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Gases : IDGasFromVelocity (8 Variations)
The following are graphs of molecular velocities versus the relative number of molecules for argon, chlorine, methane and xenon at 300K. Which graph is for argon?
Molecular Models of Peroxides and AlbendazolesWilliam F. Coleman This month's Featured Molecules are albendazole and benzoyl peroxide. Coleman, William F. J. Chem. Educ.2008, 85, 1710.
Consumer Chemistry |
Molecular Properties / Structure |
Molecular Modeling
Molecular Models of Natural ProductsWilliam F. Coleman This months Featured Molecules focus on natural products and include blattellquinone, a sex pheromone secreted by female German cockroaches to attract males, and (R)-limonene, a secondary metabolite found in citrus fruit peels. Coleman, William F. J. Chem. Educ.2008, 85, 1584.
Molecular Modeling |
Molecular Properties / Structure |
Natural Products
Molecular Models of Polymers Used in Sports EquipmentWilliam F. Coleman The Featured Molecules this month are a number of monomers and their associated polymers used in making equipment for a variety of high-impact sports. The molecules provide students with an introduction to an important area of applied chemistry and also enable them to examine complex structures using the models they have seen applied to small molecules. Coleman, William F. J. Chem. Educ.2008, 85, 1456.
Molecular Models of IndicatorsWilliam F. Coleman The article by Nicholas C. Thomas and Stephen Faulk on "Colorful Chemical Fountains" (1) reminds us that color—the colors of acid–base indicators or of metal complexes—is responsible for many of us developing an interest in chemistry. The featured molecules this month are the acid and base forms of three common indicators–phenolphthalein, methyl orange, and methyl red. These three substances display interesting structural features as the pH-induced transformation from one form to another takes place in three different ways. In the case of phenolphthalein, the lactam ring is cleaved on deprotonation to produce a carboxyl group with the concomitant removal of a proton from a phenolic group. In methyl orange, one of the nitrogen atoms is protonated in the acid form, and that proton is lost in the base form. In methyl red, a carboxylic acid function is deprotonated. There are many other interesting aspects of acid–base indicators. Since most plants and fruits contain pigments that show a color change in some pH range, it is difficult to state with any degree of certainty when these changes were first put to use in a systematic fashion. The Spanish alchemist Arnaldus de Villa Nova (Arnold of Villanova) is purported to have used litmus in the early 14th century. In general systematic use of indicators is traced to the latter half of the nineteenth century with the development of the three synthetic indicators described above. Many students will be familiar with the use of phenolphthalein to identify blood—often shown on the various forensic chemistry TV dramas by dropping some solution on a cotton swab that has been used to pick up some of the sample in question. If the swab turns red we frequently hear "It's blood". The reality of using phenolphthalein in this way is more complicated. The test is presumptive for the presence of blood, but not conclusive. It is not an acid–base reaction but rather, in the presence of hydrogen peroxide, relies on hemoglobin to catalyze the oxidation of phenolphthalein. An interesting assignment for students in a high-school or non-majors course would be to have them explore the details of this Kastle–Meyers test to see just what is involved in the correct application of the test, and what factors complicate the process. For example, would tomato juice infused with asparagus juice give a positive Kastle–Meyers test? Historically phenolphthalein was used in a variety of laxatives. Recently that usage has been discontinued due to concern about the carcinogenic nature of the substance. A review of the history of the controversy surrounding the use of phenolphthalein in laxatives would make a good research paper at the high-school level. Lastly, students with some practice building structures and performing calculations might wish to explore the structures of two other forms of phenolphthalein—one found in very acidic solutions, having an orange color, and one found in very basic solutions that is colorless.
Molecular Properties / Structure
Inorganic Molecules; A Visual DatabaseCharles E. Ophardt, Evan M. Davis, Dustin Underwood Inorganic Molecules: A Visual Data Base contains text and graphics describing 66 molecules and ions commonly used as examples in general chemistry courses. For each molecule, fifteen molecular properties are presented visually by eight or nine different molecular models created by the CAChe Scientific Molecular Modeling program.
Atomic Properties / Structure |
MO Theory |
Molecular Properties / Structure
The Shapes of MoleculesEd Vitz, John W. Moore A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
