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The pH Calculator converts hydrogen ion concentration to pH and provides the corresponding pOH and hydroxide ion concentration. The pH scale is a logarithmic measure of acidity that ranges from 0 (strongly acidic) to 14 (strongly basic) in aqueous solutions at 25 degrees Celsius.
Enter the hydrogen ion concentration in moles per liter and the calculator instantly returns the pH, pOH, and hydroxide concentration. This tool is essential for chemistry students, laboratory researchers, and anyone working with acid-base chemistry.
The pH is defined as the negative base-10 logarithm of the hydrogen ion concentration:
pH = -log10([H⁺])
The relationship between pH and pOH in water at 25 degrees Celsius is:
pH + pOH = 14
The hydroxide ion concentration is calculated from the pOH:
[OH⁻] = 10^(-pOH)
These relationships arise from the autoionization of water, where Kw = [H⁺][OH⁻] = 1.0 x 10⁻¹⁴ at 25 degrees Celsius.
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A 0.001 M HCl solution has a pH of 3.0, which is moderately acidic. The hydroxide concentration is 10⁻¹¹ M.
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A solution with [H⁺] = 3.2 x 10⁻⁶ M has a pH of approximately 5.49, which is mildly acidic, similar to black coffee.
pH measures the concentration of hydrogen ions (H⁺) in a solution on a logarithmic scale. A pH of 7 is neutral (pure water at 25 degrees Celsius), values below 7 are acidic, and values above 7 are basic (alkaline). Each pH unit represents a tenfold change in hydrogen ion concentration.
The pH scale is logarithmic because hydrogen ion concentrations in practical solutions span many orders of magnitude, from about 10 M (concentrated strong acid) to 10⁻¹⁵ M (concentrated strong base). A logarithmic scale compresses this enormous range into a convenient 0-14 scale that is easier to work with and compare.
Yes. Concentrated strong acids can have pH values below 0 (for example, 10 M HCl has pH approximately -1), and concentrated strong bases can have pH values above 14. The 0-14 range applies to typical aqueous solutions where hydrogen ion concentrations are between 1 M and 10⁻¹⁴ M.
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