What is the pH from Concentration Calculator?
This tool converts between the hydrogen ion concentration of an aqueous solution and its pH. pH is a logarithmic measure of acidity: low values mean acidic, 7 is neutral at 25 °C, and high values mean basic (alkaline). Enter a concentration to get the pH, or enter a pH to recover the concentration. The calculator also reports pOH and the hydroxide ion concentration.
How to use it
Choose a mode. In Concentration → pH, type the hydrogen ion concentration [H+] in moles per litre (for example 0.0001 or 1e-4). In pH → Concentration, type a pH value (typically 0–14). The result panel shows the pH, the matching [H+], the pOH, and the [OH-]. Concentration must be a positive number for a valid pH.
The formula explained
The core relationship is $$\text{pH} = -\log_{10}\!\left( \text{[H}^+\text{] (mol/L)} \right)$$ where [H+] is in mol/L. Inverting it gives $$\left[\text{H}^+\right] = 10^{-\text{pH}}$$ Because water self-ionises, \(\text{pH} + \text{pOH} = 14\) at 25 °C, so \(\text{pOH} = 14 - \text{pH}\) and \(\left[\text{OH}^-\right] = 10^{-\text{pOH}}\). The logarithmic scale means each whole pH unit is a tenfold change in concentration.
Worked example
Suppose [H+] = 0.0001 mol/L (\(1 \times 10^{-4}\)). Then $$\text{pH} = -\log_{10}(0.0001) = -(-4) = 4$$ The solution is acidic. The pOH is \(14 - 4 = 10\), and \(\left[\text{OH}^-\right] = 10^{-10} = 0.0000000001\) mol/L.
FAQ
Can pH be negative or above 14? Yes. Very concentrated strong acids can give a pH below 0, and very concentrated bases above 14. The scale is just a logarithm, not a hard limit.
Why does the neutral point equal 7? At 25 °C pure water has \([\text{H}^+] = 10^{-7}\) mol/L, giving pH 7. At other temperatures the neutral pH shifts slightly.
What units does concentration use? Moles per litre (molarity, mol/L). Scientific notation like 1e-3 is accepted.
