Sciencemadness Discussion Board

why HO2 is a stronger acid than H2O2

chem_haruka - 19-5-2015 at 19:31

pKa(HO2)=4.88 pKa(H2O2)=11.8 pKa(HO)=11.9 pKa(H2O)=14(15.6)

elementcollector1 - 19-5-2015 at 20:34

What is "HO2" and where can I get some?

420MLGnOhEADsCOPEpro - 19-5-2015 at 21:00

Quote: Originally posted by elementcollector1  
What is "HO2" and where can I get some?

exactly what i thought when i saw this

a quick google search gives
http://en.wikipedia.org/wiki/Hydroperoxyl
>The hydroperoxyl radical, also known as the perhydroxyl radical, is the protonated form of superoxide with the chemical formula HO2

i would think that HO2 is more acidic because it's a free radical as opposed to H2O2 which is much more stable

j_sum1 - 19-5-2015 at 21:30

Quoth Wikipeda


HO2.jpg - 15kB

elementcollector1 - 20-5-2015 at 08:44

Ah, a radical. That explains it, then. And yeah, a radical is usually much more reactive than a compound.

woelen - 20-5-2015 at 22:56

HO2 is very unstable and only exists for a very short time. Salts of this acid, however, are quite stable and the potassium salt (KO2) can be purchased commercially. This salt is orange. When this salt is added to water, then the acid HO2 is formed, together with KOH, and the acid HO2 then quickly decomposes, giving O2, H2O and some H2O2.

j_sum1 - 20-5-2015 at 23:12

https://www.youtube.com/watch?v=c-wjagDxx68
http://en.wikipedia.org/wiki/Potassium_superoxide
http://www.sigmaaldrich.com/catalog/product/aldrich/278904

Never heard of this. Learn something new every day!
(Thanks woelen.)

jock88 - 20-5-2015 at 23:51


How's about OHO !! ;);)

j_sum1 - 21-5-2015 at 01:20

OHO OHO OHO
Oxidising Santa.

gatosgr - 21-5-2015 at 01:40

santa doesnt like this

Pyrovus - 24-5-2015 at 05:48

Quote: Originally posted by elementcollector1  
Ah, a radical. That explains it, then. And yeah, a radical is usually much more reactive than a compound.


Actually no, because the deprotonated form (superoxide) is a radical as well, so nothing is gained in terms of stability by deprotonation on that front.

I think the reason for the increased acidity of HO2 compared to H2O2 has to do with the fact that the bond order of the O-O bond in H2O2 is 1, whereas in superoxide it is 1.5. This means that p orbitals are being used up to create a pi bond between the oxygens, and as such the hybridisation of the oxygens will be that of less p character and more s character. As s orbitals are on average closer to the nucleus than p orbitals, increased s character means that the electrons will be held onto more tightly, and less available for bonding. As such, any proton bound to the oxygen will have a weaker bond and be more easily removed. This is the same phenomenon that makes alkynes stronger acids than alkenes, which are in turn stronger acids than alkanes.

DrMario - 25-5-2015 at 13:56

Quote: Originally posted by chem_haruka  
pKa(HO2)=4.88 pKa(H2O2)=11.8 pKa(HO)=11.9 pKa(H2O)=14(15.6)


Well played, sir. And thank you, because your post generated this beautiful reply, very much worth quoting:
Quote: Originally posted by Pyrovus  
Quote: Originally posted by elementcollector1  
Ah, a radical. That explains it, then. And yeah, a radical is usually much more reactive than a compound.


Actually no, because the deprotonated form (superoxide) is a radical as well, so nothing is gained in terms of stability by deprotonation on that front.

I think the reason for the increased acidity of HO2 compared to H2O2 has to do with the fact that the bond order of the O-O bond in H2O2 is 1, whereas in superoxide it is 1.5. This means that p orbitals are being used up to create a pi bond between the oxygens, and as such the hybridisation of the oxygens will be that of less p character and more s character. As s orbitals are on average closer to the nucleus than p orbitals, increased s character means that the electrons will be held onto more tightly, and less available for bonding. As such, any proton bound to the oxygen will have a weaker bond and be more easily removed. This is the same phenomenon that makes alkynes stronger acids than alkenes, which are in turn stronger acids than alkanes.