Making oxygen

[barquentine]

I ran an experiment this morning with my 9th grade students, to demonstrate the properties of oxygen. Of course first I had to show them how to make oxygen so I decided to use two methods:

1. H2O2 + MnO2. This worked OK and I quickly generated a litre of oxygen and filled a large Ehrlenmeyer flask. I did the glowing splint and magnesium ribbon demos.

 

Then I wanted to dem sodium metal in oxygen. I had used an awful lot of 3% hydrogen peroxide to generate the first litre and recalled that decomposition of KNO3 to KNO2 produces oxygen so I set up a distillation flask and began blasting it with a bunsen burner. No go!

Even with the burner flame playing directly on the glass all that happened was that the potassium nitrate melted but after 10 minutes - no oxygen. It would NOT decompose.

My question, how bloody hot does it have to get? After my trial I do not believe this is a viable method of generating oxygen in the lab, (before you mention it, no I don't have any potassium chlorate in the cupboard right now.)

Thanks

 

P.S. a chip of Na did not spontaneously ignite in pure oxygen; I had to trigger it by dropping burning Mg ribbon on to it, then it burned bright yellow.

[Gilded]

Sodium can have a thick oxide layer protecting it so the not igniting part isn't that weird, but I'm not really sure about the KNO3. It probably requires higher temperature to convert into nitrite than for just melting, but with a bunsen burner it should've been achievable. Weird.

[hermanntrude]

get stronger hydrogen peroxide, or even a lecture bottle of oxygen. commercial oxygen generators use sodium chlorate and iron powder... when ignited they produce oxygen at a steady rate... perhaps you could use that too.

 

sodium metal tends to form oxides and other things in air which prevents it from reacting when you want it to. to help with that, drop a drip of water onto it to get things going.

 

another good demonstration is the combustion of sodium in chlorine, which again, often requires a drip of water to start it, but goes like a bat out of hell when it goes.

[big314mp]

You could also look into an oxygen concentrator, that pulls O2 from the air. A used one may not be too expensive.

[barquentine]

Or maybe electrolysis will make enough ... I guess I could produce some in advance. I have an old computer psu at home, I could use for a supply, plus carbon electrodes. I'll try it. At least it will have the benefit of making H2 as well, since next after O2 I usually have fun making hydrogen. I'm lucky to have a well-equipped lab.

[hermanntrude]

the good thing about having bth hydrogen and oxygen is that you can fill balloons with both, and another with a mixture. the oxygen balloon won't do much, the hydrogen balloon will explode and the mixture balloon will blow up noisily and violently

[jdurg]

Another GREAT demo is to fill a ballon with two parts H2 an one part O2. Also, fill another balloon with just H2. Then, take a platinum wire and heat it up in a bunsen burner. Let it cool down a little bit so that it's not glowing any more but is fairly hot. Pop the H2 balloon with this wire. (Do some practice first so that the heat from the H2 doesn't ignite the H2. This will take a bit of time to get right). The H2 balloon should just pop but not ignite.

 

Now do this with the 2/3 H2 and 1/3 O2 balloon. Pt catalyzes the reaction between hydrogen and oxygen so the warm/hot Pt wire should cause the balloon to ignite with quite a bang!

[big314mp]

Can that be done with a cool platinum needle? Or does the platinum have to be warm.

[barquentine]

..I've tried the talking-in-a-helium-voice thing, so I thought would it be possible to do the same with hydrogen, or ... no that sounds like a stupid idea, there would be a risk of your lungs exploding like an extra on the set of an Arnold Schwarzeneger SF movie.

 

Actually I think I will see if the school will pay to get my miniature oxy-acetylene set refilled. I have a small trolley welding set, the acetylene is like a small propane bottle and the oxy looks like a miniature of the full size one, about 2 ft tall. Hmm, way to definitely decompose that KNO3. The stuff melted and that's about 330C but it wouldn't decompose (400C) so I deduce that the hot part of my bunsen burner flame probably is around 360 - 370C. Cool, real cool.

[big314mp]

That sounds awfully low for a bunsen burner...I would think you could at the very least get 1000+ C out of one:

 

http://hypertextbook.com/facts/1998/JamesDanyluk.shtml

 

You might have better luck if you can find potassium perchlorate.

 

How much nitrate did you use? I've only seen this demo done out of a large test tube, so perhaps there was too much to heat it properly?

 

I think disposable bottles of oxygen can be found in hardware stores in the tools section, if you want to look into that also. They would be with the welding supplies.

 

And I think that disposable helium tanks are pretty cheap also. I haven't seen any recently, but I used to have a few lying around, and they carried quite a bit of helium per tank. They were about the size and shape of a propane cylinder.

[jdurg]

Can that be done with a cool platinum needle? Or does the platinum have to be warm.

 

I'm not 100% sure of that. When I've done the experiment, the Pt has been hot, but not too hot to hold in your hands. If you have an ample supply of H2, it can't hurt to test it out a few times.

[pyrorower]

Not sure if anyone mentioned this, but I have made O2 by combining H2O2 and NaClO to form H2O, O2, and NaCl...

[Arthur Dent]

I guess the easiest and most inexpensive way to acquire oxygen is at any good hardware store:

http://www.canadiantire.ca/AST/browse/6/Tools/WeldingSoldering/Torches/PRD~0587575P/Worthington%252BOxygen%252BGas%25252C%252B14.1%252BOz.jsp?locale=en

You can get a bottle of O2 for 10 bucks, and with a slightly modified torch head, use it as an oxygen dispenser for your experiments. I use a setup like this with a propane bottle and my bunsen burner:

So this certainly could be applied to an O2 bottle. Always make sure to apply a bit of soapy water on the junctions to make sure there are no leaks!

- Robert

Edited June 19, 2010 by Arthur Dent