Addition of Strong Acids or Bases to Buffers

Consider the acid-base neutralization reaction and determine its effect on [HA] and [A ]. This step is a limiting reactant stoichiometry calculation. 000 (Section 3.6 and 3.7) 

Use the calculated values of [HA] and [A ] along with to calculate [H j. This step is an equilibrium calculation and is most easily done using the Henderson-Hasselbalch equation (if the concentrations of the weak acid-base pair are very large compared to for the acid). 

Strong acid reacts with conjugate base component of buffer 

Strong base reacts with weak acid component of buffer 

A buffer is made by adding 0.300 mol CH3COOH and 0.300 mol CH3COONa to enough water to make 1.000 L of solution. The pH of the buffer is 4.74 (Sample Exercise 17.1). (a) Calculate the pH of this solution after 5.0 mL of 4.0 M NaOH(ag) solution is added, (b) For comparison, calculate the pH of a solution made by adding 5.0 mL of 4.0 M NaOH(ag) solution to 1.000 L of pure water. 

Let s now consider in a more quantitative way how a buffered solution responds to addition of a strong acid or base. In this discussion, it is important to understand that reactions between strong acids and weak bases proceed essentially to completion, as do those between strong bases and weak acids. Thus, as long as we do not exceed the buffering capacity of the buffer, we can assume that the strong acid or strong base is completely consumed by reaction with the buffer. 

To calculate how the pH of the buffer responds to the addition of a strong acid or a strong base, we follow the strategy outlined in V FIGURE 17.3  

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