Acid Value

Acidity is frequently expressed as the Acid Value, which is the number of mg of potassium hydroxide required to neutralize the free acids in 1.0 g of the substance.

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USP 401

The acidity of fats and fixed oils in USP may be expressed as the number of mL of 0.1 N alkali required to neutralize the free acids in 10.0 g of substance.

Method II

Prepare 125 mL of a solvent mixture consisting of equal volumes of isopropyl alcohol and toluene. Before use, add 2 mL of a 1% solution of phenolphthalein in isopropyl alcohol to the 125 mL mixture and neutralize with alkali to a faint but permanent pink color. Weigh accurately the appropriate amount of well-mixed liquid sample indicate in the table below, and dissolve it in the neutralized solvent mixture. If the test specimen does not dissolve in the solvent, connect the flask with a suitable condenser and warm slowly, with frequent shaking, until the specimen dissolves. Shake vigorously while titrating with 0.1 N potassium hydroxide VS or 0.1 N sodium hydroxide VS to the first permanent of the same intensity as that of the neutralized solvent, before mixing with sample. Calculate Acid value by the formula:

56.11V X N/W

Acid Value	Sample Weight (g)
0-1	20
1-4	10
4-15	2.5
15-74.9	0.5
≥75.0	0.1