Free · Other calculators
Wine Molecular SO2 with Fixed pKa
Calculate molecular sulfur dioxide from measured free SO2 and pH using a fixed pKa of 1.8.
- Formula & worked example
- Private in your browser
- No signup
Calculator inputs
Loading calculator…
How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
Private by default
Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
With pH 2.8 and free SO₂ of 22 mg/L, the fixed-pKa model gives molecular SO₂ of 2 mg/L.
Molecular SO₂ = free SO₂ / (1 + 10^(pH − 1.8)).
Worked example
Enter these known values and leave the other values blank.
- Wine pH
- 2.8
- Free sulfur dioxide (SO₂)
- 22 mg/L
- Molecular sulfur dioxide
- 2 mg/L
Assumptions and limitations
- This is a simplified equilibrium model with pKa fixed at 1.8. Temperature, ethanol and solution chemistry can change the appropriate pKa.
- Molecular SO₂ is a part of free SO₂, not elemental sulfur or total sulfites. Use concentrations in compatible mass-per-volume units.
- The inverse needs molecular SO₂ greater than zero and less than free SO₂ to determine a finite pH. Zero concentration can determine another concentration but cannot uniquely determine pH.
- The supported pH is nonnegative; the tool does not prescribe a preservative addition or guarantee microbiological stability.
Common questions
Is this elemental sulfur?
No. It estimates molecular sulfur dioxide within the measured free SO₂.
Can I use it to select an addition?
Use measured chemistry and a qualified winemaking protocol. This calculation only describes the fixed-pKa equilibrium.
References
The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.