Calculating pH of a Strong Acid or Base Solution

Calculating the pH of a strong acid or base solution means taking its molarity directly as [H3O+] or [OH−], since dissociation is complete, then applying the pH or pOH definition and, if needed, the pH-pOH relationship to convert between the two scales.

A 0.0025 M HNO3 solution has [H3O+] = 0.0025 M directly, so pH = −log(0.0025) ≈ 2.60. A 0.0010 M NaOH solution has [OH−] = 0.0010 M, pOH = −log(0.0010) = 3.00, so pH = 14.00 − 3.00 = 11.00 at 25 °C.