Calculated and Measured Forms of Chlorine in Bleach at Different pH Values, A Coupled Equilibrium Experiment

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 17 (2012) pp 112-117
DOI 10.1007/s00897122426a

Calculated and Measured Forms of Chlorine in Bleach at Different pH Values, A Coupled Equilibrium Experiment

Andrew Lunning, Jordan Whitworth, Josh Grandquist, Alan Nicholson, and Michael K. Bellamy*

Department of Chemistry, 800 University Drive, Northwest Missouri State University, Maryville, MO 64468, mbellamy@embarqmail.com
Received April 27, 2012. Accepted May 19, 2012.

Published: 15 June 2012

Abstract. An experiment is presented that uses commercial bleach to teach the concept of coupled equilibrium. The predicted concentrations of five forms of chlorine in a solution of commercial bleach are calculated as a function of pH using a spreadsheet. Students then prepare diluted bleach solutions and adjust the pH of the solutions to values ranging from about 1 to 12. Students learn how changing the pH shifts the series of coupled chemical reactions. Students then measure the concentrations of three of the forms of chlorine, Cl₂, HClO, and ClO^- at different pH values by ultraviolet (UV) spectrophotometry. Since the UV spectra of the different forms of chlorine overlap, a spreadsheet is used to perform a least squares calculation to quantify the different forms of chlorine.

Key Words: Laboratories and Demonstrations; analytical chemistry; coupled equilibrium; ultraviolet spectrophotometry; computer modeling

(*) Corresponding author. (E-mail: mbellamy@embarqmail.com)

Article in PDF format (351 KB) HTML format

Supporting Materials:

Notes for instructors, student exercises, sample spreadsheet to solve the set of coupled equilibrium and sample spreadsheet to perform least-squares calculation are available (980 KB).