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5.4 ACID VALUE

 ​            The acid value is the number of mg of potassium hydroxide required to neutralize the free acid in 1 g of the substance, when determined by the following method, unless otherwise stated in the monograph.

Procedure

 ​            Place about 10 g of the substance, accurately weighed, or the quantity specified in the monograph, in a 250-ml flask, and add 50 ml of a mixture of equal volumes of ethanol and ether which has been neutralized after the addition of 1 ml of dilute phenolphthalein TS. If necessary, heat with caution until the substance is completely dissolved; titrate with 0.1 M potassium hydroxide VS, shaking constantly until a pink colour which persists for 15 seconds is obtained. Calculate the acid value from the equation:

where 56.11 = the molecular weight of potassium hydroxide,

 ​            V = the volume, in ml, of 0.1 M potassium hydroxide VS,

 ​            M = the exact molarity of the potassium hydroxide, and

 ​            W = the weight, in g, of the test substance.