Talk:Piranha solution

Source Material

Large sections of this article, particularly the preliminary paragraph and the "Mechanism of action" section seem to have been lifted from this web page. Is this a case of wikipedia plagarizing the web, or vice versa? Does anybody have the tools to tell the difference? Is the solution to rewrite this page, eliminating some of the jargon that lead me to that site and maybe citing it in the references? Thought I'd ask before ripping apart the text. Zolot (talk) 16:07, 28 November 2012 (UTC)

Another issue is that none of the mechanism of action section is cited, and as noted before, the chemistry seems implausible at best. I'm currently researching the subject, so if I find a good source I'll come back and clean up the section. Otherwise, it may be best just to delete the section. No information is better than wrong information in my book. --Heptazine (talk) 14:27, 12 December 2012 (UTC)

Similar

isn't "Peroxymonosulfuric acid" the same thing?

I don't think so, primarily for this reason (thanks to rw): piranha solution ages and becomes less effective over time, presumably due to the formation of peroxymonosulfuric acid. I'll try to add a bit about that later (but anyone else? feel free!) --Terry Bollinger 03:39, 27 July 2006 (UTC)

It is chemically identical. H2SO5 is the product in both reactions. Caro's acid, piranha solution, or peroxymonosulfuric acid decomposes rapidly and is therefore only produced in situ and immediately prior to use.SuperFluid 21:49, 6 July 2007 (UTC)

Handling

{{Hazard O Oxidizing}}

NONE of the following should be taken as professional NOR credible advice / information ALWAYS refer to authentic OSHA HAZMAT guidelines

There are some things that, just because you can do it, doesn't mean you should do it
—Ian Malcolm, Jurassic Park

"One must always add the peroxide to the acid, not the other way around."
Shouldn't that be the other way around? i.e. First rule of chemistry class is NEVER mix anything into an acid.

I agree with the poster above. I often use piranha solution to clean glassware and I always pour the sulfuric acid onto the hydrogen peroxide solution. The idea being that because sulfuric acid has a sizeable enthalpy of mixing, i.e. it heats up when diluted. So when you add something, your small amount of water heats up and will boil and splash and if you do it the other way round you have more water to absorb the heat so you will diminish splashing. Another useful thing to know is to use a big enough beaker, at least twice the volume of the piranha solution you want to make. 134.58.253.113 15:56, 15 February 2007 (UTC)

I have mixed it using both methods and have never experienced any sort of problems with boiling over or splashing, as long as the addition is done slowly and at RT. For simplicity, I instruct people to follow the "AAA" rule--always add acid (when diluting acids). This is simply for consistency and so that you do not initially make a very concentrated solution of acid by adding a small amount of diluent.SuperFluid 21:58, 6 July 2007 (UTC)

I disagree; I believe adding the peroxide to the acid is the safer method. Yes the exothermic enthalpy of mixing is an issue (and one should be careful that it does not splash out of control), but the bigger safety issue is preventing explosions. The likelihood of a hydrogen peroxide solution detonating depends on the concentration of hydrogen peroxide. For this reason, in three component systems with organics, water, and hydrogen peroxide, the hydrogen peroxide is always added last to minimize it's concentration. While I can't be certain, I would assume the same rule of thumb would hold true for piranha solutions. Heptazine (talk) 22:00, 12 October 2012 (UTC)

The two sources cited contradict each other. One says to add peroxide to acid, and the other says to add acid to peroxide. Here at UT we add acid to peroxide. — Preceding unsigned comment added by 128.62.209.138 (talk) 20:17, 1 August 2017 (UTC)

• You add the most vindictive component gradually to the relatively more benign, thus the concentration of it being at its lowest. For concentrated acids, this is almost always the acid, thus you add the acid to the water.

For concentrated hydrogen peroxide though, the roles are reversed (and a few other compounds with a "per-" involved. So you add the peroxide to the acid instead. If you wish, this is a proof that there's no good way to mix a piranha solution, and thus you just shouldn't ever make it. Andy Dingley (talk) 16:23, 15 November 2018 (UTC)

Do it like a chemist oughta: add the acid to the watta'
If your life is far too placid, add the watta' to the acid.

