Keras
National Hazard
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Easy piranha solution
Since 30% hydrogen peroxide is not easy to acquire, at least in Europe where it is prohibited, for those who still have access to 98% sulphuric acid
and wouldn't risk heating it and mixing both reagents, I've been using sodium percarbonate for a while.
In the flask you want to clean, put half a gram or so of sodium percarbonate. Then gently drop a few millilitres of concentrated sulphuric acid at
r.t. The acid will almost immediately start to bubble. Hydrogen peroxide is released, and sulphuric acid neutralises the sodium carbonate, producing
carbon dioxide and water, into which sulphuric acid will dissolve. All these reactions are highly exothermic and will heat the mixture in situ. You
can even heat it further by adding a few drops of water. This forms a very effective oxidising solution, and has several advantages:
• It is much less risky than heating sulphuric acid and mixing it with 30% hydrogen peroxide
• You use only tiny amount of reactants. If you want to spare your sulphuric acid, I think this is definitely the way to go.
The action might be a bit slower than a true piranha solution, but left to cool for a few minutes, it will clean glass very effectively.
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Sulaiman
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Does this solution 'dissolve' carbon, organic tars etc. ?
CAUTION : Hobby Chemist, not Professional or even Amateur
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Keras
National Hazard
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I used it to clean a round bottom flask after a failed nitrosation. The walls were all full of tar. It worked quite well, yes. And it also cleaned my
poro-4 Büchner funnel.
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Texium
Administrator
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Mood: PhD candidate!
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You don’t
have to heat the sulfuric acid when making piranha solution. Adding the acid to the peroxide solution (even with the peroxide starting out at -20 C)
is exothermic enough to heat the solution very effectively.
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