There is a formula linking the values of pH and pOH which allows determining the pH or pOH based on one another.

It is derived from the expression of water ionization, *K*w **= **[H^{+}][OH^{–}].

To get the pH and pOH correlation, we take a negative log of both sides of the equation:

-log [H^{+}] + (- log [OH^{–}]) = – log 10^{-14}

^{ }

Notice that the terms on the left represent the pH and pOH of the solution (-log [H^{+}] = pH, – log [OH^{–}] = pOH). Therefore, we can write that:

pH + pOH = 14

Let’s see how this can be used to calculate, for example, the pH from pOH.

**For example**, determine the pH of a 0.850 *M* NaOH.

The strategy here is to calculate the pOH and then, using the **pH + pOH = 14** relationship, determine the pH.

NaOH is a strong base, so [OH^{–}] = [NaOH], and therefore, the pOH is:

pOH = -log 0.850 = 0.0706

The pH then is equal to:

pH = 14 – pOH = 14 – 0.0706 = 13.9

As expected, the pH is very high because it is a solution of a strong base.

**Check Also**

- Definitions of Acids and Bases
- Acid-Base Reactions
- Acid-Base Titrations
- Conjugate Acid and Conjugate Base
- Autoionization of Water and
*K*_{w} - The pH and Acidity
- Acid Strength,
*K*_{a}, and p*K*_{a} - Base Strength,
*K*_{b}and p*K*_{b} *K*_{a}, p*K*_{a},*K*_{b}, and p*K*_{b}Relationship- The pH of a Strong Acid and Base
- The pH of a Weak Acid
- The pH of a Weak Base
- ThepH of Polyprotic Acids
- The acidity of a Salt Solution
- The pH of a Salt Solution
- The pH of Salts With Acidic Cations and Basic Anions
**Acids and Bases Practice Problems**

why some time

log k =+14

log k=-14

log k = 0