How this calculation works
The pH, pOH & Ion Concentration Calculator converts hydrogen ion molarity [H⁺] into logarithmic pH, pOH, and hydroxide [OH⁻] concentrations across the complete 0-14 acid-base spectrum.
Mathematical formula and logic
pH = -log₁₀[H⁺], pOH = 14 - pH, [OH⁻] = 10^(-pOH), Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25°C.
Worked example
A solution with [H⁺] = 0.0001 mol/L (1.0 × 10⁻⁴ M) has a pH of -log₁₀(10⁻⁴) = 4.00, a pOH of 10.00, and [OH⁻] = 1.0 × 10⁻¹⁰ M (Acidic).
Calculation assumptions
- Standard aqueous temperature of 25°C where ion product constant of water Kw = 1.0 × 10⁻¹⁴.
- Ideal dilute solution activity coefficients (activity equals molar concentration).
Frequently asked questions
What does pH measure?
pH (potential of Hydrogen) is a logarithmic scale measuring the acidity or basicity of an aqueous solution based on the activity of hydrogen ions ([H⁺]).
What is the pH scale range?
The standard pH scale ranges from 0 to 14: pH < 7 is acidic (stomach acid ~1.5, coffee ~5.0), pH = 7 is neutral (pure water), and pH > 7 is basic/alkaline (bleach ~12.5).
Can pH be negative or greater than 14?
Yes, concentrated strong acids (like 12M hydrochloric acid) have negative pH values (~ -1.1), and concentrated strong bases can exceed pH 14.
Why is a pH difference of 1 equal to a 10-fold change in acidity?
Because the pH scale is logarithmic (base 10), a solution with pH 3 is 10 times more acidic than pH 4 and 100 times more acidic than pH 5.
What is pOH?
pOH measures hydroxide ion [OH⁻] concentration: pOH = -log₁₀[OH⁻]. In water at 25°C, pH + pOH always equals 14.
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