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  Home > JCE Print > Journal of Chemical Education > Issues > 1999  > October  >
In the Laboratory
Ascorbic Acid as a Standard for Iodometric Titrations: An Analytical Experiment for General Chemistry
Cesar R. Silva, Jose A. Simoni, Carol H. Collins, and Pedro L. O. Volpe
Institute of Chemistry, Unicamp, P. O. Box 6154, 13083-970 Campinas, São Paulo, Brazil
Cover
October 1999
Vol. 76 No. 10
p. 1421
Abstract
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.

See Letter re: this article.
More Information
*  Citation
 Silva, Cesar R.; Simoni, Jose A.; Collins, Carol H.; Volpe, Pedro L. O. J. Chem. Educ. 1999 76 1421.
*  Keywords
 Laboratory Instruction; Redox Reactions; Quantitative Analysis; Analytical Chemistry
*  History
 Created:
Last Updated:		 September 6, 1999
June 23, 2005
Link to Letter added (April 2004).
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