Am I missing something very fundamental here for phosphoric acid's second pKa value?
- I check the Wikipedia page and these are the values: (1) 2.148, (2) 7.198, (3) 12.377
- Then I check Sigma-Aldrich website and it says: (1) 2.15, (2) 6.82, (3) 12.38
Why is the second pKa value different? Any ideas?
I need to prepare potassium phosphate buffer for my proteins and got stuck with this simple problem.