About pH Calculator
pH measures how acidic or basic a solution is: pH = −log10 of the hydrogen ion concentration in mol/L. For a hydroxide concentration the calculator finds pOH = −log10[OH⁻] and then pH = 14 − pOH, which holds at 25 °C. Below 7 is acidic, 7 is neutral, and above 7 is basic. It expects the ion concentration itself, so for weak acids or bases first work out how much has dissociated.
How to use pH Calculator
- Fill in "Concentration" and "Ion".
- The result appears below and updates as you type.
- Copy the result with the copy button, or download it as a file where that is offered.
Questions about pH Calculator
What is the pH of a 0.001 mol/L solution of a strong acid?
A strong acid releases all its hydrogen ions, so the hydrogen ion concentration is 0.001 mol/L and pH = −log10(0.001) = 3. Each tenfold dilution raises the pH by one unit.
Why do pH and pOH add up to 14?
In water at 25 °C the product of the hydrogen and hydroxide ion concentrations is always 1 × 10⁻¹⁴. Taking the negative logarithm of both sides gives pH + pOH = 14.
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