March 28, 2024, 03:32:24 PM
Forum Rules: Read This Before Posting


Topic: pKa of Sulfuric Acid  (Read 7613 times)

0 Members and 1 Guest are viewing this topic.

Offline azmanam

  • Chemist
  • Sr. Member
  • *
  • Posts: 1417
  • Mole Snacks: +160/-24
  • Mediocrity is a handrail -Charles Louis d'Secondat
pKa of Sulfuric Acid
« on: August 31, 2011, 01:57:12 PM »
I've got two organic chemistry texts in front of me.  One Appendix of pKa values lists the pKa of H2SO4 as -9.  The other lists it at -3.

What gives?  Is it pKa in DMSO vs water or gas phase or something?  Neither appendix gives solvent or other conditions...  Evans lists it at -3 (2nd deprotonation at 1.99), and I can't seem to find it on Bordwell's table.

When you think sulfuric acid, what pKa value pops into your head?
Knowing why you got a question wrong is better than knowing that you got a question right.

Offline opsomath

  • Chemist
  • Full Member
  • *
  • Posts: 472
  • Mole Snacks: +50/-8
Re: pKa of Sulfuric Acid
« Reply #1 on: August 31, 2011, 02:18:39 PM »
Well I tend to think of it as having a pKa of "Yes."

I do think of it as actually being a stronger acid than HCl, which is not correct according to pKa tables; however, you use it in conditions where you need a very strong acid for forcing conditions, like in the double diazotization of a phenylenediamine.

Anyway, the consistent internet answer including Evans is -3, but if it were -9 that would be consistent with my experience of it having more punch than HCl (-8) in difficult reactions.

Online Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27634
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: pKa of Sulfuric Acid
« Reply #2 on: August 31, 2011, 03:32:40 PM »
Never seen -9 before.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Sponsored Links