pH Calculator (Acid & Base Concentration)
Convert between H⁺ concentration, OH⁻ concentration, pH and pOH.
Result
pH
3
pOH
11
[H⁺]
1.000e-3 M
[OH⁻]
1.000e-11 M
Nature
Acidic
Concept
pH is a logarithmic scale measuring hydrogen ion concentration in a solution. Because it is logarithmic, each unit change represents a 10× change in [H⁺]. Pure water at 25°C has [H⁺] = 10⁻⁷ mol/L, giving pH 7 (neutral).
Acids have pH < 7 (excess H⁺), bases have pH > 7 (excess OH⁻). Strong acids like HCl fully dissociate, so 0.01 M HCl gives pH = 2 directly. Weak acids partially dissociate, requiring Ka for accurate pH.
The pH + pOH = 14 relationship holds at 25°C because Kw = [H⁺][OH⁻] = 10⁻¹⁴. This changes with temperature — Kw increases as temperature rises, so neutral pH < 7 at higher temperatures.
Formula
pH=−log10[H+]
pOH=−log10[OH−]
Relationship=pH + pOH = 14 (at 25 °C)
[H+] × [OH−]=Kw = 10−14 (at 25 °C)
Variables
pHdimensionless- Negative log of hydrogen ion concentration.
[H⁺]mol/L- Molar concentration of hydrogen ions.
pOHdimensionless- Negative log of hydroxide concentration.
[OH⁻]mol/L- Molar concentration of hydroxide ions.
Kwmol²/L²- Ionic product of water = 10⁻¹⁴ at 25°C.