Chapter 18, Problem 109A

Interpretation Introduction

Interpretation:

The chemical equation is to be written when small amount of acid or base is added to $C_2{H}_{5}N{H}_3{}^{+}/C_2{H}_{5}N{H}_2$ buffer system.

Concept introduction:

Buffer solution is a solution in which there is no change in $pH$ takes place on adding small amount of acid and base.

Answer to Problem 109A

$\begin{array}{l}Onadditionofacid:\\ C_2{H}_{5}N{H}_2+H^{+}\to C_2{H}_{5}N{H}_3{}^{+}\\ Onadditionofbase:\\ O{H}^{-}+C_2{H}_{5}N{H}_3{}^{+}\to H_{2}O+C_2{H}_{5}N{H}_2\end{array}$

Explanation of Solution

$\begin{array}{l}Onadditionofacid:\\ C_2{H}_{5}N{H}_2+H^{+}\to C_2{H}_{5}N{H}_3{}^{+}\\ Onadditionofbase:\\ O{H}^{-}+C_2{H}_{5}N{H}_3{}^{+}\to H_{2}O+C_2{H}_{5}N{H}_2\end{array}$

When acid is added, the equilibrium shifts towards left side and when base is added to buffer system, the equilibrium shifts towards right side.

Conclusion

Thus buffer system resists the change in the value of $pH$ on adding small amount of acid and base.