pOH Calculator

pOH measures the hydroxide ion concentration in a solution — the higher the pOH, the more acidic the solution, and the lower the pOH, the more alkaline it is. Select whether you have an [OH⁻] Hydroxide Ion Concentration, a pH value, or an [H⁺] Hydrogen Ion Concentration, then enter your value into the pOH Calculator to get the pOH value. Secondary outputs include the corresponding pH, OH⁻ concentration, H⁺ concentration, and solution type (acidic, neutral, or alkaline).

mol/L

Enter hydroxide ion concentration in mol/L

Enter pH value (0-14 scale)

mol/L

Enter hydrogen ion concentration in mol/L

Results

pOH Value

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pH Value

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OH⁻ Concentration

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H⁺ Concentration

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Solution Type

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Frequently Asked Questions

What is pOH and how does it relate to pH?

pOH is the negative logarithm of hydroxide ion concentration [OH⁻]. It measures the basicity of a solution. pH and pOH are related by the equation: pH + pOH = 14 (at 25°C). When pH is low (acidic), pOH is high, and vice versa.

How do you calculate pOH from hydroxide ion concentration?

Use the formula: pOH = -log([OH⁻]), where [OH⁻] is the hydroxide ion concentration in mol/L. For example, if [OH⁻] = 0.001 mol/L, then pOH = -log(0.001) = 3.

What is the pOH scale range?

The pOH scale ranges from 0 to 14, similar to the pH scale. A pOH of 7 is neutral, values less than 7 indicate basic solutions, and values greater than 7 indicate acidic solutions. Note that this is opposite to the pH scale.

How can I find pOH if I only know the pH value?

Simply use the relationship: pOH = 14 - pH (at 25°C). For example, if pH = 9, then pOH = 14 - 9 = 5. This relationship is based on the water dissociation constant Kw = 1.0 × 10⁻¹⁴.

What does it mean when pOH is less than 7?

When pOH < 7, the solution is basic (alkaline). This means there are more hydroxide ions (OH⁻) than hydrogen ions (H⁺) in the solution. The lower the pOH value, the more basic the solution.

Can pOH be negative or greater than 14?

In very concentrated solutions, pOH can theoretically be negative (very basic) or greater than 14 (very acidic), but these extreme values are rare in typical aqueous solutions and indicate highly concentrated acids or bases.

Why is the relationship pH + pOH = 14 important?

This relationship comes from the water dissociation constant (Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25°C). It allows you to easily convert between pH and pOH values and is fundamental to understanding acid-base chemistry.

How do I convert between ion concentrations and pOH?

To go from [OH⁻] to pOH: pOH = -log([OH⁻]). To go from pOH to [OH⁻]: [OH⁻] = 10^(-pOH). Similarly, you can use [H⁺] = 10^(-pH) and the relationship [H⁺][OH⁻] = 1.0 × 10⁻¹⁴ to find any missing value.