I have been preparing 150 mM and 30 mM Tris Buffers (pka=8.3). Using .15 M solutions of both Tris and Tris-HCL.
Here is the information in which I have calculated theoretical pH values as well as collected experimental data.
I used (Ka or Kb)= x^2 / [concentration]-x to solve for the values in solution 1 and 5 of both the concentrated and diluted buffers. I also used Henderson-Hasselbach for solutions 2-4. For example, solution 2 in 150mM:
pH=8.3+log(.375M unprotonated/1.125 M protonated)=7.822
For the addition of .1 mL 1.25 M HCl I added and subtracted appropriately:
pH=8.3+log(.375-.125M unprotonated/1.125+.125M protonated)=7.50
I am having trouble applying these concepts to a diluted buffer solution. I calculated solution 1 for 30 mM buffers by simply changing the concentration by a factor of 5 (per the dilution factor) while using the ICE table Ka=x^2/ concentration-x.
I need some direction in being able to figure out the pH of the diluted solution and how to calculate the effect of .1 mL 1.25 M HCl addition to each of the dilute solutions.