pH calculator
pH is minus the base-10 logarithm of the hydrogen ion concentration in mol/L. The logarithm is computed to 45 digits, not with a float.
mol/L
pH
3.000
- pOH
- 11.000
- Hydroxide concentration
- 1e-11 mol/L
Show the working
- Hydrogen ion concentration = 0.001
- pH = -log10(0.001) = 3
- pOH = 14 - 3 = 11
- Hydroxide concentration = 1e-14 / 0.001 = 1e-11
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- pH = -log10[H+]
- pOH = 14 - pH at 25 degrees Celsius
- [H+] x [OH-] = 1.0 x 10^-14 at 25 degrees Celsius
The water ion product Kw is 1.0 x 10^-14 only at 25 degrees Celsius. At 60 degrees neutral water sits nearer pH 6.5, which is still neutral because [H+] still equals [OH-].
Strictly pH is defined on activity rather than concentration; the two diverge in concentrated solutions.