Chapter 18, Problem 77A

\If the concentration of ${\text{H}}^{+}$ ions in an aqueous solution decreases, what must happen to the concentration of ${\text{OH}}^{-}$ ions? Why?

Interpretation Introduction

Interpretation:

The relationship between hydrogen and hydroxyl ion concentration is to be explained.

Concept introduction:

In an aqueous solution,

$\begin{array}{l}{k}_w=\left[H^{+}\right]\times \left[O{H}^{-}\right]\\ where\\ k_{w}isionicproductofwater\end{array}$

Answer to Problem 77A

Hydroxyl ion concentration will increase if concentration of hydrogen ion is decreased.

Explanation of Solution

In an aqueous solution,

$\begin{array}{l}{k}_w=\left[H^{+}\right]\times \left[O{H}^{-}\right]\\ where\\ k_{w}isionicproductofwater\end{array}$

The value of $k_w$ remains constant at constant temperature.

Thus, on decreasing the hydrogen ion concentration, hydroxyl ion concentration will increase.

Conclusion

Hydroxyl ion concentration increases when concentration of hydrogen ion is decreased.