One failure of this model occurs because it neglects shifts in equilibrium 
One failure of this model occurs because it neglects shifts in equilibrium caused by hydration in the reverse of the reaction under consideration. An amended form of this rule uses the Debye-Huckel equation to compute a dimensionless activity ratio rather than using the concentrations present in the familiar form. It is derived by applying the law of mass action to a proton-liberating reaction, then taking a logarithm. It fails for dilute substances and for strong acids and bases, but is typically applied to solutions containing an acid and conjugate base. For 10 points, name this equation that calculates a buffer's effect by setting pKa plus the logarithm of the concentration of a base over the concentration of its conjugate acid equal to the pH.
One failure of this model occurs because it neglects shifts in equilibrium caused by hydration in the reverse of the reaction under consideration.
the {Henderson-Hasselbalch} equation