Chemistry / Unit 10 Chem 1824 short lesson, about 20 seconds
pH and pOH Scales and Their Relationship
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The idea
pH is the negative base-ten log of hydrogen ion concentration, pOH the same for hydroxide, and at 25 °C the two sum to 14.
In practice
A solution with [H3O+] = 1.0 × 10⁻³ M has pH 3.00 and, at 25 °C, pOH 11.00.
Where people slip
The pH-plus-pOH-equals-14 shortcut holds only at 25 °C, inherited from Kw's own temperature dependence.
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