Bath & Target The carbonate system being set

Bath Volume L

Target pH

Buffer pKa

Bicarbonate to carbonate step is 10.33 at 25 deg C

Soda Ash Dose g/L

Soda Ash Purity %

Salt Dose g/L

Acid Load & Water What tries to pull the pH down

Acid Released by Dye Hydrolysis meq

Substrate Acid Demand meq/kg

Fabric Charge kg

Allowable pH Drop

Water Alkalinity as CaCO3 mg/L

Soda Ash to Charge

— kg

At the stated dose, corrected for purity

Buffer Chemistry & the Overshoot

Buffering Over What Is Needed: — x
Actual pH Drop from the Acid Load: —
Alkali Present as Carbonate: — %
Carbonate to Bicarbonate Ratio: — x
Buffer Capacity: — meq/L per pH
Total Acid Load: — meq
Alkalinity the Water Brings: — meq
Salt to Charge: — kg

The pKa of 10.33 is the second dissociation of carbonic acid at 25 deg C and shifts with temperature and ionic strength - at dyeing temperature and 60 g/L of salt the effective value is lower, which moves the carbonate fraction up. The buffer capacity expression treats the carbonate system in isolation and ignores the contribution of the substrate, of any sequestrant, and of the hydroxide term itself, which becomes significant above pH 12. Salt is reported as a charge only; its role in reducing the electrical barrier to dye uptake is not modelled here. The acid released by hydrolysis is an input rather than a prediction, since it depends on the dye class, the shade depth and how much dye hydrolyses rather than fixes.

Reactive Dyeing Salt, Alkali & Carbonate Buffer Capacity — free, with the formula and a worked example, at Textile School.