I tried to extract hydrogen for my kid's birthday, by mixing caustic soda with water and aluminum foil (mixed in a glass bottle). A lot of heat and (hopefully)hydrogen was released.

However, within 2-3 hours, the balloons started losing altitude and began falling down. I supposed it was caused by losing the gas slowly.

But when I tried to burn the ballon the next day it did not create the pop sound for the hydrogen test.

Please excuse me if this is a naive question. I'm curious since this is the first time I'm dealing with hydrogen and balloons. I attempted this for almost 4-5 time. And every time the balloon stopped flying within 2-3 hours. All other balloons filled with air did not lose gas.

I want to know what happens to the gas. Does it go out? Is it some sort of diffusion?


  • $\begingroup$ Friend first of all things using hydrogen is very dangerous and especially in ballons. Be precautious. I have already met with an Hydrogen accident like this one done (faultof the party organizer) $\endgroup$ – user99515 Dec 24 '20 at 3:03
  • $\begingroup$ Thanks, I will be, It was outdoor and from where I am, Helium is not easy. $\endgroup$ – Mat Dec 24 '20 at 3:09
  • $\begingroup$ Thanks, It's weird why air ballons did not deflate while Hydrogen ones deflated fast. Also if I understand correctly H2 is inflammable highly, When I ignited the balloon the next day, There was no loud pop sound, just a regular balloon pop sound. $\endgroup$ – Mat Dec 24 '20 at 3:25
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    $\begingroup$ He ballons you can buy on fairs ec. are usually made from some metallised plastic instead of rubber, which makes them keep the He longer. H2 is similarly good in diffusing through thin, biaxially stretched rubber. $\endgroup$ – Karl Dec 24 '20 at 9:51
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    $\begingroup$ Hydrogen diffuses through rubber faster than anything else. Helium is also fast which is why most commercial helium balloons are not made of rubber but other less-permeable plastics which are also usually metallised to further reduce diffusion. $\endgroup$ – matt_black Dec 24 '20 at 9:52

Hydrogen, having very small and fast moving molecules, diffuses faster and through smaller holes than air. Your balloons seem to be permeable for hydrogen. Try a different brand, if it helps. But as others have mentioned, rubber is not the best material to keep hydrogen. Better is a metallised plastic.

Pure hydrogen just burns in a flame. If you have ever watched the film footage (1937) of the catastrophic accident of the airship Hindenburg , it was just a huge scale of burning in a flame.

What makes an explosive "bang"is a hydrogen mixture with air, even better with oxygen. Because hydrogen does not explode, until is contains >6% v/v of oxygen.

Any binary chemical explosion of gases requires a self-sustaining chain reaction. That does not happen if a mixture contains too little of one of mutually reacting gases.

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    $\begingroup$ Agree with the first part, which is the answer. About the second part, if you mean that pure hydrogen doesn't burn and so it does not pop, fine. But otherwise of course it pops. I won't compare Hindenburg whit a bottle. Why the Hinderburg did not exploded was likely its pressure and size being big enough, or trapped gas sacks popping in sequence. Nor the balloon of OP contained pure hydrogen. $\endgroup$ – Alchimista Dec 24 '20 at 9:35
  • $\begingroup$ @Alchimista How do you interpret "It just burns." ? It was not clear or I have missed it that it did not contain pure/nearly pure hydrogen. Hydrogen does not explode, until is contains >6% v/v of oxygen. $\endgroup$ – Poutnik Dec 24 '20 at 9:44
  • $\begingroup$ I have missed the just burned part. I wasn't discussing the "intensity of the stuff". I simply understood that hydrogen wasn't enough to observe its burning, or perhaps the balloon was much opened for the test. Anyway these are details which are difficult to quantify here. $\endgroup$ – Alchimista Dec 24 '20 at 9:44
  • $\begingroup$ A curiosity about diffusion. Working with a vacuum/argon line, we observed some vacuum forming overnight if the system wasn't operated. It was due part of the piping .... The material let some of the argon flow out. I wonder how much vacuum one can get using just selective membrane... $\endgroup$ – Alchimista Dec 24 '20 at 9:52
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    $\begingroup$ @Alchimista The passing gas will diffuse until its partial pressures are equal. If there is 1 L of passing gas at 1 ATM, connected via a semipermeable membrane to 100 L of not passing gas at 1 ATM, the residual pressure at the 1 L side would by approx 0.01 atm $\endgroup$ – Poutnik Dec 24 '20 at 10:23

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