How this calculator works
In a back titration, excess KOH reacts with the sample and the remaining alkali is titrated with standardized HCl. The blank-minus-sample difference measures alkali consumed by the oil or fat. Divide the equivalent KOH mass by sample mass. The reference method often rounds KOH molar mass to 56.1 g/mol; this tool uses 56.1053 g/mol from IUPAC 2021 weights. It computes the reported value rather than prescribing the laboratory procedure or soap formulation.
Formula
SV = (B - S) x cHCl x M(KOH) / sample mass, with B and S in mL, c in mol/L and sample mass in g. SV is mg KOH/g.
Worked example
For B = 25 mL, S = 5 mL, c = 0.5 mol/L and mass = 2 g, SV = 280.5265 mg/g. B = 30 mL, S = 20 mL and mass = 1 g gives the same value.
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Frequently asked questions
Why subtract sample from blank?
The sample consumes some KOH, leaving less alkali for the HCl back titration.
Is HCl molarity the same as normality here?
For this one-proton neutralization, one mole HCl supplies one equivalent.
Can blank equal sample?
The forward calculation then gives zero alkali consumption. A positive inverse value requires a positive difference.