Connect solution acidity and basicity through water’s ion product.
Difficulty
Beginner
Read time
3 min
Prerequisites
Basic algebra and molar quantities
Source
OpenStax, Chemistry 2e, §14.2Adapted from Teng-Jui Lin’s CHEM 155 equation sheet. The linked textbook reference was used to check the equation and its physical context. Pending editorial review.
Adapted from Teng-Jui Lin, Equation Sheets, under CC BY 4.0.
FormuLab combined the water ion-product relation with the logarithmic pH and pOH definitions, generalized the 25 °C sum to temperature-dependent pK_w, and added variables, assumptions, and an original worked example.
The sum of pH and pOH equals pK_w when both use a consistent activity convention. The commonly used value 14.00 applies to water near 25 °C and should not be assumed at every temperature.
| Symbol | Meaning | Units |
|---|---|---|
| Negative base-10 logarithm of hydronium activity | ||
| Negative base-10 logarithm of hydroxide activity | ||
| Negative base-10 logarithm of the water ion-product constant |
Find pH from pOH at a stated temperature.
Avoid treating the value 14 as temperature-independent.
At 25 °C, take pK_w = 14.00. Find the pH of a solution whose pOH is 3.00.
Adapted from Teng-Jui Lin’s CHEM 155 equation sheet. The linked textbook reference was used to check the equation and its physical context. Pending editorial review.
Adapted from Teng-Jui Lin, Equation Sheets, under CC BY 4.0.
FormuLab combined the water ion-product relation with the logarithmic pH and pOH definitions, generalized the 25 °C sum to temperature-dependent pK_w, and added variables, assumptions, and an original worked example.
Assumptions
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