Sciencemadness Discussion Board - What's the densest gas (or mix) you can create?

What's the densest gas (or mix) you can create?

woelen - 3-3-2013 at 13:15

I intend to do a nice experiment in which an aluminium boat is floating on a dense gas. I have seen the YouTube film with a boat floating on SF6. This is quite impressive, but not something easily done at home. SF6 is not a cheap and easy to obtain chemical.

SF6 is quite dense, its molecular weight is 146 gram/mole. Its density is appr. 5 times the density of air.

I also have considered volatile liquid compounds with high molecular weight, but these do not allow 100% pure gases without condensation. So, the compound really must be a gas at let's say 20 C.

Some fairly dense alternatives, which can be made cheaply (e.g. a few liters of gas can be made for 1 euro or so):

Cl2 : 2.5 times the density of air.
C4H10: 2 times the density of air.

A somewhat more expensive alternative, but very easy to prepare is ONBr, which is almost 4 times as dense as air and can be made very easily by adding solid NaNO2 to 40% HBr. This leads to formation of a nearly black liquid (aqueous solution of ONBr) and ONBr bubbles from this liquid (ONBr does not dissolve in water that well). Food grade NaNO2 is dirt cheap for me, but unfortunately, HBr is quite expensive. I made some myself from NaBr and half-concentrated H2SO4 and distilled this, but for a few liters of gas you need quite a lot of HBr. Another disadvantage of ONBr is its very dark color. The gas is deep brown/red, much darker than Br2 and even darker than NO2. The gas also is quite toxic.

I already did experiments with this gas and it is amazing to see how it can be poured, almost like a liquid. It very slowly diffuses with air.

Are there any gases which have even better properties and are affordable (ONBr is at the border for me, the experiment would cost at least a few euros)? So, gases, based on iodine or other expensive heavy elements are not interesting. Such gases I will not make in liter quantities. The gases also must be achievable for a home chemist without special expensive equipment and the gas must be air-stable. Toxicity like Cl2 or NO2 is not a real problem, as long as it is not insanely toxic like some chemical warfare gases.

[Edited on 3-3-13 by woelen]

neptunium - 3-3-2013 at 13:41

what about freons? some chloro fluoro alcane are non toxic, non flamable, dirt cheap, can be purchased by the gallon, and quite dense!

Metacelsus - 3-3-2013 at 15:14

Uranium hexafluoride is the densest known gas (in its gaseous phase, which is above 57 C at 1 atm). Tungsten hexafluoride is the densest known gas at STP (11x denser than air). However, you probably won't be able to make any of these, unless you can work with fluorine.

neptunium - 3-3-2013 at 17:50

Quote: Originally posted by Cheddite Cheese

Uranium hexafluoride is the densest known gas (in its gaseous phase, which is above 57 C at 1 atm). Tungsten hexafluoride is the densest known gas at STP (11x denser than air). However, you probably won't be able to make any of these, unless you can work with fluorine.

he mentioned cheap and readily availlable .

kristofvagyok - 3-3-2013 at 18:01

That idea with UF6 smiled me. Would be interesting to work with a gas like that(:

What about chloroethane? It is bit more dense than air, but it could be easily made, could be handled safe and it's cheap. Or freons... On ebay a lot freon containing fire exhauster could be found, sometimes for dirt cheap.

phlogiston - 4-3-2013 at 03:02

xenon MW = 131 (d = 5.89)
krypton MW = 83.3 (d=3.75)

methylbromide, MW = 94.94 gram/mole
On a very hot summer day (bp=42 deg C) methyliodide would ofcourse be even denser (MW= 141.09), but given the all-time highest temperature in the Netherlands was 38.6 deg C in Warnsveld (1947), this will only work in the hot attic of your house, not outside, and I'm not sure you want to do that with such toxic gasses

MrHomeScientist - 4-3-2013 at 07:05

I was going to suggest xenon as well. If I remember right, it is used occasionally in welding.

I am fortunate in that I actually get to work with SF6. You're right, it is not cheap and is only sold by the big chemical suppliers. I do an educational outreach science stage show for kids, and breathe this as one of my demos. It's really incredible how low your voice gets, and pretty shocking to the audience every time. I love this demo because everybody knows about helium, but very few have heard of SF6 so it's always very surprising (and hilarious).
I've also floated balloons of regular air in a beaker full of the gas. It works great, and is very eerie. I always wanted to scale it up to a fish tank, but that would be some serious cash!

