Buffered solutions are used when the pH of a solution needs to stay constant. Th

Question

Buffered solutions are used when the pH of a solution needs to stay constant. The pH of a buffered solution will change slightly when an incoming acid or incoming base is added, but there will not be drastic changes to the pH of the buffered solution. Why does the pH of the buffered solution only change a little bit when an incoming acid or base is added? Buffered solutions are used when the pH of a solution needs to stay constant. The pH of a buffered solution will change slightly when an incoming acid or incoming base is added, but there will not be drastic changes to the pH of the buffered solution. Why does the pH of the buffered solution only change a little bit when an incoming acid or base is added? Why does the pH of the buffered solution only change a little bit when an incoming acid or base is added?

Explanation / Answer

Buffer solutions achieve their resistance to pH change because of the presence of an equilibrium between the acid HA and its conjugate base A?.

HA ? H+ + A?
When some strong acid is added to an equilibrium mixture of the weak acid and its conjugate base, the equilibrium is shifted to the left, in accordance with Le Châtelier's principle. Because of this, the hydrogen ion concentration increases by less than the amount expected for the quantity of strong acid added. Similarly, if strong alkali is added to the mixture the hydrogen ion concentration decreases by less than the amount expected for the quantity of alkali added.
Buffers work by reacting with any added acid or base to control the pH. For example, let's consider the action of a buffer composed of the weak base ammonia, NH3, and its conjugate acid, NH4+. When HCl is added to that buffer, the NH3 "soaks up" the acid's proton to become NH4+. Because that proton is locked up in the ammonium ion, it proton does not serve to significantly increase the pH of the solution. When NaOH is added to the same buffer, the ammonium ion donates a proton to the base to become ammonia and water. Here the buffer also serves to neutralize the base.

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