Journal of Chemical Education最新文献

In spring 2020, the chemical education community faced an abrupt transition from in-person to online classes, which also necessitated online assessments. Building upon an existing three-semester study (F17, S19, and F19) using Rasch modeling and classical testing theory to improve in-person multiple choice exams, this study investigates the impact of online exams (F20, F21, and F22) on assessment quality and student performance in an undergraduate General Chemistry II class. The Cronbach’s alpha and fraction of very good/good questions were found to dramatically increase across the first two semesters (F17 and S19) and then largely plateaued for subsequent exams, regardless of in-person or online test administration. Through the use of linking questions (i.e., repeated questions from semester to semester) and equating procedures, the results indicated that (1) there was not an obvious or uniform increase or decrease in the exam quality or student performance when switching from in-person to online exams and (2) there was no evidence for an increased prevalence of cheating in the unproctored online exam relative to the prior in-person exams. While this data set is not sufficient to make any universal claims, this case study’s outcomes suggest that concerns about increased cheating on unproctored online exams are not inherently founded.

Herein, two simulated electrochemistry experiments, namely, the (i) electrochemical series, using an electronic half-cell module, and (ii) citrus fruit battery series are demonstrated for undergraduate chemistry students. The demonstration can be performed for in-person and remote students by connecting the electronic half-cell module to a computer. Remote students can participate in the demonstration on the Internet and interact with the instructor and other students. This experiment does not require the use of metal and metal ion solutions for the construction of citrus fruit batteries and electrochemical series. Therefore, this demonstration is environmentally green, because no chemical waste is produced at the end of the demonstration.

The reduction of nitroarenes to anilines is a key transformation with real-life context, central to the preparation of many important fine chemicals. The importance of this transformation has led to its inclusion in not only university organic chemistry courses but also preuniversity, especially in Europe. A variety of reagent combinations have been developed to achieve this reduction, each with its own merits; we report herein comparison of the most common methods and what and how this transformation is taught to students. Reviewing preuniversity syllabi and a variety of textbooks, we reveal a misalignment between what is taught and the conditions most commonly used in research. Palladium-catalyzed hydrogenation and iron/ammonium chloride are the most popular reaction choices in the literature, yet these methods are often not mentioned, with other, less general, methods being taught, e.g., tin/concentrated hydrochloric acid, zinc/acid, and lithium aluminum hydride. Where multiple methods are taught, the rationale for inclusion of these is often not presented, particularly considering functional group compatibility, ease of purification, safety, or sustainability. Considering the textbooks reviewed, the mechanisms involved in the reduction are generally not discussed. We argue that, despite the perceived complexity of the reaction, coverage of the sequential nature of the reduction is important in aiding students’ understanding of this reaction, e.g., to account for the formation of various intermediates and/or byproducts. We present suggestions to enable educators to discuss the processes involved in this important transformation, drawing parallels with the presentation of other frequently taught reaction pathways.

Here, we present a laboratory activity in which the students work on an analysis of a questioned document that was written with one out of five possible pens. As a forensics study, the activity applied chemistry and analytical chemistry tools to solve the case. The students were able to apply polarity and solubility concepts to select and discard some pens. They also learned the basics of fluorescence and the possibilities of using it to detect falsifications. Then, they were able to set up the detection conditions for the HPLC-UV analysis by studying the absorbance behavior of the blue dyes. Finally, the students identified the pen used to write the suicide note and partially characterized the composition of the ink. This multipurpose activity perfectly suits subjects involving analytical techniques and forensics for students with basic knowledge of chemistry that are studying instrumental techniques for the first time.

pH determination and acid–base titrations are essential experiments performed by high school and university undergraduate students alike throughout their chemistry education. While these experiments often rely on conventional pH meters for quantification and pH test strips or indicators for qualitative assessments, we demonstrated herein that a smartphone-based pH determination technique, performing digital image analysis, particularly the determination of either the dominant wavelength or the RGB intensities, could readily replace all but one conventional pH meter in a classroom setting. Using an in-house developed smartphone-based pH reading application (app), students were able to determine the pH and perform titrations using pH strips and universal indicators, producing results matching those determined with a standard pH meter. The app and its “variants” are available for download (https://tinyurl.com/2dashjyk and https://tinyurl.com/4d73wnxt), and no prior knowledge of coding or programing was required from the students. All that was needed was an Android 11 phone or tablet with an Internet connection. Moreover, the students and instructors’ reactions to the mobile app alike were very positive and showcased the need and interest for such inexpensive technology, which allows for the running of an entire class for pH determination of multiple real-life samples or acid/base titration without using standard pH meters.