Edit: Xenon is also safe to breathe, so if you get your hands on some you should definitely try that out

"Safe" being relative of course, these gases are simple asphyxiants.

[Edited on 3-4-2013 by MrHomeScientist]

woelen - 4-3-2013 at 10:48

Xenon also is very expensive. Its price is expressed in euros per gram! Not something affordable for this kind of experiments.

Suitable freons have densities in the order of 2 to 3 times the density of air. I am afraid that the densest fairly affordable gas for me indeed is ONBr. Making 2 liters and floating a balloon in the gas should be possible.

Fantasma4500 - 4-3-2013 at 11:00

in my country argon is considered directly toxic, still shaking my head over this statement....
sounds really incredible.. need to go watch this experiment.. my bet would be some long very complicated gasses, but how long chemical formulas can they get when youre thinking relatively OTC.. that might be the problem..

Pok - 4-3-2013 at 11:23

HI is 4.5 times as dense as air. And iodides aren't soo expensive. If the whole iodine is converted to HI you will need about 35 grams KI for 5 Liters HI.

Here you can see many gases with their densities (you can sort them by density ("Dichte")):
http://de.wikibooks.org/wiki/Tabellensammlung_Chemie/_Dichte...

Almost all high density gases are either instable (e.g. TeH2) or impossible to make at home (halocarbons). But I didn't know that something like ONBr exists. So maybe there are some other strange alternatives beside that.

If you only want to let a balloon flow then even CO2 should be sufficient.

[Edited on 4-3-2013 by Pok]

MrHomeScientist - 4-3-2013 at 13:01

I forgot about CO2 - I've also floated soap bubbles on that gas before. Simply place dry ice in a bowl, let sit for a few minutes to fill with gas, and gently blow bubbles over top of it so that they fall down into the bowl. I tried it with a tiny balloon of air, but that was too heavy.

I think if you made ONBr, the preparation and appearance of the gas would be just as interesting as floating things in it!

Adas - 4-3-2013 at 13:28

Quote: Originally posted by woelen

Xenon also is very expensive. Its price is expressed in euros per gram! Not something affordable for this kind of experiments.

Suitable freons have densities in the order of 2 to 3 times the density of air. I am afraid that the densest fairly affordable gas for me indeed is ONBr. Making 2 liters and floating a balloon in the gas should be possible.

I think it would not be possible becuase the ONBr would react rapidly with the balloon.

woelen - 4-3-2013 at 13:28

Interesting list of gases. All those fluorine-containing gases have amazing density, e.g. something like C4F10 or TeF6. Nice stuff, but as you already said, not something you can make at home. I think that the densest gas which I can make at home and which is air stable and cheap is ONBr. HI is not a real good alternative. It fumes in contact with air and very quickly becomes a nasty acidic wet mess. ONBr is stable in contact with air and does not fume. It has the same smell as ONCl, somewhat 'spicey', quite different from Cl2 or Br2.

I made a little movie of pouring ONBr from an erlenmeyer. It nicely shows the density of the gas and how well it remains separated from air (watch the content of the erlenmeyer).

http://www.homescience.net/chem/ONBr.avi

Beware, it is a big file (almost 40 MByte), it must be processed and compressed before it will be available on my website (lateron I will replace the link by another better suited file). I already post it here, so that you can see how the gas behaves. The black liquid in the erlenmeyer is not Br2, but appr. 40% HBr, to which some solid NaNO2 is added. The black color is due to the ONBr, dissolved in this liquid.

[Edited on 4-3-13 by woelen]

bhattshivamm - 4-3-2013 at 23:43

As i had read before some time, methylene iodide (diiodo methane - CH₂I₂ is the densest liquid known (except mercury)... so i assume its vapors might also be so much dense... (just assuming)

Glucose Oxidase - 5-3-2013 at 06:30

I think i must warn you that if you want to use argon or xenon they might contain some radon impurities which causes infertility (common among argon welders) so use it with some protection ............ best wishes

neptunium - 5-3-2013 at 08:30

the amount of radon in xenon and argon is so small t and its radioactive half life so short (about 4 days) that you would have to inhal so much that the lack of oxygen will kill you long before any radiation sickness symptoms....its like saying bananas contain the dangerous isotope K40! you`ll be fine

watson.fawkes - 5-3-2013 at 09:37

Quote: Originally posted by Glucose Oxidase

[...] if you want to use argon or xenon they might contain some radon impurities which causes infertility (common among argon welders)

Got a citation for that? Seems mighty unlikely. There are plenty of ordinary chemical hazards in welding; you'll have to supply a citation that links to radon specifically.

