Latest revision as of 11:16, 15 August 2013

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^[1].

Methods

The acid value of a wax is determined by dissolving a known amount of the wax in alcohol and titrating the solution against standard alkali solution.

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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^[2].

Weigh 3 g of sample and place it in a clean 250 mL Erlenmeyer flask. Place 50 mL of solvent (isopropyl alcohol-toluene 5:4) connect the flask with a suitable condenser and warm slowly, with frequent shaking, until the sample dissolves. Remove the flask from the condenser and add 1 mL of phenolphthalein in isopropyl alcohol. Shake vigorously while titrating with 0.1 N potassium hydroxide. Register the volume of potassium hydroxide consumed.Calculate Acid value by the formula:

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Which:

56.11: is the molecular weight of potassium hydroxide

V: is the volume in mL

N: is the normality of the potassium hydroxide solution

W: is the weight, in g, of the sample taken

Referencia

1. ↑ Warth, A. H.; The Chemistry and Technology of Waxes. Reinhold Publishing Corporation. Second Edition, p. 586
2. ↑ Pharmacopedia/National Formulary. US., Vol. 1, 2009, p. 150