# I'm trying to decide on a gas which will be good to use to fill a balloon and keep a weight afloat on the surface of a body of water. The only issue is that it has to be a gas produced from a...

I'm trying to decide on a gas which will be good to use to fill a balloon and keep a weight afloat on the surface of a body of water. The only issue is that it has to be a gas produced from a chemical reaction which means that Helium cannot be used. so far Nitrogen looks the most promising because it is light, if anyone can think of another gas that could achieve the objective it would be really helpful.

I only need the names of some gases that could be used, I can figure out how to make them and how much I will need to make on my own.

t-nez | High School Teacher | (Level 3) Associate Educator

Posted on

Hydrogen is a lighter-than-air gas that can be produced by chemical reactions. The next lightest option would be hydrogen fluoride and then fluorine gas. I'm assuming this is theoretical and you're not actually producing a balloon full of the gas, as hydrogen is very flammable and HF and fluorine are toxic.

Here's a quick way to find the density of a gas:

At STP, density = molar mass /22.4 L/mole

Recall that 22.4 is the volume of one mole of any gas at STP. Since molar mass is grams per mole, moles cancels out leaving grams/L.

You can approximate the density of air by assuming that it is 80% nitrogen and 20% oxygen, which is pretty close to its actual composition:

.80(28 g/mol) + .20(32 g/mol) = 28.9 g/mol

the density of air would therefore be approximately 28.9/22.4 = 1.29 g/mol.

Any gas with a molar mass less than that of air will also be less dense than air.