pH and pOH Calculator
Calculate pH, pOH, [H⁺], and [OH⁻] from any one known value for aqueous solutions at 25°C.
Formulas Used
pH from [H⁺]:
pH = −log₁₀[H⁺]
pOH from [OH⁻]:
pOH = −log₁₀[OH⁻]
Relationship at 25°C (Kw = 1×10⁻¹⁴):
pH + pOH = 14
[H⁺] × [OH⁻] = Kw = 1×10⁻¹⁴ mol²/L²
Reverse calculations:
[H⁺] = 10−pH | [OH⁻] = 10−pOH
Assumptions & References
- All calculations assume aqueous solution at 25°C (298 K), where Kw = 1×10⁻¹⁴.
- The pH scale is bounded between 0 and 14 for standard dilute aqueous solutions; concentrated strong acids/bases can exceed this range.
- Activity coefficients are assumed to be 1 (ideal dilute solution); real solutions may deviate at high ionic strength.
- pH is defined as per the IUPAC recommendation: pH = −log₁₀(aH⁺), where aH⁺ is the activity of hydrogen ions.
- Reference: Atkins, P. & de Paula, J. Physical Chemistry, 10th ed.; IUPAC Gold Book — pH definition.