The acid value is the number which expresses in milligrams the amount of potassium hydroxide necessary to neutralize the free acids present in 1 g of the substance.
Acid value = [5.6] n/w
Where, n = the number of ml of 0.1 M potassium hydroxide required;
w = the weight, in g, of the substance.
Method
Unless otherwise specified in the individual monograph, dissolve about 10 g of the substance under examination, accurately weighed, in 50 ml of a mixture of equal volumes of ethanol (95 percent) and ether, previously neutralized with 0.1 M potassium hydroxide to phenolphthalein solution. If the sample does not dissolve in the cold solvent, connect the flask with a reflux condenser and warm slowly, with frequent shaking, until the sample dissolves. Add 1 ml of phenolphthalein solution and titrate with 0.1 M potassium hydroxide until the solution remains faintly pink after shaking for 30 seconds. Calculate the acid value from the expressionAcid value = [5.6] n/w
Where, n = the number of ml of 0.1 M potassium hydroxide required;
w = the weight, in g, of the substance.
Why ethanol and diethyl ether use in acid value test
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