All Titration Indicators are Not Created Equal-A Lecture Demonstration

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 5 Issue 4 (2000) pp 181-182

All Titration Indicators are Not Created Equal-A Lecture Demonstration

Reid Huefner and Thomas G. Richmond*

Department of Chemistry, University of Utah, 315 South 1400 East, RM 2020, Salt Lake City, Utah 84112-0850

Published online: 1 August 2000

Abstract. This demonstration provides a simple method for emphasizing the importance of indicator selection to determine the end point of a titration involving the common weak base household ammonia. By using phenolphthalein and methyl red as the indicators in the titration of two samples of aqueous household ammonia with hydrochloric acid, students can discover that there is a difference between the two apparent termination points. There is clearly a visible difference in the sharpness of the color changes that take place, and the presence of ammonia at the apparent phenolphthalein endpoint is also detected by olfactory means. By showing the different termination ranges on a titration curve, the students can readily see that phenolphthalein does a poor job of showing the proper termination point,; whereas methyl red shows the proper titration end point.

Key Words: Laboratories and Demonstrations;

(*) Corresponding author. (E-mail: richmond@chemistry.utah.edu)

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