I've prepared universal buffer solutions of Britton-Robinson within pH range 2 to 12. My question is, do all solutions at different pH have the same ionic strength?
I believe it would change at pH corresponding to pKa value of buffer constituent (Boric a, Phophoric a, AcOH, NaOH). So, to keep ionic strength constant in all solution, simply i can add 1 M KCl. which would overcome ionic strength of buffer constituent ?
I wish they taught buffers properly in chemistry text books, but they don't. All buffers work on the electroneutrality principle. This simply means that the sum of the concentrations of all the positive charges in solution must equal the sum of all the negative charges. Ionic strength is then the sum off all the charged (positive or negative) entities since they must be equal. It is possible to put all the components of a buffer into an Excel spreadsheet and solve for the pH or how much of any given component to add to get to a specific pH, no matter how many components are in the buffer (see attached example). You need to use the optional Solver plugin to make this work, but you can follow what is going on from the formulas
I've been using this spreadsheet since I created it in grad school in 1987.
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