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Acid value is the mass of potassium hydroxide in milligrams that is required to neutralize one gram of chemical substance. The acid number is a measure of the number of carboxylic acid groups in a chemical compound, such as a fatty acid, or in a mixture of compounds. In a typical procedure, a known amount of sample dissolved in an organic solvent and titrated with a solution of alcoholic potassium hydroxide of known concentration using phenolphthalein as a colour indicator.
The acid number is used to quantify the acidity of a substance e.g. biodiesel. It is the quantity of base, expressed in milligrams of potassium hydroxide, that is required to neutralize the acidic constituents in 1 g of sample.
Veq is the volume of titrant consumed by the crude oil sample and 1 ml of spiking solution at the equivalent point, beq is the volume of titrant consumed by 1 ml of spiking solution at the equivalent point, and 56.1 g/mol is the molecular weight of KOH. WOil is the mass of the sample in grams.
The molar concentration of titrant is calculated as such: