The milligrams of KOH required to completely neutralize free acid present in 1 g of oils is known as acid value or neutralization number.
Determination of acid value
The accurately weighted quantity of oil is taken in a conical flask and 50mL neutral alcohol is added, the mixture is heated over bath using water condenser for one hour. The contents are cooled titrated with KOH solution using phenolphthalein indicator.
The acid value is calculated by-
The acid value of oil = (volume of KOH used (mL)×normality of KOH)/(weight of oil taken (g)@)
The significance of the acid value
- The acidity of oil is due to hydrolysis or oxidation of oil by atmospheric moisture leading to the formation of fatty acids.
- Lubricants oil with acid values greater than 0.1 corrode metals, form gum and sludge during operation.
