Introduction to pOH

The pOH of a solution is defined as:

\text{pOH} = -\text{log}_{10}[\text{OH}^-]

Acidic solutions have a pOH > 7. Alkaline solutions have a pOH < 7.

[H+], [OH] and Kw (water ionisation constant) are related:

K_{\text w} = 1.0 \times 10^{-14} = [\text H^+][\text{OH}^-]

pH and pOH are also related, as pH + pOH = 14.

Example

Q: Calculate the pH of a 0.00850 mol L^-1 NaOH solution.

NaOH is a strong base and fully dissociates in water:

[\text{OH}^-]=[\text{NaOH}] = 0.00850 \space\text{mol} \space\text L^{-1}

\text{pOH} = -\text{log}_{10}[\text{OH}^-]=-\text{log}_{10}[0.00850]=2.07

\text{pH} = 14-\text{pOH} = 14-2.07=11.93