Calculadora de pH
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
pH = −log[H⁺] ; pOH = 14 − pH
About this calculator
The pH Calculator is an online tool that calculates the pH and pOH of a solution from the hydrogen ion concentration ([H⁺]) provided by the user. pH is a measure of the acidity or basicity of an aqueous solution, defined as the negative logarithm (base 10) of the H⁺ concentration. At 25 °C, the relationship between pH and pOH is pH + pOH = 14, allowing both values to be obtained from a single input.
How it works: the user enters the H⁺ concentration in mol/L (molarity). The calculator applies the formula pH = −log₁₀([H⁺]) and then calculates pOH by subtracting pH from 14. The result is displayed with two decimal places, indicating whether the solution is acidic (pH < 7), neutral (pH = 7), or basic (pH > 7). This tool is useful for chemistry students, lab professionals, and anyone needing quick pH determination.
When to use? In lab experiments, quality control of products (e.g., food, cosmetics), water treatment, pools, aquariums, and agriculture (soil). For instance, when preparing a buffer solution, pH calculation is essential for effectiveness. It also helps in chemistry classes to verify theoretical or practical exercises.
Important considerations: the formula assumes a temperature of 25 °C. At other temperatures, the ion product of water (Kw) changes, and the pH + pOH = 14 relationship no longer holds. Also, the calculator is accurate only for dilute (low concentration) and ideal solutions. For highly concentrated strong acids or bases, activity effects may shift the actual pH. Always use the correct unit (mol/L) and ensure the entered concentration is free H⁺, not total acid concentration.
Frequently asked questions
What does pH mean?
pH stands for potential of hydrogen, a scale measuring the acidity or basicity of an aqueous solution, ranging from 0 to 14 (though it can be lower or higher in extreme cases).
How do I convert H⁺ concentration to pH?
Use the formula pH = −log₁₀([H⁺]), where [H⁺] is in mol/L. Simply enter the concentration into the calculator to get the pH.
Does the calculator work at any temperature?
No. The relationship pH + pOH = 14 is valid only at 25 °C. At other temperatures, the ion product of water changes, altering the pOH calculation.
Can I use this calculator for concentrated strong acids?
With caution. For very concentrated solutions, ionic activity may differ from concentration, causing deviations. The calculator is most accurate for dilute solutions.
What if the calculated pH is negative?
Negative pH is possible for very acidic solutions with [H⁺] > 1 mol/L. The calculator handles it normally, but keep in mind that extreme values may have practical limitations.