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Darkfire
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[*] posted on 14-11-2003 at 22:29
Strongest Acid


Is HClO4 the strongest acid know to exist? or are there anything else, i was thinking so flourine acids might be stronger, triflouromethane sulphonic acid came to mind, im just wondering because it just doesnt sound true...

[Edited on 15-11-2003 by Darkfire]




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[*] posted on 15-11-2003 at 00:12


Olah's Superacid:
HSO<sub>3</sub>F
SbF<sub>5</sub>

I think they are a bit stronger, i think HClO<sub>4</sub> is considered strong because of is high reactivity with almost everything, than is pK<sub>a</sub>




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[*] posted on 15-11-2003 at 00:36


Do you mean strong as in high disassociation constant, or strong as in the everyday meaning of the word?



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Darkfire
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[*] posted on 15-11-2003 at 02:14


I mean i heard it at school by a chem teach and i didnt belive it to be true...

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[*] posted on 15-11-2003 at 06:53


Perchloric acid is considered a strong acid because it is alomost totally dissociated in aqueous solution.
The record for acid strength is held by a mixture of HSO3F and SbF5 (10%:90%)
It is about 10^15 times more acid than conc sulphuric.
This mixture is unofficially know as "magic acid", I gather it earned this name when someone saw it dissolving a candle.
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[*] posted on 15-11-2003 at 14:18


I hear of perchloric acid as being the strongest 'common' acid. Like people have said before there are superacids. These are much more powerful but they are found less frequently in labratory. I believe one definition of a super acid is any acid that can make concentrated sulfuric act as a base.



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[*] posted on 16-11-2003 at 15:28


Once you add water the strongest acid present is H3O+ (or some such) so, for a lot of things, it doesn't matter. Permanganic acid HMnO4 should be comparable in strength with perchloric, but I don't fancy working with it.
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[*] posted on 17-11-2004 at 07:32


A new stongest acid has been discovered / developed / isolated:

http://www.spacedaily.com/news/materials-04zzx.html

It discusses the discovery of carborane, and also mentions that fluoro-sulphuric was the previous strongest acid known. Anyway, some interesting reading for you all. Maybe.




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[*] posted on 17-11-2004 at 08:59


Holy crap, "Reed and his research group want to add hydrogen ions to Xe atoms "because it’s never been done before."

I think I have a new challenge, and so do all of you.




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[*] posted on 8-7-2015 at 20:29


In Angewandte Chemie International Edition. - 2014. - Vol. 53, No. 4. - pp. 1131-1134 described acid stronger that previous H(CHB11Cl11). New acid has formula H(CHB11F11) and reacts with hexane at ambient temperature.
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[*] posted on 8-7-2015 at 21:32


Interesting subject.


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[*] posted on 9-7-2015 at 01:45


HClO4 is the strongest acid that can exist in aqueous solution. It is, however, sometimes considered a superacid because it forms an isolable hydronium perchlorate salt, and any aqueous solution of HClO4 is actually a solution of hydronium perchlorate.
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[*] posted on 9-7-2015 at 16:01


I know a lot of acids that stronger perchloric acid and can exist in aqueous solution.

What Hammet constant does (CF3SO2)3CH has?

Is there free pentacyanocyclopentadiene (not salts)? 1,2,3,4,5-Pentacyanocyclopentadiene stronger HClO4 and H2SO4.
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[*] posted on 9-7-2015 at 16:06


Quote: Originally posted by chemister2015  
I know a lot of acids that stronger perchloric acid and can exist in aqueous solution.

It is very nice that you know a lot of acids that are stronger.

Please name them along with their pKa values so we can all know.




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[*] posted on 9-7-2015 at 16:21


Reference please?
[edit] what aga said...



[Edited on 10-7-2015 by Molecular Manipulations]




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[*] posted on 9-7-2015 at 16:49


Quote: Originally posted by Molecular Manipulations  
Reference please?
[edit] what aga said...



https://en.wikipedia.org/wiki/Superacid

Plenty are much stronger than HClO4, so strong pKa becomes meaningless.

Carborane acids:

http://www.nature.com/news/2004/041115/full/news041115-5.htm...

https://en.wikipedia.org/wiki/Carborane_acid

Protonates benzene, that stuff!


[Edited on 10-7-2015 by blogfast25]




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[*] posted on 9-7-2015 at 17:50


I was asking for a ref from ave, I had no doubt there are stronger acids than perchloric acid.



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[*] posted on 9-7-2015 at 17:59


HClO4: pKa (H2O) = -10, pKa (CH3COOH) = 2.7, pKa (ClCH2CH2Cl) = -13.0, H0 (100%) = -15.

