The Analysis of Dolomitic Marble: A Multifaceted Problem for General Chemistry Students

• A. M. Ranjika Priyadarshi Bopegedera ^[1]
  1. [1] The Evergreen State College, United States
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 99, Nº 2, 2022, págs. 964-974
• Idioma: inglés
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• Resumen

  • Marble, formed by the metamorphism of limestone, is commonly used in the construction industry and sculpting. The mineral in marble is either calcite [CaCO3] or dolomite [CaMg(CO3)2] or sometimes both. The pure white Carrara marble from Italy was made a household name by Michelangelo, the famous sculptor of the 16th century. Impurities, such as graphite, quartz, micas, iron oxides, pyrite, brucite, olivine, and tremolite, if incorporated into marble during its formation can impart interesting colors to this common rock. The chemical analysis of dolomitic marble presents a challenging, yet interesting problem for general chemistry students and is the subject of this article. This analysis was divided into four facets to provide the scaffolding general chemistry students needed to successfully tackle this problem. The project spanned the entire academic year and utilized both workshop (conducted in lectures) and laboratory components. A “chemists’ approach” and a “geologists’ approach” to the carbonate analysis enabled students to understand the chemical process of a back-titration from multiple perspectives as they worked through the data analysis in workshops. This preceded the laboratory work for the determination of carbonates in marble using a back-titration, after dolomitic marble samples were digested overnight with excess acid. The analysis of the results from the back-titration relied on the knowledge students gained in the workshops. The cations in dolomitic marble were quantified with atomic absorption spectroscopy later in the academic year. Since the laboratory analysis proved the marble sample to be quite pure (less than 5% impurities), the cation and anion analyses were combined to determine the empirical formula of dolomite. This as well as using their own data to grapple with accuracy, precision, random error, systematic error, and significant figures in this data analysis was more powerful for students than learning these concepts from a textbook. Valuable experiences and transferable skills gained from this project included learning and honing titration technique, sample preparation, spreadsheet software skills, and report writing. Students’ enthusiasm for this project was high even through the challenging analysis of large class data sets. This was because students were eager to find the solution to a real-world problem for which the answer was unknown to them as well as the instructor. Whole or part of this investigation can be ready adopted at any institution.