Exploring Emission and Absorption Spectroscopy in the First-Year General Chemistry Laboratory

Abstract

In the first-year general chemistry laboratory course, instrumental data collection involving sample quantification has often been limited to absorption spectroscopy due to the inaccessibility of emission techniques suitable for large enrollments and novice users. In this laboratory experiment, students explore the complementary techniques of emission and absorption spectroscopy, in which sample quantification respectively occurs via the measurement of light emitted or absorbed by the sample. Calibration curves are constructed for both techniques. Eschewing atomic absorption spectroscopy (AAS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES), instrumentation not typically available for large general chemistry courses, quantitative data is instead collected using a series of carefully implemented flame tests. Students perform flame tests on alkali, alkaline earth, and transition metal compounds using the emitted light to gain a thorough understanding of emission spectroscopy. In Week 1, students are introduced to emission spectroscopy through the identification of unknown components in air, lamps, and contaminated soil samples. In Week 2, students carry out quantitative emission and absorption characterization of Na and Cu solutions, comparing the two techniques through experimental observations and analyzed results. Calibration curves with high linear regressions (r2 > 0.992) are prepared and used to determine the concentrations of provided reference samples, with averaged student data resulting in reasonably low percent errors (<12% for Na emission, <11% for Cu emission, and <2% for Cu absorption) when compared to the known concentrations. Students then compare experimental flame emission results to provided ICP data to gain experience with a sensitive, quantitative emission technique.