pH, pOH and Hydrogen Ion Concentration Calculator
Moves between the four ways of stating how acidic a solution is.
pH
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Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
pOH —
Hydrogen ion concentration — mol/L
Hydroxide ion concentration — mol/L
At 25 °C this is —
Reading this —
The formula
pH = −log₁₀[H⁺] pOH = −log₁₀[OH⁻] pH + pOH = 14 at 25 °C
The 14 comes from the ion product of water at 25 °C, which is 1.0 × 10⁻¹⁴. It changes with temperature.
What to watch out for
Each step of one pH unit is a tenfold change in hydrogen ion concentration. A weak acid releases only some of its hydrogen ions, so its [H⁺] is well below the acid’s own concentration.
Frequently Asked Questions
What is the pH of 0.001 mol/L hydrogen ions?
3.00.
How do I get hydrogen ion concentration from pH?
Raise 10 to the power of −pH. A pH of 4.5 is 3.162 × 10⁻⁵ mol/L.
Is pH 7 always neutral?
Only at 25 °C. Water’s ion product rises with temperature, so neutral water has a lower pH when it is hot.