   Chapter 15, Problem 2ALQ

Chapter
Section
Textbook Problem

# A friend asks the following: “Consider a buffered solution made up of the weak acid HA and its salt NaA. If a strong base like NaOH is added, the HA reacts with the OH− to form A−. Thus the amount of acid (HA) is decreased, and the amount of base (A−) is increased. Analogously, adding HCI to the buffered solution forms more of the acid (HA) by reacting with the base (A−). Thus how can we claim that a buffered solution resists changes in the pH of the solution?” How would you explain buffering to this friend?

Interpretation Introduction

Interpretation:

An explanation regarding the concept of the buffering of a solution on basis of the given buffer solution is to be stated.

Concept introduction:

A solution that resists a change in the pH on addition of an acid or an alkali is termed as a buffer solution.

To determine: An explanation regarding the concept of the buffering of a solution on basis of the given buffer solution.

Explanation

Explanation

• The addition of a strong base to a buffer solution decreases the concentration of the weak acid present. Hence, the value of the pH does not change
• Given

The buffer solution is made up of a weak acid HA and its salt NaA .

The pH of a solution is calculated by the Henderson-Hassel Balch equation,

pH=pKa+log[salt][acid]

The addition of a strong base to a buffer solution decreases the concentration of the weak acid and increases the concentration of the salt.

Therefore, the ratio [salt][acid] is not much affected. Hence, the value of the pH does not change

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