Journal of Chemical Education最新文献

In this three-component laboratory module, upper-division chemistry students were introduced to the kinetics of the aspirin hydrolysis reaction and determined the concentration of its active pharmaceutical ingredient (acetylsalicylic acid-ASA) using a modern, benchtop ultraviolet-visible (UV-vis) absorption spectrophotometer. In the first component, students prepared analyte solutions from over-the-counter aspirin tablets and a relevant number of standards (n = 9-10) through both serial and parallel dilutions. In the second component, the ASA concentrations of three over-the-counter formulations (325 mg per tablet) were determined with percent differences as small as 1.1% using the Beer-Lambert law and external calibration curves. In the third component, students evaluated the reaction order (pseudo-first order), the rate constant (e.g., k = 3.0 × 10^-4 s^-1 at 75 °C), and the activation energy (E _a ∼ 67.3 kJ mol^-1) of the hydrolysis reaction of ASA at various temperatures (e.g., 25, 37, 50, 75, and 85 °C). The last component was completed using a student-centered instructional approach, namely, process-oriented guided-inquiry learning (POGIL), which helped refine students' research process skills and both basic and in-depth laboratory skills (weighing, solution handling, micropipetting, operation of a pH meter and a modern, benchtop absorption spectrophotometer). The student and instructor evaluations indicated a positive learning experience and high interest in this laboratory that was inspired by the quality control and quality assurance of pharmaceutical drugs.

In this three-component laboratory module, upper-division chemistry students were introduced to the kinetics of the aspirin hydrolysis reaction and determined the concentration of its active pharmaceutical ingredient (acetylsalicylic acid-ASA) using a modern, benchtop ultraviolet–visible (UV–vis) absorption spectrophotometer. In the first component, students prepared analyte solutions from over-the-counter aspirin tablets and a relevant number of standards (n = 9–10) through both serial and parallel dilutions. In the second component, the ASA concentrations of three over-the-counter formulations (325 mg per tablet) were determined with percent differences as small as 1.1% using the Beer–Lambert law and external calibration curves. In the third component, students evaluated the reaction order (pseudo-first order), the rate constant (e.g., k = 3.0 × 10^–4 s^–1 at 75 °C), and the activation energy (E_a ∼ 67.3 kJ mol^–1) of the hydrolysis reaction of ASA at various temperatures (e.g., 25, 37, 50, 75, and 85 °C). The last component was completed using a student-centered instructional approach, namely, process-oriented guided-inquiry learning (POGIL), which helped refine students’ research process skills and both basic and in-depth laboratory skills (weighing, solution handling, micropipetting, operation of a pH meter and a modern, benchtop absorption spectrophotometer). The student and instructor evaluations indicated a positive learning experience and high interest in this laboratory that was inspired by the quality control and quality assurance of pharmaceutical drugs.

In this second-semester exploratory lab experiment, undergraduate students are introduced to the more than a century-old reductive pinacol coupling reaction of aldehydes and ketones as a powerful carbon–carbon bond forming reaction. Students learn that this reaction is often mediated by an active electron donor metal, such as Na, Mg, or Al, which produces a radical anion known as a ketyl that dimerizes via a carbon–carbon bond to yield a 1,2-diol (also known as a vicinal diol). Students perform this reaction on benzaldehyde using Al-KOH in an aqueous medium as a “green” route to the vicinal diol 1,2-diphenylethane-1,2-diol (also known as hydrobenzoin), which exists in meso- and dl-diastereomeric forms. These diols are widely used as ligands, chiral auxiliaries, and synthetic intermediates and have received particular attention owing to their diverse applications. Students then use ¹H NMR spectral analysis to experimentally establish the diastereoselectivity (dl:meso ratio) associated with this reaction by obtaining the ¹H NMR spectrum of their product and comparing it with the NMR spectra of authentic meso-hydrobenzoin and authentic dl-hydrobenzoin. Specifically, they analyze the NMR spectra of individual samples of their pinacol coupling product spiked with authentic meso-hydrobenzoin as well as authentic dl-hydrobenzoin and benzyl alcohol (the latter being a possible byproduct) and look for changes in the intensity of the benzylic proton resonances that appear in the NMR spectra.

Climate change is disrupting the Earth and endangering all of its life. It is vital that our students learn about its causes in order to be better prepared to help adapt to and mitigate the consequences. As chemistry (and other science) teachers, we have a special responsibility to provide students in our classrooms with basic science concepts that help them understand climate science and why the climate is changing. Fortunately, climate science concepts are the same as those included in many of our courses, so adding connections to the climate does not require wholesale changes to what we already teach. Many of us find that hands-on activities are an effective way to introduce and/or reinforce conceptual learning, and these activities often make excellent connections to the climate. To promote this approach, the Wisconsin Initiative for Science Literacy has produced a free, online Climate Science Activities Workbook that provides several examples of familiar activities that can be used this way. One of these is outlined here to provide a flavor of what is available in the Workbook.

