Re: hydrogen gas

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From: ROY MAYEDA (roymayeda@yahoo.com)
Date: Sat May 03 2003 - 05:53:09 PDT 

Message-ID: <20030503125309.51761.qmail@web20420.mail.yahoo.com>
Date: Sat, 3 May 2003 05:53:09 -0700 (PDT)
From: ROY MAYEDA <roymayeda@yahoo.com>
Subject: Re: hydrogen gas

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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