3
11
0
M
3
11
0
M
The pOH Calculator converts hydroxide ion concentration to pOH and provides the corresponding pH and hydrogen ion concentration. While pH measures acidity, pOH measures basicity. Together they describe the complete acid-base character of an aqueous solution.
Enter the hydroxide ion concentration in moles per liter to obtain the pOH, pH, and hydrogen ion concentration. This calculator is particularly useful when working with basic solutions where the hydroxide concentration is the known quantity.
The pOH is defined as the negative base-10 logarithm of the hydroxide ion concentration:
pOH = -log10([OH⁻])
At 25 degrees Celsius, the relationship between pH and pOH is:
pH + pOH = 14
Therefore pH = 14 - pOH, and the hydrogen ion concentration is:
[H⁺] = 10^(-pH)
These relationships derive from the water autoionization constant Kw = 1.0 x 10⁻¹⁴ at 25 degrees Celsius.
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Results
A 0.001 M NaOH solution has pOH = 3 and pH = 11, making it a moderately basic solution.
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Results
A solution with [OH⁻] = 5.6 x 10⁻⁶ M has pOH of about 5.25 and pH of about 8.75, mildly basic like baking soda solution.
pH measures the concentration of hydrogen ions (H⁺) and indicates acidity, while pOH measures the concentration of hydroxide ions (OH⁻) and indicates basicity. In aqueous solutions at 25 degrees Celsius, they are related by pH + pOH = 14. A low pH (high pOH) indicates an acidic solution, while a high pH (low pOH) indicates a basic solution.
This relationship comes from the autoionization of water: H2O dissociates into H⁺ and OH⁻ with an equilibrium constant Kw = [H⁺][OH⁻] = 1.0 x 10⁻¹⁴ at 25 degrees Celsius. Taking the negative logarithm of both sides gives pH + pOH = pKw = 14. Note that at temperatures other than 25 degrees, Kw changes and the sum is no longer exactly 14.
Use pOH when you directly know the hydroxide ion concentration, which is common when working with strong bases like NaOH or KOH. It is also useful in problems involving the basicity of ammonia, amines, or other weak bases where the equilibrium expression yields [OH⁻] directly.
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