Buffer Notes & Problems
If HA H+ + A- , then Ka = [H+] [A-] / [HA]…….rearranging:
[H+] = Ka ([HA] / [A-])…………taking –log of both sides:
pH = pKa – log ([acid] / [base]); the “negative” reverses the acid/base and we get:
pH = pKa + log ([base] / [acid]) Henderson-Hasselbalch equation
Calculate the pH of a solution containing 0.75 latic acid (Ka = 1.4E-4) and 0.25M sodium lactate.
Latic acid(HC3H5O3) is a common constituent of biologic systems.
A buffered solution contains 0.25M NH3 and 0.40M NH4Cl. Calculate the pH.
Calculate the pH of the solution that results when 0.10mol gaseous HCl is added to 1.0L of the
solution in the above problem.
A solution is made from 0.50M CH3NH2 and 0.70M CH3NH3Cl. Then 0.10 mol of NaOH is added
to 1.0 L of the solution. Calculate the pH. What would have been the pH if 0.10 mol of HCl had