Lawrence Joseph Henderson (1878–1942) was an American physician, biochemist and physiologist, to name only a few of his many pursuits. Lawrence Joseph Henderson and Karl Albert Hasselbalch A change of 1 pH unit occurs when the acetic acid concentration is reduced to 11% of the acetate ion concentration. Figure 14.17 shows how pH changes for an acetic acid-acetate ion buffer as base is added. A buffer solution has generally lost its usefulness when one component of the buffer pair is less than about 10% of the other. A good buffer mixture should have about equal concentrations of both of its components.There are two useful rules of thumb for selecting buffer mixtures: The first solution has more buffer capacity because it contains more acetic acid and acetate ion. For example, 1 L of a solution that is 1.0 M in acetic acid and 1.0 M in sodium acetate has a greater buffer capacity than 1 L of a solution that is 0.10 M in acetic acid and 0.10 M in sodium acetate even though both solutions have the same pH. Buffer capacity depends on the amounts of the weak acid and its conjugate base that are in a buffer mixture. The buffer capacity is the amount of acid or base that can be added to a given volume of a buffer solution before the pH changes significantly, usually by one unit. (credit: modification of work by Mark Ott) However, a large amount of acid exhausts the buffering capacity of the solution and the pH changes dramatically (beaker on the right). For example, strong base added to this solution will neutralize hydronium ion, causing the acetic acid ionization equilibrium to shift to the right and generate additional amounts of the weak conjugate base (acetate ion):įigure 14.16 The indicator color (methyl orange) shows that a small amount of acid added to a buffered solution of pH 8 (beaker on the left) has little affect on the buffered system (middle beaker).

The presence of a weak conjugate acid-base pair in the solution imparts the ability to neutralize modest amounts of added strong acid or base.

To illustrate the function of a buffer solution, consider a mixture of roughly equal amounts of acetic acid and sodium acetate. (credit: modification of work by Mark Ott) How Buffers Work (b) After the addition of 1 mL of a 0.01- M HCl solution, the buffered solution has not detectably changed its pH but the unbuffered solution has become acidic, as indicated by the change in color of the methyl orange, which turns red at a pH of about 4. Figure 14.14 (a) The unbuffered solution on the left and the buffered solution on the right have the same pH (pH 8) they are basic, showing the yellow color of the indicator methyl orange at this pH.

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