andra - 20-4-2012 at 01:21
pH calculation
I want to make a buffer with a pH=7.2. How do I calculate how NaHCO3 and HEPES I must add??
- NaHCO3 (6.216mM; pKa 6.1)
- Hepes (12.5mM; pKa 7.3)
Mercurius - 20-4-2012 at 02:13
The Henderson-Hasselbach Equation:
pH = pKa + log ([Base]/[Acid])
pH - pKa = log ([Base]/[Acid])
10^(pH-pKa) = ([Base]/[Acid])
Then use this molar ratio to calculate the respective volumes.
andra - 20-4-2012 at 04:09
Thank you Mercurius!
But what are the reactions?
NaHCO3 -- Na+ HCO3-
and for Hepes??
and what are the equations for the concentrations??
I have done this a lot of times for CH3COOH and NaOH etc. but I am confused with this HEPES
Mercurius - 20-4-2012 at 06:47
HEPES buffer is zwitterionic, so theres a sulfonic acid that can donate a proton to solution and tertiary amine that can accept a proton. So you'll
need to work out which species are in solution based upon the pH, and then you can make some simplifying assumptions to work out the activities from
the equilibrium equations. I'll leave this to you, but here's a good resource to get you started.
hhttp://www.chembuddy.com/?left=pH-calculation&right=toc