How to Calculate pH of a Buffer
- 1). Write the chemical reaction for the dissociation of your buffer solution.
- 2). Determine the dissociation constant for the relevant acid or base. The dissociation constant is the ratio of dissociated ions to initial compound present at equilibrium, and is represented as Ka for an acid or Kb for a base. See Resources for lists of common dissociation constants.
- 3). Take the negative log (base 10) of your dissociation constant. If the solution is at equilibrium, this is the pH of your buffer solution. For example, hypobromous acid has a dissociation constant of 2 x 10^-9. log(2 x 10^-9) ~= -8.699, so the pH of a hypobromous acid buffer would be approximately 8.699.
Source...