In analytical chemistry, the hydroxyl value is defined as the number of milligrams of potassium hydroxide (KOH) required to neutralize the acetic acid taken up on acetylation of one gram of a chemical substance that contains free hydroxyl groups.
The acid value (AV) of the substance, determined in a separate experiment, enters into this equation as a correction factor in the calculation of the hydroxyl value (HV): Where HV is the hydroxyl value; VB is the amount (ml) potassium hydroxide solution required for the titration of the blank; Vacet is the amount (ml) of potassium hydroxide solution required for the titration of the acetylated sample; Wacet is the weight of the sample (in grams) used for acetylation; N is the normality of the titrant; 56.1 is the molecular weight of potassium hydroxide (g/mol); AV is a separately determined acid value of the chemical substance.
The content of free hydroxyl groups in a substance can also be determined by methods other than acetylation.
[1] Determinations of hydroxyl content by other methods may instead be expressed as a weight percentage (wt.
[2] The chemical substance may be a fat, oil, natural or synthetic ester, or other polyol.