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pH, pOH and approximate concentrations

Calculate pOH and approximate ion concentrations from pH and the assumed ionic product of water.

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01

Your inputs

The starting values are an example.

14 is the commonly used approximation at 25 °C.

Decimals: 12.5 · Thousands: 1,234.56. Follow the field instructions for lists.

02

Your result

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Your result will include the relevant values and units.

Understand the calculation

Formula and example

How it is calculated

pOH = pK_W − pH; [H⁺] ≈ 10^(−pH); [OH⁻] ≈ 10^(−pOH)

Worked example

At pH = 7 and pK_W = 14, pOH = 7 and both approximate concentrations are 10⁻⁷ mol/l.

Things to check

  • pH is defined using hydrogen-ion activity. The concentration approximation assumes a sufficiently dilute solution.
  • Neutral pH is pK_W/2 and therefore depends on temperature.