Introduction

            Buffers are solutions that resist drastic change in pH upon the addition of small amounts of acid or base.    The most common buffers consist of weak acids with their conjugate bases. Buffers can combine with H+ ions or release them so they help maintain a relatively constant hydrogen concentration in many systems. They are important in regulating pH of fluids and tissues of living organisms.

            Buffer action is the resistance of the buffer solution to changes in hydrogen ion concentration. This is due to the ability of the salt component to neutralize the added acid and the acid to neutralize the added base.        The Henderson-Hasselbach equation is used to calculate the pH of a buffer solution made up of known concentrations of a  weak acid and its conjugate base or the salt. The Henderson-Hasselbach is expressed as:  pH = pKa + log([salt]/[acid]).  The concentration of the buffer is equal to the sum of the concentration of the acid and the salt.

            Buffer capacity is the number of equivalents of strong acid or base needed to change the pH by one unit per liter of h e buffer. It is directly proportional to the concentration of the components of the buffer. Maximum buffer capacity occurs when the ratio of the concentration of the salt to the acid is equal to one. When this occurs, pH = pKa.
 

Procedure

            Prepare 0.10 M buffer using 0.20 M acid and salt solutions with pH (between 2-8.2) to be given by the instructor. Calculate  volume  before preparation of the assigned buffer.
 

Buffer action
 
 

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Chemistry 145.1
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