TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 15 (2010) pp 426-429

How to Save Overshot Titrations: A Bubbly New Twist at the End of Acid Base Titrations

Myung-Hoon Kim*, Pablo Conde Pedroso, and Maureen Burkart

Science Department, Georgia Perimeter College - Dunwoody Campus, 2010 Womack Rd, Dunwoody, GA, USA 30338, Myung.Kim@gpc.edu
Received July 17, 2010. Accepted September 23, 2010.

Published: 22 December 2010

Abstract. A bubbly new modification was developed in order to make the traditional acid-base titrations in beginning chemistry laboratory more exciting and lively with additional inquiries (such as “What in your breath makes the pink go away?”) and to save overshot titration trials which could have been discarded otherwise. The method involves students exhaling air using a plastic straw into the over-titrated acid-base mixture, which turned pink-colored with phenolphthalein indicator. The pink color of the solution fades away when the excess base is neutralized. It was found that there is good correlation between the degree of over-titration and the time required to neutralize the excess NaOH with the expired air. An empirical equation, that can fit the blowing time of the air into the solution (y) vs. the excess base (x) added was determined by regression methods. Thus, the actual volume of base required for an over-titrated solution is found by subtracting the volume of NaOH overshot from the uncorrected volume. The method is simple, inexpensive, can save titration trials, makes the lab more exciting; it can be widely applied to many other types of acid base titrations.

Key Words: Laboratories and Demonstrations; general chemistry

(*) Corresponding author. (E-mail: Myung.Kim@gpc.edu)

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