๐งช pH Converter
Calculated assuming an aqueous solution at 25ยฐC, where pH + pOH = 14.
Enter a pH value or hydrogen ion concentration [H+] (mol/L) to convert between them using the basic chemistry formula pH = -log10[H+], along with pOH and hydroxide ion concentration [OH-].
How to use
- Choose whether to calculate from pH or from concentration.
- Enter the value.
- pH, pOH, [H+], and [OH-] are calculated automatically.
How the calculation works
pH measures the concentration of hydrogen ions (Hโบ) in a water-based solution and is defined as: pH = โlogโโ[Hโบ] [Hโบ] is the molar concentration of hydrogen ions (mol/L). Because the scale is logarithmic, each drop of 1 in pH means ten times the hydrogen ion concentration, and a drop of 2 means a hundred times. This tool computes [Hโบ] from pH as 10^(โpH), and pH from [Hโบ] as โlogโโ[Hโบ]. In water, the product of the Hโบ and hydroxide ion (OHโป) concentrations is constant (1 ร 10โปยนโด at 25ยฐC), so pH and pOH (= โlogโโ[OHโป]) satisfy pH + pOH = 14. The tool uses this to show pOH and [OHโป] as well.
Worked example
pH 3 [Hโบ] = 10โปยณ = 0.001 mol/L pOH = 14 โ 3 = 11 [OHโป] = 10โปยนยน mol/L [Hโบ] = 3.2 ร 10โปโต mol/L pH = โlogโโ(3.2 ร 10โปโต) โ 4.49 Typical pH values Lemon juice: about 2, coffee: about 5, pure water: 7, seawater: about 8.1, soapy water: about 10
Things to be aware of
- pH + pOH = 14 holds at 25ยฐC. The ionic product of water changes with temperature; pure water at 60ยฐC has a pH of about 6.5 and is still neutral.
- The calculation does not distinguish concentration from activity (the effective concentration that takes part in reactions), so concentrated solutions can differ from measured values.
- Very strong acids and bases can have a pH below 0 or above 14, and the tool will calculate those too.
FAQ
What formula is used for pH?
pH = -log10[H+], the negative base-10 logarithm of the hydrogen ion concentration [H+] (mol/L).
What is pOH?
A similar value derived from the hydroxide ion concentration [OH-]. In an aqueous solution at 25ยฐC, pH + pOH = 14.
Why is pH 7 considered neutral?
In pure water at 25ยฐC, [H+] = [OH-] = 1ร10โปโท mol/L, giving pH = pOH = 7. A pH below 7 is acidic, and above 7 is alkaline (basic).