At 25 °C, the sum of pH and pOH for any aqueous solution is equal to __________.

### Why this is right For aqueous solutions at 25 °C, pH and pOH add to 14. If one value is known, the other can be found by subtracting it from 14. ### The concept The relationship follows from water’s ion-product constant at this temperature. It changes with temperature, so the stated temperature matters. ### Terms - **pOH**: the negative base-ten logarithm of hydroxide-ion concentration. - **Ion-product constant of water**: the equilibrium relationship between hydrogen and hydroxide ions in water. ### Remember At 25 °C, use $pOH = 14 - pH$.