Toward a Greener and Safer Chemistry: Chloride Analysis in Seawater with Sustainable Indicators

There has been an increased awareness of the hazardous properties of certain chemicals in recent years, and hexavalent chromium has hazardous properties that are recognized both in the United States and in the European Union. Several compounds containing this species have traditionally been used in school chemistry laboratories, and there is a need to find alternatives. In this article, a way to perform precipitation titration of chloride in seawater without the use of potassium chromate as the indicator is presented. A microscale titration activity that uses hydrogen phosphate and thymolphthalein as indicators was developed, and the activity contains a motivation part where the students are presented with a problem, a case where they must help an oceanographer identify her mixed samples. The activity was tested not only by high school students but also with chemistry teachers as well. Feedback from students and teachers indicates that the laboratory activity is enjoyable and easy to perform and that the chemistry is in alignment with high school curricula in the Nordic countries.