Acetylene lighter then air?

[The Crazed]

I was wondering if anyone knew if Acetylene is lighter (less dense) then air... I hade made some and was wondering if it would rise if I put it inside of a balloon to have some fun.

[megalomania]

According to the Merck Index acetylene is slightly less dense than air. 0.90 to air's 1.0

[Flake2m]

I had this idea for a charity fair that expolited ethyne's (acetylene) density.

I could my friend oxy set and sell ballons at a charity fair. the contain either O2 or ethyne. You can guess what happens next...

[metafractal]

Why not just use H2 (hydrogen gas)? As you probably know, it can be obtained by adding any metal (the more reactive the better) to any acid. Its much lighter than air (helium baloons used to be hydrogen baloons until a blimp filled with hydrogen exploded igniting all of hindemberg), and violently flammable. While it does not hold as much energy as acetylene, the molecule is smaller and therefore burns quicker so the energy/time almost evens out. Have a look around, there are plenty of threads about this around here...

[Flake2m]

ethyne is easier to obtain.
Also, alot of people know the hydrogen gas is flammable but as for ethyne; well they'll just have to find out the hard way. :cool:

[Tuatara]

I wouldn't say ethyne was easier to obtain!. H2 is most easily made by chucking scrap Al into NaOH soln. I do this all the time for my kids. Watch it though, the rxn is exothermic so it can run away on you and fill your balloon with boiling caustic foam instead:D

[Anthony]

Tuatara, if you bubble the H2 produced into another bottle filled with cold water (and the balloon attached to the top of it), you condense out any steam or froth. Giving a lighter, fuller, firmer bust, err balloon... ;)

When I did it, it really made a big difference to how well the balloons floated.

[xyz]

I have a hydrogen generator setup that is similar to the one described by Anthony, only I also have a cooling bath to stop the reaction going too quickly. It is an empty chlorine granule bucket that has a hole cut in the lid for the top of the reaction vessel (2l bottle) to poke out. The hydrogen then goes through a tube where it is bubbled through water in a second bottle and then enters the balloon.

[Flake2m]

I was referring to how esay it is to purchase ethyne gas. Hydrogen is very easy to produce but in the quanties you'd need for a craft fair. A hydrogen generator would not be enough. Also if you by a tank of ethyne you have a legimate use for it as lots of people like doing metal work. Hydrogen does not have very many household or business uses.

[Tuatara]

Taking Mega's density data (thanks), and making the assumption that a ballon weighs 5g it turns out that the balloon needs a volume of 40 litres to achieve neutral buoyancy. Now thats a pretty big balloon - which barely floats, and has no string!

The balloon weight is a guess - I was going to weigh some but we've run out.

I think this explains why hydrogen and helium make the best 'floaty' balloons.

Edit: More data

Air density (standard) 1.24 kg/m^3
H density 0.0899 kg/m^3
He density 0.179 kg/m^3

and a link Balloon lift calculations (http://www.aucegypt.edu/students/quark/Research/balloon.htm)