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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 16 (2011) pp 160-163

Analysis of Household Products: Coulometric Titration Experiment in the Undergraduate Laboratory

Rajeev B Dabke*, Zewdu Gebeyehu, Mary Petermann, Napoleon Johnson, Jr., and Krutik Patel

Department of Chemistry, Columbus State University, Columbus, GA 31907,
Received August 25, 2010. Accepted March 25, 2011.

Published: 18 June 2011

Abstract. Experiments for coulometric analysis of two commercial household products are presented. The experiments are intended for an undergraduate laboratory course. The quantitative analysis of acetic acid in vinegar and calcium carbonate in antacid tablets is reported. Faraday’s laws of electrolysis were applied to quantify the active ingredient present in these household products. A recipe for constructing a coulometry cell made of polydimethylsiloxane (PDMS) polymer is presented. Platinum wires served as anode and cathode. A known amount of current was passed through the cell and the charge was monitored. Acetic acid in vinegar was titrated against OH(aq) ions generated in the cathode compartment. The progress of the coulometric titration for the analysis of vinegar was monitored by measuring the pH and by detecting the end point using a phenolphthalein indicator. The coulometric back titration method was used for the analysis of calcium carbonate in antacid tablets. The calcium carbonate was completely dissolved in excess acid generated by the coulometric method. The remaining acid was back titrated against the coulometrically generated OH-(aq) ions. Bromothymol blue was used as an indicator. The amount of acid neutralized by calcium carbonate was determined from the difference in the anodic and cathodic charge. The experimental results obtained by coulometric titration and volumetric titration were in good agreement with each other. The experiments highlight the real world significance of Faraday’s laws of electrolysis.

Key Words: Laboratories and Demonstrations; quantitative analysis; electrochemistry; household products

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