Applying mostly to systems with pHs between 6 and 8, this equation can be used to deduce the composition of a weak acid/weak base solution.  
This equation is used in clinical cases to determine the extent to which pH affects the blood.  It requires knowledge of the concentrations of a weak acid and its conjugate base in solution, as well as the pKa, or dissociation factor, of the acid in question.  Applying mostly to systems with pHs between 6 and 8, this equation can be used to deduce the composition of a weak acid/weak base solution.  FTP, identify this chemistry equation used for the calculation of pH of a buffer solution named after its two developers.
This equation is used in clinical cases to determine the extent to which pH affects the blood.  
Henderson-Hasselbach equation