Than Air?
« Reply #19 on: 01/06/2011 13:48:39 »
That typically means you've inadvertantly used a word on the blacklist... the forum blacklist is more-or-less copied from the wikipedia blacklist (mostly words used commonly in spam posts, so often clothes, drug, or jewellery brand names), but the moderators can add other words associated with spam, or put words we would like to allow people to use to the whitelist.

Unfortunately it's not a terribly sophisticated system, and even using words that contain words on the blacklist will also prevent you from posting.

You'll just have to work out what the word it won't let you post and then either work round it or ask us to add it to the whitelist (obviously you'd need to put in extra c-h-a-r-a-c-t-e-r-s).
 

Offline Peter Ridley under another name

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Why Does CO2 Escape From An Enclosure More Easily Than Air?
« Reply #20 on: 01/06/2011 13:51:22 »
Rosy thanks fr that help. Ive tried lots of things and nothing worked so will have to do as you said and look for nasty words.
 

Offline Peter Ridley under another name

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Why Does CO2 Escape From An Enclosure More Easily Than Air?
« Reply #21 on: 01/06/2011 13:55:44 »
Bored chemist I couldnít find anything about latex dissolving CO2 and mostly its the other way round so are you right about that or just guessing. One site says that the formula for pure latex is C3H3N so as youíre a chemist does that tell you anything about CO2 dissolving in it.

 

Offline Peter Ridley under another name

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« Reply #22 on: 01/06/2011 13:56:27 »
A lot of people say on the Internet about their tyres going down when they fill them with CO2 but not with air. Most of them I found are talking about bike tyres like the one I said yesterday http://www.bikeforums.net/archive/index.php/t-154847.html so I did another google and found this http://velonews.competitor.com/2009/02/bikes-and-tech/technical-qa-with-lennard-zinn-large-molecules-and-short-frames_87175. It looks like Glenn who asked the question made the same mistake about the size of CO2 as what Pete Ridley was saying on 14th April about
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the paleoclimatologists and their models .. What they do not seem to consider is that it is the kinetic not collision diameter that is appropriate at this stage
http://www.thenakedscientists.com/forum/index.php?topic=38675.0.

Leonard and the
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atmospheric chemist/bike nut Alan Hills
on that bike site seem to know about this CO2 leak happening and Alan Hills said
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Permeation by diffusion predicts gas leakage rates proportional to the inverse of the square root of their molecular weights. Using air as a reference the predicted leakage rates for common gases are: helium 2.7, air 1.0, nitrogen 1.02, oxygen 0.95, argon 0.85, carbon dioxide 0.81. It turns out however that the leakage rate of CO2 is huge, and the reason is that it is actually soluble in butyl rubber and is thus not constrained to normal permeation loss, it can transfer straight through the bulk rubber resulting in severe tire pressure loss on the order of a single day. .. A reference dealing with CO2 transfer through latex rubber sheds light on the loss process.
That reference he gave is to http://www.madsci.org/posts/archives/may98/895552329.Ch.r.html by Dr. John Christie of La Trobe University in Australia who is
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a theoretical chemist, with a particular interest in the development and application of simplistic model theories for chemical problems. My main area of interest is reaction kinetics, mechanism, and energy transfer in reactions.
http://www.latrobe.edu.au/chemistry/people/christie.html.

Dr. Christie sounds as though he is an expert in this so Iíll try to get him to help and let you know what he said or maybe heíll talk here. Iíll ask him if heíll help here.
 

Offline Peter Ridley under another name

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« Reply #23 on: 01/06/2011 13:57:08 »
Rosy that problem seems to be c h a c h a
 

Offline Peter Ridley under another name

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« Reply #24 on: 01/06/2011 22:28:22 »
Iíve E-mailed Dr. Christie and hope that heíll get back to me but meanwhile I had a good read of what he said about CO2 in bike tyres at http://www.madsci.org/posts/archives/may98/895552329.Ch.r.html. Heís an expert and said
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The answer is that the carbon dioxide is much more "soluble" in the rubber that the balloons are made out of. For helium and oxygen, the chains of molecules in the balloon rubber repel the gas molecules, and they have to thread a maze, at best, to escape the balloon
Why did he put the word soluble in those commas as though it wasnít quite right. Is it dissolving really like things dissolve into water or just going into tiny holes in the balloon and thatís not really dissolving is it?

Then he says about the CO2 having to
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thread a maze, at best, to escape the balloon
so that must mean it might be worse than a maize. If you look at those pictures that Pete Ridley talked about on the ďAnother Hockey Stick Illusion?Ē thread http://www.thenakedscientists.com/forum/index.php?topic=38675.50 on 27th April at 22:39 in Figure 11 at http://itia.ntua.gr/hsj/45/hysj_45_03_0357.pdf on page 369 especially at the top of the bottom picture it looks like a honeycomb kind of maize for air to get through. Isnt what Dr. Christie says something like what Pete Ridley says is in the ice?

He also said
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carbon dioxide is attracted to the chains of rubber molecules, and drawn in between them until it permeates the whole of the rubber. The rubber actually swells in the process. Once that has happened gas molecules can just as easily escape from either side of the balloon, and so the gas is lost relatively fast.
What attracts it to the rubber? And can the same thing happen in the ice that Pete Ridley talks about? As well does the rubber have to swell before the gas escapes? Why canít gas just keep on going through that maize on the way out to the open air? Wonít the pressure inside the balloon push the gas out instead of letting gas in from the outside.

Any ideas anyone?

I did do a google about Dr. Christie and came across a video ďGlobal Warming: A Scientific and Biblical Expose of Climate ChangeĒ http://www.answersingenesis.org/media/video/ondemand/global-warming/global-warming but it was the wrong Dr. Christie. It still has some interesting stuff about climate change especially a graph at 23:30 minutes by a weather man called Mike Oard which shows how temperature change is caused by sunspots not CO2. I might start another question on that one.

Are people here just guessing at what is happening with the CO2, just like Professor Wolff said to Pete Ridley on http://www.thenakedscientists.com/forum/index.php?topic=38675.75   
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I think that none of us has a definite molecular-level understanding of the physical process occurring at closeoff, and it would be great if someone can do the experiments in the lab to understand that better
. Thatís OK about balloons and contraceptives but not about air and CO2 in bubbles in ice.


I hope that Dr. Christie can be bothered to say something here like I asked him if he would.
 

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Why Does CO2 Escape From An Enclosure More Easily Than Air?
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