Exploring Chemical Analysis
Exploring Chemical Analysis
5th Edition
ISBN: 9781429275033
Author: Daniel C. Harris
Publisher: Macmillan Higher Education
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Chapter 9, Problem 9.17P
Interpretation Introduction

Interpretation:

Among the buffers that have highest buffer capacity at pH equals to 9 has to be determined.

Concept Introduction:

Buffers are those that resist pH change on addition of acid or base and even if it is diluted. It is formed by combination of weak acid and strong base or vice versa. Buffer capacity is defined as the quantity of acid or base added to volume of buffer  to bring change in pH.

The equation for buffer is described by Henderson-Hasselbach equation and it is a rearranged form of equilibrium constant, Ka. It relates pH of buffer solution and pKa value. It also helps to find equilibrium pH in acid-base reactions. Consider an equation of dissociation of an acid as follows:

  HAH++A

Formula to calculate pH is as follows:

  pH=pKa+log([A][HA])

Here,

pKa is acid dissociation constant of weak acid HA.

[A] is concentration of conjugate base A

[HA] is concentration of acid HA.

The maximum value of buffer capacity is attained when pH becomes equal to pKa and this can happen only if ratio of ([A][HA]) is one. At this condition there is no change in pH of solution.

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