pH Calculator
Calculate pH, pOH, Henderson-Hasselbalch & buffer solutions
pH from [H⁺]
pOH from [OH⁻]
Henderson-Hasselbalch
Buffer Solutions
📏 pH Scale
0 (Acidic)
7 (Neutral)
14 (Basic)
📐 Key pH Formulas
pH = -log₁₀[H⁺]
pOH = -log₁₀[OH⁻]
pH + pOH = 14 (at 25°C)
[H⁺] = 10^(-pH)
Henderson-Hasselbalch: pH = pKa + log([A⁻]/[HA])
Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴
Quick Guide
Understanding pH
pH measures acidity/basicity on a 0-14 scale. pH 7 is neutral, below 7 is acidic, above 7 is basic.
pH and pOH Relationship
At 25°C: pH + pOH = 14. This comes from Kw = 10⁻¹⁴.
Henderson-Hasselbalch
pH = pKa + log([A⁻]/[HA]). Used for buffer calculations.
Buffer Solutions
Work best when pH is within ±1 of pKa. Mix weak acid with its conjugate base.
FAQ
How to calculate pH from [H⁺]?
Use pH = -log₁₀[H⁺]. For [H⁺] = 10⁻³ M, pH = 3.
What is Henderson-Hasselbalch used for?
Calculating buffer pH, designing buffers, understanding titration curves.
Why does pH + pOH = 14?
From Kw = [H⁺][OH⁻] = 10⁻¹⁴ at 25°C. Taking -log gives pKw = 14.
How to make a buffer?
Choose acid with pKa near target pH. Use Henderson-Hasselbalch for ratio.
Is this pH calculator free?
Yes, completely free with no limitations.