Chapter 16.3, Problem 16.4WE

Interpretation Introduction

Interpretation:

The concentration of hydroxide ions in stomach acid at ${\text{25}}^{\circ }\text{C}$ has to be calculated.

Concept Information:

Autoionization of water:

Water, a weak electrolyte, ionizes to small extent as follows,

${\text{H2O}}_{\text{(l)}}\rightleftarrows {\text{H}}^{\text{+}}{}_{\text{(aq)}}{\text{ + OH}}^{\text{-}}{}_{\text{(aq)}}$

The reaction is known as autoionization of water.

The equation of equilibrium for autoionization of water is,

${\text{K}}_{\text{w}}\text{=}{\text{[H}}^{\text{+}}{\text{][OH}}^{\text{-}}\text{]}$

Where,

${\text{K}}_{\text{w}}$ is ion-product constant of water

${\text{[H}}^{\text{+}}\text{]}$ is concentration of hydrogen ion

${\text{[OH}}^{\text{-}}\text{]}$ is concentration of hydroxide ion

The equilibrium expression for water at $\text{25}{}^{\text{o}}\text{C}$ is, ${\text{[H}}^{\text{+}}{\text{][OH}}^{\text{-}}\text{]= 1}\times {\text{10}}^{\text{-14}}$

Therefore,

  $\begin{array}{l}{\text{K}}_{\text{w}}\text{=}{\text{[H}}^{\text{+}}{\text{][OH}}^{\text{-}}\text{]}\\ \text{=1}\times {\text{10}}^{\text{-14}}\end{array}$

To Calculate: The concentration of hydroxide ions in stomach acid at ${\text{25}}^{\circ }\text{C}$