Radon has a half-life of 3.8 days and its daughter isotopes have half-lives in minutes. If you put some radon in a tank, it's almost all gone within a couple of months. Because there's no uranium-bearing rock formation in the tank to replenish the radon, it simply goes away.

phlogiston - 5-3-2013 at 12:51

While reduced fertility has indeed been found repeatedly among welders, it is more commonly believed to be linked to inhalation of metal fumes.

AndersHoveland - 5-3-2013 at 22:52

I am sure there are denser gases, but they are likely very poisonous. S2F10, for example, boils at 30.1 °C (around the temperature outside on a warm day). It would be 9 times heavier than air.

Xenon gas is 90% as dense as SF6. Xenon has mild anesthetic qualities due to its physical properties, like several other well known anesthetic compounds (nitrous oxide and chloroform vapors, for example). (the physical effects are probably are due to high solubility in lipids)

If you have ever seen a balloon filled with xenon being dropped, it is conspicuosuly heavy for a gas.
http://www.youtube.com/watch?v=QLrofyj6a2s

[Edited on 6-3-2013 by AndersHoveland]

Glucose Oxidase - 8-3-2013 at 11:12

Quote:

actually i have no citation . My father , a urologist, told me so but i never researched it on the internet or in any book

Protection is better than cure so i just want woelen to be careful

[Edited on 8-3-2013 by Glucose Oxidase]

garage chemist - 8-3-2013 at 11:30

The perfluorocarbons are low-boiling and have an extremely high vapor density. Simply heat perfluorohexane (C6F14) to a boil and you have a gas phase with a molar mass of 338g, around 14g per liter.
Otherwise, try boiling some carbon tetrachloride and try to float your aluminum foil boat on these vapors.

DraconicAcid - 8-3-2013 at 11:40

Quote: Originally posted by garage chemist

Otherwise, try boiling some carbon tetrachloride and try to float your aluminum foil boat on these vapors.

If the vapour is hotter than the room, it won't sit nicely in the tank, but will mix due to convection currents.

AndersHoveland - 9-3-2013 at 02:43

Perfluoropentane boils at 30 °C (warm day), and the vapors are about 10 times denser than air.

Quote: Originally posted by garage chemist

The perfluorocarbons are low-boiling and have an extremely high vapor density. Simply heat perfluorohexane (C6F14) to a boil and you have a gas phase with a molar mass of 338g, around 14g per liter.

Or put the entire demonstration inside an enclosed transparent container, with a little hole. Then add helium and heat the inside of the container to 56 °C. Then preheat the fluorohexane and introduce it into the container. Then finally, introduce the aluminum foil boat through an opening in the middle. 56 °C air feels like the inside of an oven. Might use an insulated mitten or a pincher stick to introduce the boat.

[Edited on 9-3-2013 by AndersHoveland]

franklyn - 9-3-2013 at 07:07

www.youtube.com/watch?v=hbIXWe9IZgo
I think obtaining funding source is the problem.
SF6 is hard to beat for utility and safety.
www.youtube.com/watch?v=XjCmwuGKR6g

The entire list of gasses lighter than air fits on one line :
H2 , He , Ne , CH4 , NH3 , HF , B2H6 , C2H2 , C2H4 , HCN , N2 , and CO.
All the other gasses are heavier than air. Argon, CO2 , ethane (C2H6)
propane (C3H8) , butane (C4H10) , all the Freons ( CF4 , C2F6 , C2F4H2
CF2Cl2 ) and others.
The density of a gas is proportional to the sum of the atomic weights in
one molecule. Individual atoms: C=12, N=14, O=16 gm/mole.
So molecules: N2=28 and O2=32 , and so air ( 80% N2 + 20% O2 )
averages abut 29 gm/mole.
CO2 = 12+16+16 = 44 , definitely heavier than air. All these gasses have
the same number of molecules in a given volume, but the molecules weigh
different amounts. So a heavy molecular weight makes a heavy gas.
- Jim Swenson
From here _
www.newton.dep.anl.gov/askasci/chem03/chem03251.htm

www.wisc-online.com/objects/ViewObject.aspx?ID=GCH5704
http://yeroc.us/calculators/gas-density.php

www.engineeringtoolbox.com/specific-gravities-gases-d_334.ht...
www.engineeringtoolbox.com/gas-density-d_158.html

