Journal of Chemical Education最新文献

This article presents a journey through a sequence of steps designed to transform novices into experts in constructing Lewis structures. The progression begins with the decoration of central atoms, moves to the connection of central and terminal building blocks, and culminates in pattern recognition. This approach ultimately eliminates the need for counting valence electrons, simplifying the overall process. The method builds on the recent insightful work of Gerard Parkin ( J. Chem. Educ. 2023, 100 (12), 4644−4652), which focuses on foundational concepts, and Owen J. Curnow’s approach ( J. Chem. Educ. 2021, 98 (4), 1454−1457), which determines formal charges based on group numbers and bond counts. These steps bridge the gap between the basic techniques used by high school and first-year undergraduate students and the more advanced methods employed by experienced chemists. Unlike traditional methods found in General Chemistry textbooks, this approach enhances understanding of charged species and isoelectronicity, fostering a deeper connection with the periodic table. We will demonstrate and contrast this sequential journey with the “traditional” approach to solving Lewis structures, highlighting key insights that facilitate students’ smooth transition from introductory general chemistry to organic chemistry and beyond. With sufficient practice, this method leads to effective pattern recognition, enabling the identification of both central and terminal molecular building blocks, allowing for rapid and accurate completion of molecular skeletons through “local inspection”, including the addition of missing bonds, lone pairs, and formal charges. Mastery of these skills is crucial for success in advanced chemistry courses where electron counting is no longer practiced.

The ability to extract structural information from a drawing of a molecule is key to being successful in organic chemistry. One source of difficulty for novices in interpreting structures is that hydrogens bound to carbon are represented implicitly in the often-used line-angle structures. Other representations that explicitly show hydrogens, such as Kekulé structures or condensed formulae, are less efficient to draw than line-angle structures and can therefore make tasks such as proposing a mechanism prohibitively long. A new type of formula, the prime formula, is disclosed in this article as an efficient way to draw chemical structures with hydrogens being clearly represented. The number of hydrogen atoms on each carbon are represented by superscripts with ° = 0 H, ′ = 1 H, ″ = 2 H, and ‴ = 3 H. Pre-treatment and post-treatment data was collected and compared to a control group. By viewing a question in prime formula vs line-angle formula, an improvement in student performance with a significance of p_tukey = 0.008 and df = 63.3 was observed for mapping atoms of a starting material onto a product, a key skill for proposing complex arrow-pushing mechanisms. An increase in performance with a significance of p = <0.001 and df = 57.3 was obtained for determining the number of stereogenic centers in a complex molecule. Data collected also support that it is efficient to learn how to interpret and draw prime formulae.

Biofuels and biodiesels are a quickly expanding area of Green Chemistry and consist of mixtures of fatty acid methyl esters (FAMEs) commonly produced from plant sources. This across-the-curriculum laboratory experiment is designed to involve students in General, Organic, and Physical Chemistry courses working toward a common goal: the synthesis, analysis, and combustion of biodiesel fuels produced from common vegetable oils (liquid coconut, solid coconut, canola, and corn oils). Working in teams of General Chemistry and Organic Chemistry students, the General Chemistry students produced a single FAME through a Fischer Esterification to produce the FAMEs present in the biodiesel, which was analyzed by gas chromatography (GC) and infrared (IR) spectroscopy. Organic Chemistry students produced a biodiesel from an unknown 50:50 mixture of two vegetable oils and used the FAME GC data to identify the two oils present in their biodiesel; each oil chosen has a novel FAME profile to aid in this identification, and students were able to effectively identify the two oils in their biodiesel. Finally, Physical Chemistry students performed bomb calorimetry with the biodiesels to determine their energy content and correlate this to the vegetable oils identified in the mixture. The experiments, performed during the same week of the academic term, which we term as “Biofuels Week”, allow students to take part in the interdisciplinary nature of chemical research and experience the entire experiment as they progress through the Chemistry major and aim to foster community in the Chemistry Department at Knox College though a common goal: the production, analysis, and combustion of a biodiesel fuel.

The radial distribution functions of the hydrogen atom are discussed as an overview in General Chemistry courses and examined in detail in Physical Chemistry. While every relevant textbook has quality figures to aid students in grasping the underlying theory, gaps in understanding the connection between mathematical functions and orbital diagrams may be partially corrected by improved instructional tools. Presented here is an R Shiny application that dynamically calculates the associated Laguerre polynomial and the radial function for every orbital from 1s to 7i based on user input for the first four hydrogen-like atoms. Plots are then produced with gglot2 of the radial function, R_nl(r), the radial function squared, R_nl(r)², and the normalized radial distribution function, 4πr²× R_nl(r)², with the ability to change the range of r values of the three plots. The trapezoidal integration method within the pracma package is used to solve for the electron probability within a user-defined region of the third plot. The result of the integration is then included in the plot as a shaded area under the curve to clarify the significance of the distribution function. This technology report includes suggested problem sets to assist instructors in lower and upper division chemistry courses utilizing the application to enhance student outcomes in quantum chemistry.