HPF6 pKa (H2O) = -20
HI pKa (H2O) = -11
C5H(CN)5 pKa (H2O) = -11
HSO3Cl pKa (H2O) = -10.43

CF2(CF2SO2)2NH pKa (ClCH2CH2Cl) = -13.1
O2NC6H4SO(=NSO2CF3)NHSO2CF3 pKa (ClCH2CH2Cl) = -13.1
HB(CN)4 pKa (ClCH2CH2Cl) = -13.3
(FSO2)3CH pKa (ClCH2CH2Cl) = -13.6
(CF3SO2)2CHCN pKa (ClCH2CH2Cl) = -14.9
C5H2(CN)4 pKa (ClCH2CH2Cl) = -14.9
1,1,2,3,3-pentacyanopropene pKa (ClCH2CH2Cl) = -15.3
(CF3SO2)3CH pKa (ClCH2CH2Cl) = -16.4 (estimated)
CF3SO(=NSO2CF3)NHSO2CF3 pKa (ClCH2CH2Cl) = -18 (estimated)

H2S2O7 H0 = -15
HSO3F H0 = -15.07
HSbF6 H0 = -15 - -20

There are a lot of very strong acids that I don't know pKa.
carborane-based: H(CHB11Cl11), H(CHB11F11), H(CHB11Br11), H(CHB11H5Cl6), H(CHB11H5Br6), H(CHB11H5I6), H(CHB11(CH3)11), H[Co(C2B9H8Cl3)2], H(CHB11(CH3)5Br6), etc
HN(SO2CF3)2
HB(C6F5)4
H7P(W2O7)6
...
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[*] posted on 9-7-2015 at 18:00


Quote: Originally posted by chemister2015  
I know a lot of acids that stronger perchloric acid and can exist in aqueous solution.


Perchloric acid cannot exist as such in aqueous solution, because it reacts 100% to give hydronium ion and perchlorate ion.




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[*] posted on 9-7-2015 at 18:45


Quote: Originally posted by DraconicAcid  

Perchloric acid cannot exist as such in aqueous solution, because it reacts 100% to give hydronium ion and perchlorate ion.


Hence NaCl cannot exist as such in aqueous solution, because it gives sodium-ion and chloride-ion :D
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[*] posted on 9-7-2015 at 22:46


Quote: Originally posted by blogfast25  
Quote: Originally posted by Molecular Manipulations  
Reference please?
[edit] what aga said...



https://en.wikipedia.org/wiki/Superacid

Plenty are much stronger than HClO4, so strong pKa becomes meaningless.

Carborane acids:

http://www.nature.com/news/2004/041115/full/news041115-5.htm...

https://en.wikipedia.org/wiki/Carborane_acid

Protonates benzene, that stuff!


[Edited on 10-7-2015 by blogfast25]


How does carborane acid behave when you try to dissolve it in water?
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[*] posted on 10-7-2015 at 10:13


The carboranes are my favorite of the stronger acids, and DABCO being my favorite superbase.
Fave. superbases anyone?
Speaking of carboranes, does anyone else think there are more crystalline alkanes besides the two or three ever made, cubane and one other?




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[*] posted on 10-7-2015 at 14:55


Fluoroantimonic acid has a pKa of -25. It is also interesting because it is an ionic liquid.
https://en.wikipedia.org/wiki/Fluoroantimonic_acid

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[*] posted on 12-7-2015 at 12:15


I don't like the term "super-acid".

(I hope this hasn't been mentioned above)

There is the term of solvoacid and solvobase which isn't really taught. I hope it's called solvo acid in English, too.
Basically any Acid or better Solvent that has a Proton somewhere can dissociate. And there is always a
Solvent(+H)+ and a Solvent(-H)- Form. In Water this is H3O+ and OH- .

An Acid is a substance that can donate an H+ to the solvent and a strong acid will fully transfer all Protons to the solvent. But the pH is limited to the solvo-acid so the protonated form of the solvent.

"There can't be any stronger acid present in solution than the protonated solvent". So acids like HCl or Perchloric Acid are more or less "super acids" to water.

Now if you use Ammonia as solvent the Ammonia will also autodissociate. Then acetic acid would be a "super acid" in liquid Ammonia. A very common effect where this is used - and most people don't really know about that - is when you dissolve a hardly soluble Sulphate in excess conc. Sulfuric Acid. This works because there is always some protonated Sulfuric Acid in the conc. Acid itself (due to autodissociation). And that Acid is strong enough to even protonate sulfates so they become soluble.


Back to the question. There are strongers acids then Perchloric Acid. I think organic chemistry should be able to find some stronger ones. If you change functional groups you could probably create some strong acids. But the most common one is the Antimony one.
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[*] posted on 12-7-2015 at 12:33


What you are talking about is referred to as the "levelling effect" of a solvent. In water no acid will be stronger than H3O+ (or however you want to represent a solvated proton.
Similarly, no base will be stronger than hydroxide.

Acids and bases that are fully dissociated in any given solvent are referred to as strong acids or bases (so, acetic acid is a weak acid in water, but a strong acid in liquid ammonia).
Since there's already a termfor those fully dissociated acids, it's redundant to use the term "superacid" for them as you seem to want to.

However, it's not unreasonable on a practical basis to have a term for really strong acids. Stronger than sulphuric is an arbitrary cut off point, but it's what someone chose.
If you don't like the term superacid, don't use it.
But please don't use it where you actually mean "strong acid".

[Edited on 12-7-15 by unionised]
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