The added 10 cm3 of 0.1 mol dm 3 NaOH (equivalent to 0.002 mol) combines with 0.001 mol of acetic acid to produce 0.001 mol of sodium acetate. Reapplying equation (3.83) using the revised salt and acid concentrations gives

The pH of the buffer has been increased by only 0.06 units following the addition of the alkali.

Buffer capacity

The effectiveness of a buffer in reducing changes in pH is expressed as the buffer capacity, fi. The buffer capacity is defined by the ratio dc fi (3.85)

where dc is the number of moles of alkali (or

EXAMPLE 3.11 Calculation of buffer capacity

Calculate the buffer capacity of the acetic acid-acetate buffer of Example 3.9 at pH 4.0.

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