Tomatoes are one of the main sources of carotenoids in the human diet, being responsible for important health-promoting benefits. Nowadays, a growing interest in making chemistry more environmentally friendly has been replacing some dangerous chemicals with daily-life materials. Accordingly, a greener protocol to teach chromatography, colorimetry, solubility, and some alkene reactions using tomato paste was developed. An innovative method was developed to efficiently extract the major tomato pigments, lycopene and carotenes, using accessible and low-toxicity organic solvents in the presence of a biodegradable dehydrating agent. Paper chromatography, using an eco-friendly eluent, allowed an easy and reliable separation of lycopene from the other carotenes, emerging as a simple and efficient technique for its detection. Then, a simple protocol enabled selective separation of the yellow carotenoids, cis-lycopene and (all)trans-lycopene by a “supermarket” column chromatography on potato starch eluted in a reversed-phase mode with low-toxicity eluents. Finally, reactions of carotenoids with common electrophiles were performed and easily monitored by the naked-eye through color alterations, demonstrating not only the presence of double bonds but also the principles of colorimetry and the mechanisms underlaying their health-promoting properties. Thus, a colorful, simple, sustainable, affordable, and extremely appealing activity was developed that is useful to illustrate the principles of solubility, solid–liquid extraction, chromatography, colorimetry, and addition reactions to double bonds, which may be implemented in first year practical classes of chemistry and biochemistry degrees. Moreover, this activity is well suited to motivate students’ learning through connections with daily-life chemistry, bringing chemistry closer to the real world.

We describe the measurement of the specific surface area of silica gel via solution adsorption method using paper-based microscale laboratory. The students utilized microfluidic paper-based analytical devices, plotted a calibration graph, and quantified the methylene blue content after adsorption by silica gel. This experiment has the advantages of low cost, fast speed, easy operation, and environmental friendliness compared to using a UV–visible spectrophotometer to determine the specific surface area. A total of 108 students majoring in chemical education participated in this practice in the sixth semester, and all students completed the experiment within 3 h. Of the total number of students participating, 85.2% of participants obtained a specific surface value with a relative error < 30%, and 94.4% of them obtained a calibration curve with a determination coefficient > 0.96. The study demonstrates the feasibility of adopting this modified laboratory experiment in physical chemistry teaching laboratories. The students′ responses to a questionnaire and their experimental reports indicated a high degree of student satisfaction, interest, and skill development after performing this experiment.

Teaching the three-dimensional structure of saccharides has consistently been a challenging aspect of organic chemistry courses, impeding students’ ability to grasp more advanced topics in biochemistry and food chemistry. In this article, we designed and developed a novel d-glucopyranose model using 3D printing technology for the first time. This model can be adapted into other glucose-like monosaccharides through simple painting techniques. Notably, the model can also be utilized for the assembly of various saccharides, including maltose, cellobiose, amylose, amylopectin, glycogen, cyclodextrin, cellulose, chitin, chitosan, and heparin. It serves as an intuitive and movable tool to visualize glycosidic bond types and molecular shapes of saccharide. Hands-on activities have demonstrated that these glucose models could significantly enhance students’ comprehension of the three-dimensional structure of saccharides, thereby reinforcing their comprehension of the physical and chemical properties and functions of these macromolecules. The modular assembly method significantly reduces the volume of the models and simplifies the operation compared with the ball and stick model. Furthermore, these models are compact and reusable, making them highly practical for educational use.

In this Communication we describe the use of nondeuterated solvent NMR spectroscopy experiments in large enrollment organic chemistry teaching laboratories. We use deuterated solvent free NMR spectroscopic analysis of several base promoted alkyl halide substitution and elimination reactions, which are taught ubiquitously in undergraduate organic chemistry, to demonstrate its utility and reliability for large enrollment classes. When such NMR experiments are used to track reaction progress and mechanism, they are found to be extremely useful and reliable, keeping waste generated in the laboratories and the price of experiments low, all while eliminating the need for deuterated halogenated NMR solvents.

Nuclear magnetic resonance spectroscopy, infrared spectroscopy, and mass spectrometry are widely utilized techniques for structural identification and verification. They play a crucial role in the education of chemists and students of related scientific disciplines. Assessments often hinge on the students’ ability to deduce the structure of an unknown compound or confirm its identity from a given set of spectra. This process resembles solving a spectral puzzle, wherein pieces of information must be assembled into a coherent overall structure. Despite the importance of such assessments, literature on their development is rare. In this contribution, we present our approach: A five-step process exemplified by the Summer 2023 exam and further illustrated by a retrospective of past exams. We provide guidance for the selection of target compounds and share our experience gained over the years, including the incorporation of specific subtasks aimed at breaking up the process of structural elucidation into smaller steps and enhancing the objectivity of partial credit allocation.

A laboratory experiment has been designed for teaching laboratories aimed at training students in the basics of spectroscopy in junior and senior level undergraduate chemistry courses. Despite the ubiquity of light-based tools in modern science, students often find it difficult to comprehend light and light-matter interactions. A portable spectrometer is utilized to record the fluorescence spectra of various lasers and molecular samples in the visible range of the electromagnetic spectrum. Three different wavelength laser sources are utilized to excite the molecular samples. Students record the experimental emission spectra from the lasers as well as from the provided inorganic and organic samples, and analyze the resulting spectra for fluorescence wavelength, spectral peak widths, and intensity. These experimental results help students understand and appreciate the quantum theory of spectroscopy. Several conceptual and reasoning difficulties among students in relating the emission spectra to energy levels of atoms and molecules are reduced by these laboratory activities and exercises. Furthermore, these laboratory exercises may stimulate research interest in students as they look forward in their careers. Although this experiment is designed for typical laboratory settings, it can be utilized in other laboratories or in outdoor environments due to the portable nature of the instrument which contains mini lasers, a mini spectrometer, and a laptop computer.