National reform documents have historically shaped how we as a research community understand students’ perspectives regarding the nature of chemical knowledge and its production. However, while scholars have investigated various facets of undergraduate learning, research on how teaching is enacted in higher education remains under-addressed. Such documents may also be less relevant for instructors such as laboratory teaching assistants who may rely on more local resources (e.g., documents from staff meeting) for their synchronous (during class) and diachronous (out of class) teaching practices. Accordingly, this study inductively and deductively coded diachronous messages from 22 staff notes from introductory chemistry at a large, research-intensive university to determine trajectories of teacher identities. Results showed that messages about facilitating student discussion and choice are minimal, with more instructions to follow a script and tend to the laboratory itself. In addition, messages from staff notes remained consistent, offering few opportunities for laboratory teaching assistants to experiment, customize, and improvise their instructional practices. Finally, two focal identities-in-practice were presented that not only problematize the trajectories of teaching assistant development but also raise concern for what is taught in the instructional laboratory. We conclude with recommendations to provide laboratory teaching assistants with chemistry-specific teacher moves. In addition, future research should investigate how synchronous laboratory teaching aligns with diachronous preparation and clarify the roles of “laboratory teaching assistant.”

The ninhydrin and biuret reactions are used to detect amino acids and peptides. These reactions are experimentally effective, because vivid color changes are observed in short times. Accordingly, we aimed to develop an experimental teaching material that uses the biuret and ninhydrin reactions to distinguish aqueous solutions of Gly, Gly-Gly, Gly-Gly-Gly, and egg white. The optimal reaction conditions for Gly-Gly in both the ninhydrin and biuret reactions, which are essential for conducting this experiment, were investigated. Distinct color changes were observed for the four solution types, which facilitated their differentiation. Almost 80% of the first-year university students successfully distinguished the four sample types in practical lessons. Student reflections and observations generally provided favorable feedback, which indicated that this experimental teaching material effectively deepened students’ understanding of the chemical properties of amino acids and peptides.

The extractability of pure organic compounds is a ubiquitous concept in the pharmaceutical field. During this laboratory session, each student receives one vial containing an unknown compound. For this sample, they will determine its solubility in an organic solvent, in water, and then its extractability profile by three liquid–liquid extractions at different pH values followed by the evaporation of the organic phase and the quantification of the residue by gravimetric analysis. The data obtained will allow students to draw a curve representing the acid/base and the hydro- and lipophilic character of their given compound. Once the first part of the session is finished, the students who have tested the same compound share the results obtained. These pooled results will show that the sigmoidal-like curve of the lipophilic acid and its conjugate base or the lipophilic base and its conjugate acid have the same shape, although the solubility in organic solvent and water is different. Lipophilic amphoteric and neutral compounds are also tested in the same laboratory session. This exercise with pure compounds will allow students to identify the physicochemical characteristics of organic compounds and anticipate the separation of such compounds in a mixture.

The author teaches a chemistry laboratory course with many students who are not chemistry majors. To attract and hold their interest, the author has presented several brief lectures using different approaches to introduce cutting-edge chemistry topics. In a recent lecture on metal–organic frameworks (MOFs), the author developed papercraft models to illustrate their rational design, assembled structures, and properties. The papercraft models comprise cardboard imprinted with molecular structures and paper clips, so they are low-tech, inexpensive, and lightweight. Their structure is neither too vague nor too specific, which made it easy for the students to grasp the characteristics of MOFs. A questionnaire survey conducted afterward revealed that many students received the lecture favorably.

When teaching quantitative analytical chemistry to undergraduate students, the transitions from classical analytical methods to instrumental ones can be tough as most (if not all) of the visual/sensorial aspects of the analyses (solution color and volume and mass changes) are lost in the instrumental interface. We have observed that the loss of these aspects can have a significant impact on a student’s ability to understand instrumental methods. Coulometric titrations offer a seamless transition path between classical and instrumental methods, offering several parallels between them, especially if visual indicators are used for determining the titration endpoint, and could be used in undergraduate laboratories to facilitate this transition. Unfortunately, modern instrumentation used for coulometric titrations does not offer a hands-on experience for the user, widening the gap between this technique and classical methods and limiting the use to bridge both. Here, we report on the fabrication of a simple and affordable instrumentation that brings back the hands-on interface of a 1960s coulometer to a modern potentiostat/galvanostat and its application to an undergraduate teaching laboratory for the coulometric titration of ascorbic acid using iodine and starch solution as a visual indicator. Molecular absorption spectra are used to quantify the student’s increased accuracy in identifying the titration endpoint closer to the equivalency point with successive titrations, demonstrating important didactic aspects of this experimental practice and granting it a place in most chemistry undergraduate curriculums.

Paal–Knorr reactions are a classical method for synthesizing pyrroles, using 1,4-dicarbonyl compound and amine as reactants. It has the characteristics of green chemistry, as only two molecules of water are lost. In this teaching and learning experiment, 2,5-hexanedione and 4-tert-butylaniline were used to synthesize 1-(4-(tert-butyl)phenyl)-2,5-dimethyl-1H-pyrrole without solvent and catalyst. This method offers several advantages, including commercially available starting materials, mild reaction conditions, solvent- and catalyst-free, short reaction time, simple and convenient operation, good yield, and high atom economy. The experiment allows beginners to master experimental skills including recrystallization, filtration, and NMR, as well as the concept of green chemistry. Green chemistry is important for environmental protection, resource conservation, and the sustainable development of the planet. Therefore, green chemistry experimental learning is also significant for undergraduates. We introduced green chemistry to students and encouraged them to discuss green chemistry and environmental protection. To assess students’ understanding of green chemistry, they were asked to calculate the green metrics of the experiment to evaluate the sustainability of this process and answer the corresponding post-course questions. Results from a survey of students indicated an improved operation of the organic experiment and an enhanced knowledge of green chemistry.