Success in general chemistry requires active engagement with course material. COVID-19 accelerated the move to online courses, creating a crucial need for engaging course activities. The Mysterious Compound chemistry game was designed to engage undergraduate students in introductory chemistry concepts while allowing the instructor and students to assess students’ confidence in course concepts. When comparing pre- and postsurveys, there were significant differences (p < 0.001) in students’ confidence levels on all the topics included. Positive and negative feedback was elicited and analyzed through student surveys. This game is an easy-to-implement engagement tool due to its versatile online format and adaptable design.

Tofu, a traditional Chinese food, is now popular worldwide. However, few people notice the chemistry that is involved in its production. To shed light on this, we have designed a simple demonstration for lower-level undergraduates in organic chemistry or biochemistry courses to help them understand the chemistry principles that underlie the curdling step in tofu processing. Raw soymilk is relatively stable without heating, even with the addition of coagulants. However, heat treatment denatures the soy proteins in soymilk, which makes them more amenable to coagulation. This coagulation is further promoted with salt coagulants, such as calcium gluconate, zinc gluconate, and calcium lactate. Acid coagulants such as white vinegar or grape, orange, and lemon juice can also induce coagulation due to their acidic properties. Based on our results and on previous reports, we illustrate the curdling mechanism in this work. This demonstration can also be used as an at-home experiment during lab closure situations, such as a pandemic, and can arouse students’ curiosity about the coagulation of other food proteins and the process of making alternative tofu.

Valence shell electron pair repulsion theory (VSEPR) as explained in most textbooks predicts that substituents bonded to a central atom in AX_nE_z^c species (A = main-group central atom, X = substituent, E = lone pair on central atom, c = charge) will change their X–A–X angles to bend away from the lone pairs. Exceptions have appeared in the literature, commonly arising from steric repulsions between very large substituents and less commonly from electronic factors such as multiple bonding and bond polarization. We have conducted extensive computational studies of hypercoordinate main-group molecules and ions AX_nE_z^c and AO_mX_nE_z^c, where X = halide, and found that VSEPR-based predictions of such bending for those species containing heavier halides are likely incorrect. Indeed, despite the fact that cases where X = F usually conform to the prediction, we find that IOF₄^–/XeOF₄ and IO₂F₂^–/XeO₂F₂ should not. Calculations of the electron localization function indicate that the root cause of the difference is the migration of lone pairs closer to the central atom. We recommend that presentation of VSEPR in general chemistry and inorganic chemistry textbooks be revisited and provide suggested language incorporating this phenomenon.

Hands-on experiences in analytical chemistry laboratories are essential to improve students’ technical skills on handling analytical glassware and instruments, but the coronavirus pandemic in 2020–2021 disrupted such learning activities. Thus, alternative remote activities are required to supplement practical skills. In this work, a new portable experiment to determine the concentration of Fe(III) by digital image colorimetry with curcumin paper is described. This experiment utilized complexation between Fe(III) and curcumin on a paper substrate, which changed from yellow to red-orange. Then, the RGB intensity changes, obtained using smartphones/devices, were plotted against the Fe(III) standard concentration to construct an external standard calibration curve for determining Fe(III) in unknown solutions. Using students’ own smartphone/device enhanced their interest, and the portable small-scale experiment kit enabled a remote hands-on experience at their residence (Lab@Home). The experiment had been implemented both in Lab@Home and in-person formats for three semesters with 591 second-year students majoring in chemistry and other sciences, showing a satisfactory self-evaluated outcome (4.27 from 5) and post-test score (81.5%). The proposed experiment is a showcase to introduce modern analytical chemistry through smartphone/device and digital image colorimetry, while enhancing students’ skills and interests in analytical chemistry laboratory.

By organizing an extracurricular seminar, based on the analysis of the intermolecular dispersion action in normal alkanes, a new topological index (named “Intermolecular Interaction Index (IMI)”) was proposed to express the intermolecular dispersion force. The IMI has an excellent linear relationship with the boiling point (T_b) of normal alkanes containing carbon atoms C₂–C₄₀ (standard error only 0.87 K). For T_b of branched alkane isomers, only the addition of a parameter ΔAOEI (“average odd–even index difference”) is needed to establish the correlation equation. The seminar activity promotes students’ ability for molecular structure–property reasoning and provides students with a preliminary understanding of the molecular graph, topological index, and principle of development of quantitative structure–property relationship (QSPR) models.