Piranha solution
[1] Because the mixture is a strong oxidizing agent, it will decompose most organic matter, and it will also hydroxylate most surfaces (by adding –OH groups), making them highly hydrophilic (water-compatible).
This means the solution can also easily dissolve fabric and skin, potentially causing severe damage and chemical burns in case of inadvertent contact.
[5][6] This minimises the concentration of hydrogen peroxide during the mixing process, helping to reduce instantaneous heat generation and explosion risk.
Sintered glass also tends to trap small solid particles deep inside its porous structure, making it difficult to remove them.
Where less aggressive cleaning methods fail, piranha solution can be used to return the sinter to a pristine white, free-flowing form without excessive damage to the pore dimensions.
The dehydration process exhibits itself as the rapid carbonization of common organic materials, especially carbohydrates, when they enter in contact with sulfuric acid.
[12] With respect to organic residues such as thin films or wax, this results in the formation of carbon compounds rich in C=C double bonds.
A last secondary contribution to the piranha solution cleaning is its high acidity, which dissolves deposits such as metal oxides, hydroxides, and carbonates.
For substrates with low tolerance for acidity, an alkaline solution consisting of ammonium hydroxide and hydrogen peroxide, known as base piranha, is preferred.
The second and more definitive rationale for the name, however, is the dissolution ability of piranha solution, capable of "eating anything", especially elemental carbon in the form of soot or char.
It should never be stored in a closed receptacle because of the risk of gas overpressure and explosive burst with spills (especially with fragile thin wall volumetric flask).
When cleaning glassware, it is both prudent and practical to allow the piranha solution to react overnight taking care to leave the receptacles open under a ventilated fume cupboard.
While some institutions believe that used piranha solution should be collected as hazardous waste, others consider that it can be neutralized and poured down the drain with copious amounts of water.
[5][15][16] Improper neutralization can cause a fast decomposition, which releases pure oxygen (increased risk of fire of flammable substances in a close space).
