Hydronium Concentration to pH Calculator
Convert H⁺ (hydronium) concentration in mol/L to pH using pH = −log[H⁺]. Distinct from pOH-to-pH conversion. For education only.
How to use this tool
- Enter [h⁺] concentration in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your ph and the full breakdown beneath it.
pH is defined as the negative base-10 logarithm of the hydrogen ion (hydronium) concentration: pH = −log₁₀[H⁺]. For example, if [H⁺] = 1×10⁻⁴ mol/L, then pH = 4.
For education only.
Formula
pH = −log10[H+]
pOH = 14 − pH
[OH−] = 10−pOH mol/L
How it works
This calculator takes the molar concentration of hydronium (H+) ions and applies the definition of pH as the negative base-10 logarithm of that concentration. The complementary pOH and hydroxide concentration are then derived using the 25 °C water autoionization relationship pH + pOH = 14.
The input must be a positive concentration in mol/L. The pH + pOH = 14 approximation holds at 25 °C; deviations occur at other temperatures. The solution is classified as acidic, neutral, or basic based on whether the resulting pH is below, equal to, or above 7.
Worked example
Worked example: pH from [H⁺] = 0.0001 mol/L
- Identify input: [H⁺] = 0.0001 mol/L = 1 × 10⁻⁴ mol/L.
- Apply the formula: pH = −log₁₀(0.0001) = −(−4) = 4.0.
- Derive pOH: pOH = 14 − 4.0 = 10.0.
- Classify: pH 4.0 < 7, so the solution is Acidic.
pH = 4.0; pOH = 10.0; Classification = Acidic
Key terms
- Hydronium ion [H⁺]
- The hydrogen ion (or hydronium H₃O⁺) in aqueous solution; its concentration determines the solution's acidity.
- pH
- Defined as −log₁₀[H⁺]; a lower value indicates a higher acid concentration and stronger acidity.
- Logarithm (log₁₀)
- The power to which 10 must be raised to equal a given number; e.g., log₁₀(0.0001) = −4.
- pOH
- Defined as −log₁₀[OH⁻]; related to pH by pH + pOH = 14 at 25 °C.
- Neutral solution
- A solution where [H⁺] = [OH⁻], giving pH = pOH = 7.0 at 25 °C.
Frequently asked questions
- What is the difference between H⁺ and H₃O⁺?
- In water, free protons (H⁺) immediately bond to water molecules to form hydronium ions (H₃O⁺). The two notations are used interchangeably in pH calculations.
- What [H⁺] corresponds to neutral water?
- At 25 °C, pure water has [H⁺] = [OH⁻] = 1×10⁻⁷ mol/L, giving pH = 7.