What is the difference in buffering capacity between a buffer comprising 0.1mol/L acetic acid and 0.1mol/L acetate, and a sample of distilled water?

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To know the difference in the buffer capacity of the two liquids, we have to know their pH's.

Distilled water:

pH = 7.00 

Acetic acid - acetate buffer:

We shall use the Henderson-Hasselbalch Equation:

`pH = -log K_a + log ([Sal t]/[Acid])`


`pH = -log K_a + log ([acet ate]/[acetic acid])`


`pH = pK_a + log ([acet ate]/[acetic acid])`

  • pK_a_acetic acid = 4.76
  • [acetate] = [acetic acid] = 0.1 mol/L

`pH = 4.76 + log ([0.1]/[0.1])`

pH = 4.76

So it is pH 7.00 versus pH 4.76 and the difference would be pH 2.24. This only means that the acetic acid buffer has more buffer capacity than that of distilled water. Upon the addition of strong acid or strong base, the acetic acid - acetate buffer will tend to prevent dramatic change of pH whereas distilled water will show great change of pH.

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