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The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 20 (2015) pp 280-284

Measurement of Seawater pH Comparing Spectrophotometric and Glass Electrode Methods

Alan L. Soli*

Department of Chemistry, Eckerd College, 4200 54th Avenue S., St. Petersburg, FL, 33711,
Received July 27, 2015. Accepted September 30, 2015.

Published: 14 October 2015

Abstract. The pH of natural seawater is measured spectrophotometrically and compared to that obtained with a glass electrode. The basis for the spectrophotometric method is the absorbance ratio of the acid and base forms of meta-cresol purple. As part of the procedure, students also determine the salinity of the seawater using conductivity measurements. The acidification of seawater is demonstrated by bubbling it with CO2.

Key Words: Laboratories and Demonstrations; general chemistry; marine chemistry; pH measurements; spectrophotometry, glass electrode

(*) Corresponding author. (E-mail:

Article in PDF format (155 KB) HTML format

Supporting Materials:

An Excel template for all of the calculations in this experiment and the actual student handout are supplied in the Supporting Materials. (104 KB)

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