Solved: Over time, as their free fatty acid (FFA) content increases, edible fats and
Chapter 4, Problem 4.131(choose chapter or problem)
Over time, as their free fatty acid (FFA) content increases, edible fats and oils become rancid. To measure rancidity, the fat or oil is dissolved in ethanol, and any FFApresent is titrated with KOH dissolved in ethanol. In a series of tests on olive oil, a stock solution of 0.050 M ethanolic KOH was prepared at 25_C, stored at 0_C, and then placed in a 100-mL buret to titrate any oleic acid [CH3(CH2)7CH CH(CH2)7COOH] present in the oil. Each of four 10.00-g samples of oil took several minutes to titrate: the first required 19.60 mL, the second 19.80 mL, and the third and fourth 20.00 mL of the ethanolic KOH. (a) What is the apparent acidity of each sample, in terms of mass % of oleic acid? (Note: As the ethanolic KOH warms in the buret, its volume increases by a factor of 0.00104/_C.) (b) Is the variation in acidity a random or systematic error? Explain. (c) What is the actual acidity? How would you demonstrate this?
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