Ascorbic Acid as a Standard for Iodometric Titrations. An Analytical Experiment for General Chemistry

• Published in: Journal of chemical education Vol. 76; no. 10; p. 1421
• Main Authors: Silva, Cesar R, Simoni, Jose A, Collins, Carol H, Volpe, Pedro L. O
• Format: Journal Article
• Language: English
• Published: Easton Division of Chemical Education 01-10-1999; American Chemical Society
• Subjects: Acids; Ascorbic acid; Chemistry; Experiments; Iodine; Organic chemistry; Research Methodology; Science education; Titration; Vitamin C; Water; Hands-On Learning / Manipulatives; Oxidation / Reduction; Laboratory Instruction; High School / Introductory Chemistry
• ISSN: 0021-9584; 1938-1328
• DOI: 10.1021/ed076p1421

Ascorbic acid is suggested as the weighable compound for the standardization of iodine solutions in an analytical experiment in general chemistry. The experiment involves an iodometric titration in which iodine reacts with ascorbic acid, oxidizing it to dehydroascorbic acid. The redox titration endpoint is determined by the first iodine excess that is complexed with starch, giving a deep blue-violet color. The results of the titration of iodine solution using ascorbic acid as a calibration standard were compared with the results acquired by the classic method using a standardized solution of sodium thiosulfate. The standardization of the iodine solution using ascorbic acid was accurate and precise, with the advantages of saving time and avoiding mistakes due to solution preparation. The colorless ascorbic acid solution gives a very clear and sharp titration end point with starch. It was shown by thermogravimetric analysis that ascorbic acid can be dried at 393 K for 2 h without decomposition. This experiment allows general chemistry students to perform an iodometric titration during a single laboratory period, determining with precision the content of vitamin C in pharmaceutical formulations.