pH Calculator — Calculate pH from Hydrogen Ion Concentration
pH is a measure of the acidity or basicity of an aqueous solution. It is defined as the negative base-10 logarithm of the hydrogen ion concentration. This calculator converts a given [H+] concentration in molar units (M) to pH instantly.
Use this tool to quickly estimate the pH of solutions in laboratory preparations, titrations, environmental sampling, and when working with buffer systems.
How pH is Calculated
The mathematical relationship is straightforward:
pH = -log10([H+])Where [H+] is the hydrogen ion concentration in moles per liter (M). For example, a 1 × 10^-7 M solution of hydrogen ions corresponds to pH 7, which is neutral at 25°C.
Examples
Example 1: [H+] = 1e-3 M
pH = -log10(1e-3) = 3.00 (acidic)
Example 2: [H+] = 1e-7 M
pH = -log10(1e-7) = 7.00 (neutral at 25°C)
Example 3: [H+] = 1e-9 M
pH = -log10(1e-9) = 9.00 (basic)
Practical Notes
- pH is temperature-dependent for some solutions; this calculator assumes standard behavior at typical laboratory temperatures (around 25°C).
- Extremely low concentrations approaching 0 are not physically meaningful for pH calculation; the tool requires a positive concentration.
- For very dilute solutions (e.g., < 1e-8 M), ionic water autoionization can affect the effective pH and more advanced corrections may be needed.
FAQs
What if I enter 0 or a negative concentration?
The pH is undefined for zero or negative hydrogen ion concentrations. Enter a positive concentration value to compute pH.
Can I convert pH to [H+]?
Yes — you can convert pH to [H+] using [H+] = 10^-pH. This calculator performs the inverse operation (from [H+] to pH).
Is pH the same as acidity?
pH is a numeric scale that quantifies the acidity or basicity of a solution. Lower pH values indicate higher acidity (higher [H+]), while higher pH values indicate more basic solutions (lower [H+]).
References & Further Reading
Recommended textbooks and resources: general chemistry textbooks for acid-base chemistry, analytical chemistry texts for pH measurement and buffer calculations, and peer-reviewed articles on activity corrections in very dilute solutions.