Gary
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Conc Sulphuric Acid- the undisputed 'King of the Chemical World'.
After watching some interesting Nurdrage videos on Youtube, I would like to have a go at making (or purchasing) conc. sulpuric acid.
It is such a useful reagent, since it can be used to synthesise many other important reagents.
In the past, I've used 98% sulphuric, drain cleaner grade, of acceptable purity (no added dyes or surfactants) to synthesis HCl, chlorine gas,
manganese heptoxide, acetic acid, boric acid, silicic acid,nitric acid, metal sulphate salts (copper sulphate, etc).
However, this source has dried-up, so I now need to make it by electrolysis of copper sulphate (as demonstated in the Nurdrage video) or purchase it.
I have found a new potential source; it is of 91% concentration and is contaminated by a red dye additive (rhodamine red??). Is 91% concentration
strong enough to synthesise halogen acids (HCl, HBr, HI) by reaction with the corresponding halide? Would it pass the classic sugar dehydration test?
I suppose I could concentrate it further by heating on a hot plate until the white fumes of sulphur dioxide or trioxide are evolved; perhaps the
oxidising action of hot, conc. sulphuric acid might oxidise the red dye to carbon dioxide gas or a carbonaceous residue that is easily removed by
filtration through a glass frit?
Would the dye have much negative effect on my reactions? Could it be oxidised with hydrogen peroxide? Or would activated carbon remove it?
If I were to prepare sulphuric acid by electroloysis of copper sulphate, is the choice of electrode material critical?
[Edited on 18-11-2010 by Gary]
[Edited on 18-11-2010 by Gary]
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hissingnoise
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| Quote: | | If I were to prepare sulphuric acid by electroloysis of copper sulphate, is the choice of electrode material critical? |
I tried it once using a Pt/Ir wire as anode and it worked well.
The cathode was a gouging rod and as the reaction progressed, copper built up warty nodules on the cathode until all colour had left the solution.
I assume a PbO2 anode would work as well and possibly MMO anodes too.
A graphite anode just might work but there's a good chance that it would be slowly oxidised during the reaction. . .
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entropy51
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Quote: Originally posted by Gary  | Is 91% concentration strong enough to synthesise halogen acids (HCl, HBr, HI) by reaction with the corresponding halide?
Would the dye have much negative effect on my reactions? |
It's strong enough to make HCl, probably too
strong to make HBr (oxidation to Br2), and sulfuric is not normally used to make HI because of oxidation to iodine. H3PO4 is normally used to make
HI. There's a paper posted on the forum on the proper dilution and method to make HBr.
The dye won't interfere with the types of reactions you mention. The question is WTF else did they put in it?
I've bought excellent drain opener and lousy drain opener, but none of it has ever been so lousy that you couldn't use it for something. (It
really does unclog drains.)
Boiling down H2SO4 is a bad idea. In addition to the usual burn hazards, inhalation of H2SO4 mists is known to cause cancer of the larynx.
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MagicJigPipe
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Do it outside or in a hood? Or with very adequate ventilation?
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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Gary
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My amateur home lab is not at the level of sophistication of being equipped with a fume hood (although it's something I will consider in the future),
so I would have to carry out such work in my back yard/garden, like I have in the past.
Perhaps the acidic mist could be passed into an alkaline scrubbing solution?
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Sedit
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Its no doubt possible but the heat generated from neutralization and the idea of keeping a hot concentrated acid near a hot alkaline bottle is abit
fearful. I use to perform this operation all the time in an open glass bowl outside until I located a better over the counter source of 97.8% Sulfuric
acid. The "mist" isn't so much of an issue its when it gets to that super high concentration and starts to release Sulfur oxides that it becomes an
issue. They will mix with atmospheric H2O and leave you with a very nasty and dense cloud of Sulfuric acid to deal with.
Prior to boiling it down I suggest the addition of a few ml of 35% H2O2 and your dye will all but vanish leaving you with crystal clear acid. The dye
should not mess with most synthesis I just enjoy the fact that with the dye gone I can now watch for any color change that may take place in the
reaction without the dye interfering.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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