Chapter 19, Problem 107A

Interpretation Introduction

Interpretation : The $\text{pOH}$ of milk is to be calculated.

Concept Introduction : pOH stands for the potential of hydroxide ions. It measures the acidity or basicity of any solution. The pOH range lies between 0-14. pOH is calculated by the formula:

  $pOH=-log\left[O{H}^{-}\right]$

Answer to Problem 107A

The pOH of milk is $7.3$ .

Explanation of Solution

The pH of the milk is $\text{6}\text{.7}$ .

The formula for the concentration of hydrogen ions is given as

  $\left[{\text{H}}^{\text{+}}\right]=\text{antilog}\left(-\text{pH}\right)$

To calculate the concentration of hydrogen ions, substitute the values in above formula:

  $\begin{array}{c}\left[{\text{H}}^{\text{+}}\right]=\text{antilog}\left(-\text{pH}\right)\\ =\text{antilog}\left(-6.7\right)\\ =1.99\times {10}^{-7}\text{M}\end{array}$

Since the ion product constant is given as ${\text{K}}_{\text{w}}=\left[{\text{H}}^{+}\right]\left[{\text{OH}}^{-}\right]$ , the concentration of hydroxide ion is given as

  $\begin{array}{c}\left[{\text{OH}}^{-}\right]=\frac{{\text{K}}_{\text{w}}}{\left[{\text{H}}^{+}\right]}\\ =\frac{1\times {10}^{-14}}{1.99\times {10}^{-7}}\\ =0.50\times {10}^{-7}\end{array}$

The formula of pOH is given as

  $\begin{array}{c}pOH=-log\left[O{H}^{-}\right]\\ =-\log \left(0.50\times {10}^{-7}\right)\\ =7.3\end{array}$