Chemistry / Unit 10 Chem 1832 worked example, 60 to 90 seconds
Calculating pH of a Strong Acid or Base Solution
The idea
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.
In practice
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.
Where people slip
Setting up an ICE table for a strong acid or base treats an essentially complete reaction as if it were an equilibrium worth solving for, wasting the one step this shortcut is built to skip entirely.
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