pH and Acid-Base Calculator
Calculate pH, pOH, [H⁺], [OH⁻], and acid/base classification for aqueous solutions at 25°C.
dimensionless (0–14)
Results will appear here.
Formulas Used
Core relationships (at 25°C, Kw = 1×10⁻¹⁴):
- pH = −log₁₀[H⁺]
- pOH = −log₁₀[OH⁻]
- pH + pOH = 14 (at 25°C)
- [H⁺][OH⁻] = Kw = 1×10⁻¹⁴ mol²/L²
Weak acid (exact quadratic):
- HA ⇌ H⁺ + A⁻ → Ka = [H⁺]²/(C − [H⁺])
- [H⁺] = (−Ka + √(Ka² + 4·Ka·C)) / 2
Weak base (exact quadratic):
- B + H₂O ⇌ BH⁺ + OH⁻ → Kb = [OH⁻]²/(C − [OH⁻])
- [OH⁻] = (−Kb + √(Kb² + 4·Kb·C)) / 2
Assumptions & References
- All calculations assume dilute aqueous solutions at 25°C (298.15 K).
- Kw = 1.0×10⁻¹⁴ mol²/L² at 25°C; this value changes with temperature.
- Activity coefficients are assumed to be 1 (ideal dilute solution); real solutions may deviate.
- The weak acid/base model uses the exact quadratic formula, not the 5% approximation, ensuring accuracy at all concentrations.
- pH scale of 0–14 applies to dilute aqueous solutions; concentrated solutions can have negative pH or pH > 14.
- References: Atkins & de Paula, Physical Chemistry, 10th ed.; Zumdahl, Chemistry, 9th ed.; IUPAC recommendations for pH (2002).