German mnemonic Erst das Wasser, dann die Säure, sonst geschieht das Ungeheure ("First water, then acid, otherwise a monster will appear")

Equation

I believe the "Chemistry" section needs attention. To my knowledge, the equation is wrong and should be written to reflect the formation of H2SO5, not elemental oxygen. The NASA reference to atomic oxygen does not have bearing in aqueous chemistry. Strong acids (and bases) are known to clean organic residues from glass and other surfaces. H2SO5 is a very strong acid. There is no reference (that I have seen) for the formation of atomic oxygen in aqueous solution.SuperFluid 22:20, 6 July 2007 (UTC)

The chemistry does look bizarre and the NASA reference is irrelevant (removed). Expert tag added. 84.92.241.186 20:08, 19 October 2007 (UTC)

The solution would most likely contain sulfuric acid, peroxysulfuric acid and free H2O2 in equilibrium. An educated guess, though, would place the actual oxidizing agent as the protonated H3O2+ cation, which - by virtue of its electophilicity - can be attacked even by weak nucleophiles such as benzene or other aromatics in the fashion of epoxidation reactions, or hydride donation from hydrocarbons (the C-H sigma bond acting as a nucleophile) to give water and a carbocation.--Triflic Anhydride (talk) 10:05, 18 October 2009 (UTC)

As a further note, I would like to correct Superfluid regarding the strength of H2SO5 as an acid; it is most likely weaker than sulfuric acid because of the alpha effect increasing backdonation into its orbitals and making it harder to delocalize negative charge. Its oxidizing power comes not from its strength as an acid (though H+ is still a good oxidizing agent), but a combination of its weak O-O bond and good leaving group (bisulfate).--Triflic Anhydride (talk) 10:21, 18 October 2009 (UTC)

The equations are clearly in error - at one point an extra carbon appears out of thin air (reaction of the O. with C=C). Also they're inconsistenat as to whether they label the carbons or not, with no logic for the inconcistency present. 128.40.76.3 (talk) 09:49, 23 July 2012 (UTC)

Stoichiometry?

What is "a 3:1 mixture of ammonium hydroxide (NH4OH) with hydrogen peroxide"? According to the article on "ammonium hydroxide" this term is used for aqueous ammonia in any concentration. So how do I prepare a 3:1 mixture of aqueous ammona (concentration unknown?) with hydrogen peroxide? Beryllium-9 (talk) 11:01, 29 February 2012 (UTC)

Yes the article is unclear. It is a 3:1 mixture, by volume, of the common commercial grade of ammonia (28-30 wt %), and the common commercial grade of hydrogen peroxide (30 wt %). --Rifleman 82 (talk) 19:00, 29 February 2012 (UTC)

Current version contains nonsense?

"Piranha should be prepared by adding the acid into the acid, not the other way around" What? I see that there's been some disagreement about how it was before, but the way the article is currently written is clearly wrong. 70.72.163.248 (talk) 04:31, 16 March 2012 (UTC)

Etymology

It would be nice to have an etymology. This would probably require historical research (like the rediscovery of the first emoticon) in order to find the person who (possibly) named it after the ravenous fish, and why. ArthurDent006.5 (talk) 12:06, 28 July 2013 (UTC)

I agree that etymology would be a good addition to this page. AlexanderMSOE (talk) 13:58, 22 March 2021 (UTC)

Done. fgnievinski (talk) 06:53, 4 August 2023 (UTC)

Safety

Am I the only one who thinks that this article is written such that it is giving advice on how to execute a potentially dangerous mixture? The name and chemical composition of the solution with a disclaimer that it is a potentially hazardous activity should be sufficient. There is no good reason to also tell readers to "heat this" or "let that sit overnight" -- especially on matters of opinion ("some feel it should be discarded as hazmat, others that it can be safely dumped with 'copious' amounts of water").

This article is just asking for trouble. — Preceding unsigned comment added by 72.29.164.238 (talk) 17:36, 20 August 2013 (UTC)

Agreed, especially with respect to fritted glassware. My understanding of the use of piranha solution with fritted glassware is one should "never ever ever do it." Far more serious explosion accidents have been documented than the two examples cited. As well as causing near-fatal injuries and permanent disabilities, the practice has destroyed laboratories and shredded fume hoods. Using piranha solution to clean fritted glassware is a huge safety no-no and this article should not be proposing it as reasonable practice in any lab environment. 198.179.125.170 (talk) 17:46, 14 November 2018 (UTC)

Is the problem with piranha and frits, or with piranha and frits which still have organic solvents on them? Certainly the second has a long and exciting history.

