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Molecular Sulfur Dioxide Equilibrium Estimate

Estimate molecular and free SO₂ concentrations from pH using a fixed 1.81 acid-dissociation constant.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

At pH 1.81, 40 mg/L free SO₂ gives 20 mg/L molecular SO₂ under the fixed aqueous-equilibrium approximation; a 0.8 mg/L molecular target corresponds to 1.6 mg/L free SO₂.

Molecular SO₂ = free SO₂ / (1 + 10^(pH − 1.81))

Worked example

Enter these known values and leave the other values blank.

Free SO₂
40 mg/L
Wine pH
1.81
Desired molecular SO₂
0.8 mg/L
Molecular SO₂
20 mg/L
Required free SO₂
1.6 mg/L

Assumptions and limitations

  • The fixed pKa is an aqueous approximation at 25°C. Alcohol and temperature affect the equilibrium. This computes concentrations, not an addition dose, microbial guarantee or regulatory limit.

Common questions

What does this estimate assume?

The fixed pKa is an aqueous approximation at 25°C. Alcohol and temperature affect the equilibrium. This computes concentrations, not an addition dose, microbial guarantee or regulatory limit.

How should I enter a different quantity?

Choose the displayed measurement units before entering a value. Clear the unknown field, enter compatible known values, and use the preserved inverse branches where available. One-way estimates and rounded package outputs keep their original direction.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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