What gas is heavier than air?

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?

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.

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.

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.)

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.



Is there a known planet where a balloon filled with air from planet Earth would float?

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!

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.

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.

Venus. Its atmosphere is almost entirely CO[sub]2[/sub].

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 450º C.

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.

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.

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

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:


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.

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

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.

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!

Sulfur Hexafluoride

:dubious: 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.