Organics such as Xylene have reasonable density
Boiling point (760 torr): 135 to 145 ºC
Vapor density (air = 1 at boiling point of xylene): 3.7

Ignition of the combustible vapor is a consideration.
Flash point: 27 to 32 ºC (81 to 90 ºF).
Autoignition temperature: 464 ºC (867 ºF).
Flammable limits in air (percent by volume): Lower, 1 ; upper, 7.
From here _
www.osha.gov/SLTC/healthguidelines/xylene/recognition.html

www.engineeringtoolbox.com/explosive-concentration-limits-d_...

______________________________________________

Ozone depleteing Freons are an alternative
http://en.wikipedia.org/wiki/R-114
http://en.wikipedia.org/wiki/R-123

Halocarbons generally are quite dense
http://en.wikipedia.org/wiki/List_of_refrigerants

One having a boiling point around room temperature should work.

.

kristofvagyok - 10-3-2013 at 10:40

This is also not the cheapest reaction but it's really easy to make. Trifluoroacetonitrile could be easily made via mixing P2O5 with trifluoroacetamide and dry distill it. A dense gas (95g/mol) will come over what could be easily condensed with liquid nitrogen to a white solid if needed.

Trifluoroacetamide could be easily made from TFA and ammonia, and I think P2O5 is also not an impossible thing to get.

franklyn - 10-3-2013 at 12:17

As DraconicAcid observes above ,
Regardless how dense a vapor, if it needs to be much hotter
than ambient air temperature the boundary will be turbulent.
Why a refrigerant gas that boils at subzero temperature is
preferable. Something that is not too far from ambient temp.
might do, such as this _

1,1,2-Trichloroethylene
Boiling point: 86.7 °C
Vapour density: 4.53 (air =1)
From here _
www.environment.gov.au/atmosphere/airquality/publications/so...

It is being phased out of commerce and is increasingly hard to find as a technical
grade retail product. Try looking first at your local auto parts store for degreasers.

Another prospect and easy to make with Acetone and hypochlorite

Chloroform
Boiling point: 62 °C
Vapour density: 4.1 (air =1)
From here _
www.osha.gov/SLTC/healthguidelines/chloroform/recognition.ht...

An electronic circuit board flux remover might serve the purpose

1-bromopropane
Boiling point: 71 0°C
Vapour density: 4.3 (air =1)
From here _
www.cdc.gov/niosh/ipcsneng/neng1332.html

Other candidates
www.techspray.com/product-info.php?pId=31&cId=9
www.techspray.com/download-msds-document.php?pId=31&mId=...

www.techspray.com/product-info.php?pId=18&cId=9
www.techspray.com/download-msds-document.php?pId=18&mId=...

"Radio Shack" Rosin Flux Stripper
http://hpd.nlm.nih.gov/cgi-bin/household/brands?tbl=brands&a...

_________________________________

The compound kristofvagyok entertains
Vapour density: 3.3 (air =1)
has the right boiling point - 64 0°C

www.lookchem.com/Trifluoroacetonitrile
www.chemicalbook.com/ProductMSDSDetailCB5321126_EN.htm
MSDS link top of page here _
www.sigmaaldrich.com/catalog/product/aldrich/544078

.

watson.fawkes - 10-3-2013 at 13:56

Quote: Originally posted by DraconicAcid

If the vapour is hotter than the room, it won't sit nicely in the tank, but will mix due to convection currents.

Not necessarily. Convection currents arise proximately due to differences in density. Temperature differences causes convection currents in air (and other gases) because temperature differences cause density differences. With dissimilar gases, though, a denser gas will tend to settle out underneath a less dense one, regardless of temperature. This separation is not a two-phase system, not exactly, because the boundary is not a strict layer; there's some mixing. Nevertheless, if the molecular weight difference is high enough, the boundary region can be fairly narrow.

As to woelen's original question, I don't know that there's much that's inexpensive that satisfies all the other criteria. One class of substances, however, that are readily available, though not terribly inexpensive, are the perfluorinated polyethers that are used for vapor phase soldering, and at even higher molecular weights, for vacuum pump oils. Look up the Galden HT line. They need to be heated to vaporize, but it means you could make your demonstration boat change height in a tall tube depending on the relationship of heat vs. cooling.