Chapter 16, Problem 45A

Interpretation Introduction

Interpretation:

The characteristics of buffer solutions are to be written.

Concept introduction:

A solution is buffer if it does not change the $pH$ value if small amount of acid or base is added to it.

Buffer solution is of two types:

• Acidic buffer
• Basic buffer

Answer to Problem 45A

The property of buffer is that it doesn’t allow the change in $pH$ if small amount of acid or base is added to it.

Explanation of Solution

  $C{H}_{3}COOH-C{H}_{3}COONa$ is an acidic buffer.

It works as:

  $\begin{array}{l}C{H}_{3}COOH\rightleftharpoons C{H}_{3}CO{O}^{-}+H^{+}\\ C{H}_{3}COONa\to C{H}_{3}CO{O}^{-}+N{a}^{+}\end{array}$

When small amount of base is added, it reacts with acetic acid and get neutralised.

When small amount of acid is added, common ion effect operates and equilibrium of acetic acid is shifted backward and thus effect of acid is neutralised.

  $N{H}_{4}OH-N{H}_{4}Cl$ is a basic buffer.

It works as:

  $\begin{array}{l}N{H}_{4}OH\rightleftharpoons N{H}_4{}^{+}+O{H}^{-}\\ N{H}_{4}Cl\to N{H}_4{}^{+}+C{l}^{-}\end{array}$

When small amount of acid is added, it reacts with ammonium hydroxide and get neutralised.

When small amount of base is added, common ion effect operates and equilibrium of ammonium hydroxide is shifted backward and thus effect of base is neutralised.

Conclusion

Thus, on addition of small electrolyte in a solution containing buffer, there is only slight change in $pH$ .