IIT JEE , AIEEE Forum - Chemistry , Inorganic Chemistry - which is stronger acid?? (Q. already exists but no steady answer still!!!)

narulaajun

Which acid is stronger and why..plzz give precise REASONING

H3PO4 or H3PO3

joyfrancis

H₃PO₄, because it has more number of acidic hydrogens. Moreover , larger number of oxygens connected to the central atom makes it more acidic.

rishipratimm

well .....
its h3po3 which is supposed to be the stronger acid....
i am not quite sure if my explanation is universally acceptable....

u see, on drawing the structure of both the acids,we see that in phosphoric acid,there are two -OH groups attached to the central atom,while in phosphoric acid,there are three -OH groups attached to P....
in both structures,there is only 1 =O attached to P...
reasoning that acidic strength is measured in terms of h+ ions releasing tendency,the electron pull of the doubly bonded oxygen is more effective in h3po3 as it has to spread over only two-OH groups as compared to three -OH groups in phosphoric acid....

thus,h+ ion releasing tendency is more in phosphorous acid,so it is stronger...

narulaajun

i think h3po4 is stronger..coz the conj. base(or H+releasing ability) is more stable coz more electro-ve atoms pulling the -ve charge on one of the oxygens where H+ has been released

narulaajun

sry.diagram was rong for phosphorous acid

spideyunlimited

H3PO4 since in oxy-acids , more the number of oxygen atoms, more the stability of conjugate base and more the number of acidic H atoms that can be released.

narulaajun

spidey ur not correct..there no resonance coz it requires same 'n'(shell no. for resonanace to occur, oxygen and phosphorus have large gap in orbital energy for e- delocalization

ashish_banga

both r having 2 acidic hydrogens put due to presence of 2 P=O groups in H3PO4 it becomes more polar and acidic

pratikanand

ACIDITY

OXIDATION STATE OF CENTRAL ATOM...........

so H3PO4...

cheeers.....

svj29

dude i had a long debate wid many of the goiitains a few days ago about the same qsn...well here's the best answer.
H3PO3 is more acidic and it is becoa of that hydrogen which is directly attached to P. It cannot be protonated. It means that it will react less with Proton(H+) than H3PO4 as it has 3 OH which can be protonated to form H2O+.
Now we know that protons(H+) are released by acids and reaction between 2 acids is less than the reaction between an acid and a less acidic compound. Now as H3PO3 reacts less hence it is more acidic.
Hope U got it.

deadman

arey yaar acids are supposed to donate protons not accept them!!!!!

the -OH will rather lose a proton instead of accepting it to get protonated....bases are the ones who accept H+ or donate -OH

deadman

wat svj.. says is that h3po4 is accepting proton to get the -OH group protonated.....instead of losing a proton.....thats confusing!hope u got it right from the other poll u said

svj29

dude for the verification of all whatz said can check
http://www.goiit.com/posts/list/physical-chemistry-which-acid-is-stronger-37431.htm
AND PLZ RATE THE ANSWER OF TARINBANSAL AT THE LAST OF THE ABOVE URL IF ur satisfied with the answer... cz i copied the answer from there...

tarinbansal

SVJ is right(not that rate me thing)
But just read my ans there on the second page------>last post.
It was taught by Dr P Bahadur that day in his online class. And I dont think anyone wud like to challenge his explanation.

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