Hydroxide Ion Calculator
Calculate hydroxide ion concentration from pH or pOH.
About Hydroxide Ion Calculator
The ion product of water changes with temperature, so neutral pH is 7.0 only at 25 °C — at 50 °C it is about 6.6. Accounting for that shift matters in any warm process stream. Assuming pH 7 is neutral at all temperatures misclassifies hot solutions as acidic when they are genuinely neutral.
Formula
Hydroxide Ion
[OH⁻] = 10^(−pOH), with pOH = pK_w − pH and pK_w varying with temperature
- K_w
- Ion product of water, 10⁻¹⁴ at 25 °C but temperature dependent
Worked example
With the default values below, Hydroxide Ion Calculator returns Hydroxide Ion Concentration of 0.000984294368. Change any input above and every figure here is recalculated in your browser.
Inputs used
- pHaccepts -2–16
- 11
- Temperatureaccepts 0–100 C
- 25 C
- Solution volumeminimum 0 L
- 1 L
Results
- Hydroxide Ion Concentration
- 0.000984294368 mol/L
- pOH
- 3.0069
- Hydrogen Ion Concentration
- 0.00000000001000 mol/L
- Moles of Hydroxide in the Volume
- 0.000984294368 mol
- pH of Neutral Water at That Temperature
- 7.003
Step by step
- 1Values used
- 2Hydroxide Ion
- 3Hydroxide Ion Concentration= 0.000984294368 mol/L
- 4pOH= 3.0069
- 5Hydrogen Ion Concentration= 0.00000000001000 mol/L
- 6Moles of Hydroxide in the Volume= 0.000984294368 mol
- 7pH of Neutral Water at That Temperature= 7.003
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 14 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Hydroxide Ion calculated?
[OH⁻] = 10^(−pOH), with pOH = pK_w − pH and pK_w varying with temperature The ion product of water changes with temperature, so neutral pH is 7.0 only at 25 °C — at 50 °C it is about 6.6. Accounting for that shift matters in any warm process stream.
Why does Hydroxide Ion matter?
Assuming pH 7 is neutral at all temperatures misclassifies hot solutions as acidic when they are genuinely neutral.
What values do I need to enter?
This calculator takes 3 inputs: pH, Temperature, Solution volume. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.