November 13, 2019, 04:18:30 PM
Forum Rules: Read This Before Posting


Topic: PKa of hydrazine  (Read 440 times)

0 Members and 1 Guest are viewing this topic.

Online rolnor

  • Chemist
  • Full Member
  • *
  • Posts: 715
  • Mole Snacks: +56/-3
PKa of hydrazine
« on: July 02, 2019, 08:49:03 AM »
Does anyone of you guys/gals have the second pKa for hydrazine? I can not find it.
FOUND IT! pKa1 is 8,0 and pKa2 is -1,0
« Last Edit: July 02, 2019, 09:29:48 AM by rolnor »

Offline AWK

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 6841
  • Mole Snacks: +489/-81
  • Gender: Male
Re: PKa of hydrazine
« Reply #1 on: July 02, 2019, 11:10:21 AM »
These are correct values

N2H4, pkb1 = 6.07 and Pkb2 = 15.05
AWK

Online rolnor

  • Chemist
  • Full Member
  • *
  • Posts: 715
  • Mole Snacks: +56/-3
Re: PKa of hydrazine
« Reply #2 on: July 02, 2019, 12:40:55 PM »
Why are my valeus incorrect? They are from German wikipedia, ref. 2 and 3.
https://de.m.wikipedia.org/wiki/Hydrazin

The pKa2 is from Handbook. pKa1 is from another source from 2003.

Offline AWK

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 6841
  • Mole Snacks: +489/-81
  • Gender: Male
Re: PKa of hydrazine
« Reply #3 on: July 02, 2019, 01:02:28 PM »
I did not say your values are incorrect. I show you only more precise pKb values for comparison.
AWK

Offline wildfyr

  • Global Moderator
  • Sr. Member
  • ***
  • Posts: 1365
  • Mole Snacks: +149/-9
Re: PKa of hydrazine
« Reply #4 on: July 03, 2019, 08:55:45 AM »
One is pKa other is pKb

Online rolnor

  • Chemist
  • Full Member
  • *
  • Posts: 715
  • Mole Snacks: +56/-3
Re: PKa of hydrazine
« Reply #5 on: July 03, 2019, 09:14:07 AM »
I dont follow, why are we diskussing pKb?

Offline Babcock_Hall

  • Chemist
  • Sr. Member
  • *
  • Posts: 3879
  • Mole Snacks: +244/-16
Re: PKa of hydrazine
« Reply #6 on: July 03, 2019, 12:03:19 PM »
The pKb values can be converted into pKa values.  I found 8.07 using Williams' pKa table.  Hinman, R.L. J. Org. Chem. 1958, 23, 1587.

Online rolnor

  • Chemist
  • Full Member
  • *
  • Posts: 715
  • Mole Snacks: +56/-3
Re: PKa of hydrazine
« Reply #7 on: July 03, 2019, 02:00:57 PM »
Is pKa 14-pKb? Its a bit surprising that the values are different, pKa is not difficult to meassure?
Here is one more reference giving pKa1 as 8.10
https://pubs.acs.org/doi/abs/10.1021/ja01577a030
Its important to get it right even if my correlation is very strong regardless if its 8.0 or 8.10 or 8.07
« Last Edit: July 03, 2019, 02:17:06 PM by rolnor »

Offline pgk

  • Chemist
  • Full Member
  • *
  • Posts: 804
  • Mole Snacks: +89/-23
Re: PKa of hydrazine
« Reply #8 on: July 03, 2019, 02:30:20 PM »
Kw = KaKb  →  Kb = Kw/Ka  →  logKb = log(Kw/Ka)  →  logKb = logKw - logKa  →  -logKb = -logKw + logKa  →  pKb = 14 - pKa  →  pKa = 14 - pKb
« Last Edit: July 03, 2019, 02:43:23 PM by pgk »

Offline pgk

  • Chemist
  • Full Member
  • *
  • Posts: 804
  • Mole Snacks: +89/-23
Re: PKa of hydrazine
« Reply #9 on: July 03, 2019, 03:14:49 PM »
Do not worry about slight variations of pKa and pKb values that figure in the literature because this is not so important.
Besides, measurement of these values for strong acids and bases, is not convenient because the Henderson-Hasselbach equation is not very accurate in this case.
In case of multibasic acids and polyamines, the Henderson-Hasselbach is not applicable at all and thus, pKa and pKb are indirectly measured by other methods, e.g. monoesterification, selective monoketimination, selective monoamidation or calculative methods, e.g. Hammet equation.
« Last Edit: July 03, 2019, 03:39:27 PM by pgk »

Sponsored Links