11A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It has the property that the pH of the solution changes very little when a small amount of acid or base is added to it. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications.
When hydrogen ions are added to the solution the equilibrium moves to the left, in accordance with Le Chatelier's principle, as there are hydrogen ions on the right-hand side of the equilibrium expression. When hydroxide ions are added the equilibrium moves to the right as hydrogen ions are removed in the reaction H+ + OH- → H2O. Thus, some of the added reagent is consumed in shifting the equilibrium and the pH changes by less than it would do if the solution were not buffered.
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