Sebacic acid (HOOC−(CH₂)₈−COOH) is a naturally occurring dicarboxylic acid that is also found as a normal urinary acid. Which procedure should be followed to determine the amount of sebacic acid present in 200 mg of an unknown sample composed primarily of sebacic acid and a small percentage of neutral impurities?

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11ecba2d_11c5_733a_a3bf_89cb7efd3d20_MD0008_00 In a titration, a measured amount of a solution with a known concentration (titrant) is added to another solution containing an unknown concentration of the compound to be measured (analyte). In acid-base titrations, an acid is titrated with a base (or vice versa). The resulting acid-base neutralization reaction produces a change in pH, which is monitored by a pH indicator that signals the equivalence point of the neutralization. The analyte must be fully dissolved before it can be measured. Sebacic acid has low solubility in water due to a high nonpolar hydrocarbon character. A base will convert the carboxylic acid groups into highly polar ionic salts with much higher aqueous solubility. Once dissolved, the carboxylate ions can then be titrated with an acid. Subtracting the number of moles of base (such as KOH) in the initial solution from the number of moles of acid (such as HCl) required to reach the equivalence point during the titration will give the number of moles of carboxylate groups from sebacic acid in the sample. (Choices A and B) Sebacic acid is a ten-carbon organic acid and will not significantly dissolve in dilute aqueous acids. Only a base will ionize the carboxylic acid groups and allow the compound to dissolve. Once dissolved, titration of the basic solution should then be performed using an acid. (Choice C) A dilute base will dissolve the sebacic acid sample, but basic solutions must be titrated with acids rather than with bases. Educational objective: Acid-base neutralization reactions can be used in titrations with an indicator to determine the concentration of an acidic (or basic) analyte. By assessing the equivalence point of the neutralization, the volume of titrant required can be correlated to the amount of an analyte present in solution. Acids or bases may also aid the solubility of nonpolar analytes by forming more soluble ionic salts.

Sebacic Acid (HOOC−(CH2)8−COOH) Is a Naturally Occurring Dicarboxylic Acid That

Sebacic Acid (HOOC−(CH₂)₈−COOH) Is a Naturally Occurring Dicarboxylic Acid That