Buffering Effects and Buffer Solutions

Acetate is a conjugate base because it can gain a hydrogen and become acetic acid again (the reverse of Equation (5.20)). Acetic acid and acetate ion (such as from sodium acetate) would constitute a conjugate acid-base pair. 

An important example of a conjugate acid is the ammonium ion formed by the neutralization of ammonia with an acid  

In the process of a weak acid or weak base neutralization titration, a mixture of a conjugate acid-base pair exists in the reaction flask in the time period of the experiment leading up to the inflection point. For example, during the titration of acetic acid with sodium hydroxide, a mixture of acetic acid and acetate ion exists in the reaction flask prior to the inflection point. In that portion of the titration curve, the pH of the solution does not change appreciably, even upon the addition of more sodium hydroxide. Thus this solution is a buffer solution, as we defined it at the beginning of this section. 

The answer is in the expression for the ionization constant, K l or Kb, where the ratio of the conjugate acid and base concentrations is found. In the case of a weak monoprotic acid, HA, we have the following  

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