Aluminum foil floating on Sulfur Hexafluoride gas

An open-top aluminum foil box sits in an aquarium as an invisible (and odorless) gas is poured into both containers. This quiet five and a half minute video makes for a wonderful discussion prompt: What is happening here? Why does the aluminum foil ‘boat’ start to float? And what’s happening when the aluminum foil sinks?

Watch this demonstration of aluminum foil floating on Sulfur Hexafluoride (SF6) gas, an anti-Helium of sorts that is also “the most potent greenhouse gas we know.” Some details from Steve Spangler Science:

Sulfur hexafluoride (SF6) is inert (won’t mix with anything) and non-toxic. It can do some surprising things even in small quantities. Except, don’t try these at home for two reasons:

• You have to be trained in its correct use and handling
• SF6 is quite expensive

SF6 is a gas that’s heavier than air. Like carbon dioxide (CO2), SF6 sinks and fills any low spots first… Like CO2, sulfur hexafluoride is dense enough to allow things to float on it, too. You can fold an aluminum foil boat that sits right on the top of a layer of SF6 as though it were floating on water.

Update: Reason three via @AlomShaha: Educators and science communicators are moving away from this demonstration for reasons of environmental safety. From The Conversation:

“SF₆ is a man-made, colourless, odourless gas and is indeed the strongest greenhouse gas in the Earth’s atmosphere. On a per molecule basis, SF₆ is approximately 23,500 times more effective at trapping heat than CO₂ and lasts in the atmosphere for about 1,300 years.”

Luckily we can learn from existing video demonstrations. We’ve also enjoyed this one: Aluminum foil boat floating on a sulfur hexafluoride sea.

Plus, watch these excellent science demonstration videos next:
• Demonstrations of the Coanda Effect
• What happens to balloon animals in liquid nitrogen?
• The Hidden Complexities of the Simple Match
• Use a 9-volt battery to break water into its elemental components

Bonus: Homemade demonstrations by science teacher Bruce Yeany and the Royal Institution’s ExpeRimental DIY science video series.