Hands-On Experiment to Verify Consistency from Bulk Density to Atomic and Ionic Radii with Lumps of Metals and Ionic Compounds

A hands-on experiment to obtain atomic and ionic radii with lumps of metal and ionic compounds is reported here. The experiment is performed with industrial-grade typical metals (iron, copper, aluminum, and lead) and single-crystal lumps of ionic compounds (sodium chloride, potassium chloride, and potassium bromide). Students measure the dimension of the given lumps with Vernier calipers and weigh them with a precision balance. After measuring the dimension and mass of the given lumps, students can calculate the atomic and ionic radius of each corresponding atom and ion with the obtained density values and information about the lattice structures. The obtained values of the metal atomic radii and the ionic radii of the ionic compounds are very close to the values in the literature. After this activity, the students came to appreciate that atomic radii, as typical submicroscopic and symbolic representations, are actually existing features and not an abstract concept. The experiment reported here is suitable for a first-year undergraduate general chemistry class as well as an introductory class at the high school level. © 2019 American Chemical Society and Division of Chemical Education, Inc.1

Electrolysis: What textbooks don’t tell us

We present a critical discussion of how chemistry textbooks treat the electrolysis of water and aqueous salt solutions, based on a survey of general chemistry textbooks in English and Korean at secondary and tertiary levels, also informed by the historical background of 19th-century debates. English-language textbooks present various and contradictory accounts of the electrolysis of water; a key point of disagreement is whether hydrogen and oxygen gases originate from pre-existing H+and OH−ions, or from the direct reduction and oxidation of H2O molecules. School textbooks in South Korea all present the same account, with no indication of alternative views. A vast majority of all texts ignore the possibility that H2and O2may result from secondary reactions, which was a standard view in the late 19th century following the works of Daniell and Miller. Concerning the electrolysis of aqueous salt solutions, all texts give oversimplified views of competing reactions based on standard reduction/oxidation potentials. It is understandable that textbooks try to present sufficiently simple pictures that students at each level can handle; however, this should not be done in a way that shuts down questions. We recommend that students should be made aware that textbook accounts are only models, and encouraged to extend their learning beyond the models. The plausibility of our recommendations is shown in a pilot study we conducted with secondary school students in South Korea.</p