Hi Melinda,

 

I used SF6 for demos in my classes.  Teaching mainly in community colleges, we did not keep large cylinders of gases.  For SF6, I used lecture bottles. When using a lecture bottle, particularly with SF6, make sure the valve is closed tight after use as it will leak out - so double checking to make sure the valve is closed is imperative.  SF6 is expensive.

 

SF6 is great for teaching gas density.  I had balloons filled with hydrogen, helium, nitrogen, oxygen, and SF6.  They were as close to the same size as I could get them. All precautions with flammable gases were taken.  Students would be lined up in the front of the lecture hall, or classroom, holding the balloons.  They would release the balloons simultaneously.  As expected, hydrogen and helium balloon would rise up, but at different rates, the rest would fall downward.  Having string attached to the ligher balloons, they could be retrieved and their relative rates of assent could be observed.  We would retrieve the other balloons and observe their rates of fall.  Of course, the SF6 balloon fell like a "lead balloon".   

 

Try a game of catch with gas-filled balloons.

 

If you allow gas-filled balloons to sit somewhere undisturbed, the SF6 filled balloon will not deflate due to diffusion of the gas through the rubber.

 

You can also weigh a balloon filled with SF6, the buoyancy due to the surrounding air will be minimal.  It's best to weight gases in a heavier "container" such as an evacuated football or basketball to eliminate buoyancy effects.

 

It's a common demonstration to inhale some helium and speak.  Your voice is higher due to the rate of vibration of your vocal cords.  If you are assured your SF6 is pure, you can inhale it and your voice will be deeper.  (There are YouTube videos of this.) You will have to force remaining SF6 from your lungs.  You should only do this demo once.  Never allow another individual to do this.

 

 

You can pour SF6 from a beaker into another container, such as a small fish tank. in a way similar to pouring CO2.  You can float soap bubbles on the gas (I commonly did that with CO2 from a bed of dry ice on the bottom of the fish tank.) or a small "boat" made from paper or Al foil.

 

As usual, it is imperative to know what you are working with and to test all procedures with a colleague present before doing them in public.

 

Best regards,

 

David Katz

 

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From: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU> on behalf of Melinda Box <melinda.box**At_Symbol_Here**GMAIL.COM>
Sent: Thursday, March 16, 2023 7:53 AM
To: DCHAS-L**At_Symbol_Here**Princeton.EDU <DCHAS-L**At_Symbol_Here**Princeton.EDU>
Subject: [DCHAS-L] SF6 for demonstrations

 

Hello, everyone,

 

I have been tasked with investigating procedures for use of SF6 for lecture demonstrations. So I wanted to check in with you all to find out if you have any experience with supplying or supporting this demo and if so what tips, pointers, precautions, and/or prohibitions you might be willing to pass on.

 

Any help or info much appreciated, 

Thanks,

Melinda Box, MEd, CCHO

Elon University

Chemistry Dept Lab Manager

(336) 278-6225

 

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