The mixture piranha is a mixture with variable concentration of Acid sulphuric (HSO) and of Hydrogen peroxide (HO). This one is used to produce the Acide of Caro and to clean the organic residues on the substrates.

Preparation

There do not exist ratios of sulphuric acid and hydrogen peroxide fixed for the piranha mixture: so in laboratory one usually uses three volumes of sulphuric acid for one of hydrogen peroxide, it is perfectly possible to prepare mixtures with 4/1, 5/1, or 7/1. It is also possible to substitute the sulphuric acid by Hydroxyde of ammonium (NHOH).

The piranha mixture prepares by slowly pouring hydrogen peroxide in the sulphuric acid under hood with protections. The reaction is exothermic and the mixture is often put to boil during several minutes. During this one is formed the Acide of Caro, powerful oxidizing.

Storage

Acid of Caro, as well as the hydrogen peroxide being not very stable, the piranha mixture is generally effective only in the hours or the days following its manufacture and it is little recommended to it stoker or to use it too a long time after preparation. In industry, the piranha mixture generally is prepared on the spot, used as of its preparation, then destroyed.

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