From: Geoff Ruth (gruth@leadershiphigh.org)
Date: Sun May 11 2003 - 10:30:41 PDT
Message-Id: <p05200f05bae42ee8d3de@[192.168.1.25]> Date: Sun, 11 May 2003 10:30:41 -0700 From: Geoff Ruth <gruth@leadershiphigh.org> Subject: Re: hydrogen gas
Thanks, Roy, for the advice on generating H2 gas. I was able to
create a smallish balloon of H2 using the Zn/acid method suggested
by Roy. Below are some tips that I found in doing it:
* I actually found that mossy Zn didn't work -- it was too slow in
generating H2 to fill the balloon. Instead, I used some powdered Zn
that I had, which worked well.
* I used H2SO4 instead of HCl (since I had some handy in the acid
cabinet) and I inadvertently created H2S as well as H2. I later
looked up all voltaic potentials in the CRC and found the complicated
mechanism that H2S was generated from the reaction. So it's important
to use HCl, because it's much less of an oxidizing agent than either
H2SO4 or HNO3.
* Also -- I did the whole thing in a tiny 50mL E flask, to minimize
air space and therefore decrease the pressurization problem Roy
mentioned.
-- Geoff
>Hi Geoff.
>
>Depending on how much you need, this may work. We
>often show the limiting reactant concept by adding
>successively larger samples of baking soda to
>identical volumes of an acid solution. The baking
>soda sample is shown, then placed in a balloon, which
>is then attached to cover the mouth of a flack with
>the acid. Tipping the baking soda into the acid
>initates the reaction, with the CO2 trapped in the
>balloon. Perhaps you could use the same setup with
>magnesium ribbon or turnings in the balloon instead of
>baking soda? Also, most of us have more "mossy" zinc
>sitting around than you can shake a stick at. I think
>the zinc reaction may be too slow, so the magnesium
>reaction might be better. About 2.75 g of Mg (or
>about 7.5 g Zn) with 38 mL of 6M HCl has a theoretical
>yield that should fill a 10" balloon at room temp, but
>we know how theory goes, so you'll need more.
>(Actually, it would only fill the balloon if you had
>100% yield and if the stretching of the balloon did
>not add any pressure to the system.) Oh, by the way,
>probably NOT a good idea to try taking large
>quantities of H2 and mixing them with O2 before
>ignition. The combination produces a MUCH bigger
>bang. They do this demo at UCB in PSL (or whatever
>its new name is) and balanced amounts in soap bubbles
>would produce explosions large enough to produce shock
>waves throughout the lecture hall. There's another
>idea though -- generate the hydrogen and use either a
>stopper/tubing setup or a sidearm flask to attach it
>via rubber tubing to a soap bubble pipe. You can't
>hold the gas indefinitely, but if you just wanted to
>light off some hydrogen, that might be another way. A
>plus here is that any sound will be from the expansion
>from the combustion, not from the balloon itself
>popping. Happy experimenting.
>
>Roy Mayeda
>Sauk Centre HS
>Sauk Centre, MN
>
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