[armourer]

Hey guys,

I'm trying to repeat the boat floating on Sulfur Hexafluoride experiment for an AP Chem final project.
http://youtube.com/watch?v=YRAhO4XESBU

We have several Al foil boats of varying weights, 26 L of SF₆, a cardboard cover, and a watertight fish tank.

So far, using the attached blower nozzle and the cardboard cover, we've been unable to duplicate the experiment.
Even the lightest foil boats won't float, and we suspect there simply isn't enough SF₆ inside the tank.
Any ideas?

Could we be filling it too fast (i.e. use a hose at a lower flow rate rather than the blower nozzle)?

Any advice?

Thanks a bunch,

Evan

[constant thinker]

Filling it too fast could be a problem like you said. I'd try a lower fill rate if I were you.

Good luck, and try to get some footage/pictures. It'd be cool to see more people trying it.

[enahs]

Yes, filling to fast will just use a current to displace it. Also, if your gas is small you can always start work out the appropriate flow rate by just filling up a glass with the sulfur hexafluoride, and making a tiny "boat".

The best way would be a slow slow fill rate, and put the hose at the bottom of the tank while it is filling.

[woelen]

One could try this with Cl2 instead of SF6. Cl2 also is very dense, relative to air, and it is easy to make (one 20 gram tablet of swimming pool TCCA makes around 10 liters of pure Cl2-gas, cost only $0.50 or so). Of course, the toxicity of chlorine is a hurdle, but with some caution, it should be possible. This is something I will try on a good summer day, without too much wind, in an open place, outside!

SF6 of course is better, but I cannot obtain this, and if I could, it would be prohibitively expensive.

[Dude]

You should start with the basics:

1.  Given the density of air and sulfur hexafluoride, calculate the maximum weight of air / aluminum foil that will float given the dimensions of your aluminum foil container and then weigh your boat to make sure that it is "seaworthy". 
(mass of air + mass of foil / volume of foil boat) < density of SF6

2.  Make sure that the boat is absolutely air tight so that no SF6 leaks into the air space.

3.  What is the volume of your fish tank (hopefully < 26 L)?

3.  Fill very slowly from the bottom and avoid turbulence (which will whip air in and reduce the density).

4.  Due to diffusion, this is a quasi state.  You probably only have a couple of minutes before it sinks.

[hmx9123]

I'd like to see you be the one to put the aluminum boat into the Cl2 atmosphere!

I agree with Dude's assessment; the less turbulance you have, the better off you'll be.  Fill slowly from the bottom, and perhaps even get an outlet nozzle on the top so that you can 'push' the air out?

BTW, you can do a similar experiment with CO2.  If you put a piece of dry ice in the bottom of a loosely covered graduated cylinder, you can then 'pour' the CO2 onto a candle to extinguish it.  Pretty interesting.

[shelanachium]

There are stable non-toxic fluorocarbon gases even denser than SF6 (MW 146). These include perfluoropropane, C3F8,  (188); C4F10 perfluorobutane (238) and perfluorocyclobutane C4F8 (200) - I think the last at least is commercially available. For the ultimate try perfluoroneopentane C(CF3)4 (288). If you aren't worried about toxicity try tungsten hexafluoride WF6 (298).

I've often fancied getting some heavy metal band to try breathing one of these fluorocarbons to give the opposite effect to helium and produce a growling 'monster' voice!

Just seen someone do this with SF6 on You Tube! Click on youtube site in initial message and you'll get there!