Beanspike
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Mg + h2o
Hello friends, neighbors, chemists, and pyros:
While "playing" in my nice little homemade lab, I decided that I wanted to see how Mg reacted with water. I mixed a very small amount
of Mg shavings in a very small test tube and added water. I saw no initial reaction so I decided to see what an acid catalyst would do to it. That was
interesting... the glass got REALLY hot and I was left with a little bit of pinkish(the color of the h2so4) liquid, an acrid smell in the air, and no
more visible Mg shavings. Now I understand that this may be a simple question to most of you, but I'm not exactly sure what's going on. Is
it a reaction similar to what happens in toilet cleaner bombs (toilet bowl cleaner and aluminum foil)?
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bigbob
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The acid was not acting as a catalyst but rather as a reactant. Mg will react (albeit slowly, hindered by oxide layer) with water to form its
hydroxide, Mg(OH)<sub>2</sub>. The acid reacted with the Mg to form hydrogen and Mg sulfate as per this equation:
Mg+H<sub>2</sub>SO<sub>4</sub> ---> MgSO<sub>4</sub> + H<sub>2</sub>. The acrid smell was probably
an aerosol of acid created by the bubbling of the hydrogen through the solution. It's similar to those pressure devices in that both evolve a
gas, it was probably H<sub>2</sub> but no way to tell until we know what's in that toilet cleaner of yours. Good to see an interest
in chemistry, carry on. I suggest reading about the fundamentals of it so you are less likely to do something stupid and hurt yourself or others.
If everybody carried a gun, it\'d be a much more courteous world.
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Beanspike
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Thanks a bunch.
I took the fundamentals of chemistry last semester but unfortunately it was quite early in the morsning so I usually ended up not going.... I
didn't regret it until I started in the baby organic course. Now I have to go back and re-read alot of the stuff I learned before. I hope someone
can learn a lesson from me 
Anywho,
the toilet bowl cleaner "bomb" that I mentioned was aluminum foil mixed with a small amount of HCl solution in a 20oz bottle. When the HCl
reacts with the Al2O3 in the foil, the gas it forms that pops the bottle is H2. I think thats how it works anyways.
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Cappy
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When the HCl reacts with the Al2O3 in the foil, the gas it forms that pops the bottle is H2. I think thats how it works anyways.
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Actually:
2Al + 6HCl --> 2AlCl3 + 3H2
Aluminum quickly forms an aluminum oxide layer when exposed in air, but this layer is very thin and will only be a small amount of the mass of
aluminum foil.
Metals that form protective coatings in the atmosphere:
Al to Al2O3
Mg to MgO
Cu to CuCO3 (patina)
Ag to Ag2S (tarnish)
Iron oxide forms on iron, but it is too porous to protect the metal from further corrosion:
Fe to Fe2O3 (rust)
[Edited on 4/8/2003 by Cappy]
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Marvin
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The direct reaction is somewhat unlikley. Its more likley that the aluminium oxide is dissolved slowly by the HCl, and the exposed aluminium reacts
with whatever its in contact with, which will be mostly water formaing more Al2O3 (hydrated, which reacts faster with HCl) and hydrogen gas.
Dissolving the oxide is the limiting step in effect. Much better ways to dissolve aluminium, involve alkali hydroxides, which form aluminates, the
'draino' reaction for example.
[Edited on 8-4-2003 by Marvin]
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BASF
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By the way......want to make a hydrogen-balloon? 
The russians solved the task of filling a balloon with hydrogen in the russian-japanese war back in ....can´t remember....using NaOH solution on
aluminum junk.
I´ve tried that reaction a dozen times and it is much fun.....it is a very vigorous and hot reaction, and the warm hydrogen and the whole thing looks
like a thrust-nozzle working then  .
However, i have to admit that the major drawback of this way of making hydrogen is that the gas is saturated with water, so not ideal.
Montgolfière, if i remember right, was doing the task another way: he used 30-50% H2SO4 on iron filings to fill one of his balloons.
You can imagine that the gas so produced was quite dry, although the filling took longer.
-It just seems that the russians wanted a fast process for the filling instead.
HLR
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Beanspike
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an idea
I thought of making a little device to capture hydrogen... I was thinking the reaction(h2so4+Mg, Al+HCl, whatever) taking place in a bottle with a
tube attatched to the top, run the tube over to another bottle filled with h2o, and have a small hole right at the bottom of the bottle with another
tube in it, and hae the pressure of the reaction force the h2o out of the 2nd tube(or skip the second tube and bottle and use a balloon).
I had the whole thing nicley planned out, but then I realized I had no immediate use for hydrogen.
Bummer.
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Polverone
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interesting thing about Mg
Water + Mg is slow to react. I read in some inorganic reference or another that this is mostly because of the limited solubility of Mh(OH)2 in water,
and that the reaction with methanol was considerably more rapid. So one morning before I left for my classes I dropped a strip of magnesium in a test
tube of methanol. When I returned that afternoon, the magnesium was gone and there was a sort of semitransparent gel mixed with the methanol in the
tube. I thought this was pretty nifty... even if it doesn't have much to do with your question 
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Beanspike
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Hey I'm on here to learn what I can... anything that causes me to think and look for answers is great by me.
Mg+Methanol? would that create Mg(OH) and CH4(after it is balanced out)? or would it do something like Mg+CH3(OH) ---> H+CH3OMg?
All we need now is a use for the semi-transparent gel.
The reason I'm thinking of the reaction that creates CH3OMg is because when a carboxylic acid (such as CH3COOH) reacts with a base (such as NaOH)
you get a carboxylic acid salt:
CH3COOH+NaOH ---->CH3COO(-)Na(+) + H2O
[Edited on 9-4-2003 by Beanspike]
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