Chapter U4.19, Problem 8E

Interpretation Introduction

Interpretation:

The pH of a 0.256 M NaOH solution needs to be calculated.

Concept Introduction:

The acidity of a solution is expressed in terms of its pH which is essentially the measure of the hydrogen ion (H⁺) concentration of that solution. Mathematically,

  ${\text{pH = -log[H}}^{\text{+}}\text{] -----(1)}$

If the pH is below 7 the solution is termed as acidic, if greater than 7 the solution is basic. A neutral solution will have a pH = 7

The pH and pOH are related by the following equation:

  $\text{pH + pOH = 14 -----(2)}$

Where:

  $\text{pOH = }-{\text{log[OH}}^{-}\text{] -----(3)}$

  $$

Answer to Problem 8E

13.4.

Explanation of Solution

The concentration of NaOH = 0.256 M

Since NaOH is a strong base, the OH- concentration is 0.256 M

The pOH of the solution can be calculated as follows:

  $\begin{array}{l}\text{pOH = }-{\text{log[OH}}^{-}\text{]}\\ \text{=}-\text{log[}0.256\text{] = 0}\text{.59}\end{array}$

The pH of the solution can be calculated as follows:

  $\begin{array}{l}\text{pH = 14}-\text{ pOH }\\ \text{= 14}\text{.0 }-0.59=13.4\end{array}$

Conclusion

Thus, the pH of 0.256 M NaOH solution is 13.4.