We should have coverage in this article according to what's sourceable. If there is a robust source out there either saying "don't do it" or else recording an accident of clear provenance with it, then we should include that. Andy Dingley (talk) 18:27, 14 November 2018 (UTC)

I agree with @Andy Dingley:.

Riventree (talk) 22:00, 17 July 2019 (UTC)

Containers: Glass only?

We might want to add a section: Are there containers other than glass that work for Piranha?

Self-interest disclaimer: I have a 400mm liebig that is too big to put in any of my glass containers.

Riventree (talk) 15:04, 1 July 2019 (UTC)

Yes, you can safely use PTFE containers to contain Piranha Solution (as noted by the Yale SOP for Piranha). It's a stubbornly unreactive substance that will happily remain inert in contact with things that eat through glass. As a rule of thumb it's safe for any chemical unless explicitly noted otherwise.

Bit late, but better late than never!

Xiongu (talk) 21:40, 2 May 2021 (UTC)

Base Piranha Solution

I noticed that this article only concerns acidic Piranha Solution (sulphuric acid + hydrogen peroxide). There is an alternative mixture that uses ammonium hydroxide (NH₃ (aq)) in place of sulphuric acid.

As far as I can tell, the two solutions are very similar, but have a few differences. The only difference I could find a proper source for is that basic Piranha is apparently slightly safer and requires heating to 60 °C to become reactive.

I have also seen anecdotes that it is useful for attacking residues that contain inorganic oxides that are insoluble in acids but are soluble in bases, such as some silica compounds or metal oxides (e.g. Al, W). Sadly I can't find any literature surrounding that.

Xiongu (talk) 23:39, 2 May 2021 (UTC)

HLC + H2O2 use(d) in PCB prototyping. Also called "Piranha Solution" ?

Common cleaning-grade HCL (around 14%) with the addition of some (around 10-25%) commercial grade hydrogen peroxide (35%/"perydrol") was used by me in the past (and many others, for sure) before the days of cheap prototype board production to etch copper with in-house "hand-made" prototype PCBs (after masking, exposing and removing the photoresistive layer with a basic solution). Adding always the oxidizer to the acid, I never noticed any heating effect with these grades (not measured with thermometer) but the mix started heating (along with coloring and fuming) with copper dissolving. PP containers show no signs of degradation after repeated use. Double Nitrile gloves are adequate for protection, directly handling the boards. With accidental minor touch with finger-skin rapidly followed by water rince, I felt nothing and no visible burns marks left. I do not know how widespread is this use, but it worked considerably faster and easier than Iron(III) chloride though I understand is more dangerous for many reasons (and for this, not suitable/recomended for amateurs). Is this also called "piranha solution"? — Preceding unsigned comment added by 2A02:214C:8601:D800:E13E:9280:524E:63E1 (talk) 11:56, 1 October 2021 (UTC)

Incorrect info in diagram

In the image of molecules at the top of the page, purportedly showing the species in solution, there are two molecules of H₂O₂, one molecule of H₂O, and H₂SO₅. However, the text at the bottom states the species in solution are H₂SO₄, H₂O, and H₂O₂. I see elsewhere in the discussion that H₂SO₅ does apparently form in solution, so I'm guessing it's just the text that's incorrect... but is it? If the solution itself is composed of just sulfuric acid and hydrogen peroxide, and if the reaction to produce peroxymonosulfuric acid doesn't happen immediately, then both species should be in solution, correct? In any case, the image and the text don't match and should be updated accordingly, though I'm not sufficiently knowledgeable to edit this myself. Lumberjane Lilly (talk) 19:16, 19 November 2021 (UTC)

Molecular model is wrong?

The representation of sulphuric acid in the image for this article contains 5 oxygen atoms, and is thus incorrect, showing a different molecule, H2SO5. 2604:3D09:680:580:A44A:B16E:DAE3:53B1 (talk) 20:26, 7 December 2021 (UTC)