pH Calculator
Choose what you know, enter the concentration in mol/L and get pH, pOH, [H+] and [OH-] at 25 C, where Kw = 1.0 × 10^-14.
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Formula
pH = -log10[H+]pOH = -log10[OH-]pH + pOH = 14at 25 C, becauseKw = [H+][OH-] = 1.0 × 10^-14- Strong acid or base:
[H+](or[OH-]) = concentration × ions released per formula unit
Worked example
[H+] = 0.001 mol/L: pH = -log10(0.001) = 3. Then pOH = 14 - 3 = 11 and [OH-] = 1.0 × 10^-11 mol/L.
A 0.05 mol/L strong acid releasing 2 H+: [H+] = 0.1 mol/L, so pH = 1.
Frequently asked questions
How do you calculate pH?
pH = -log10[H+], with [H+] in mol/L. For [H+] = 1.0 × 10^-3 mol/L, pH = 3.
How do you find pH from [OH-]?
First pOH = -log10[OH-], then pH = 14 - pOH at 25 C. For [OH-] = 0.01 mol/L, pOH = 2 and pH = 12.
What is the pH of a strong acid or base?
A strong acid dissociates completely, so [H+] equals its concentration times the H+ it releases. 0.05 mol/L of an acid releasing 2 H+ gives [H+] = 0.1 mol/L and pH 1. A strong base works the same way through pOH.
Why does this use 14?
At 25 C the ion product of water is Kw = 1.0 × 10^-14, so pH + pOH = 14. At other temperatures Kw changes, and so does the neutral pH. Very dilute solutions below about 10^-6 mol/L are also affected by the water itself, which this simple model ignores.