Showing papers in "Journal of Chemical Education in 1996"
TL;DR: In this paper, a general overview of the principles of supercritical fluid extraction is presented and the instrumentation necessary to carry out an extraction using a supercirtical fluid is described.
Abstract: While the research and industrial communities are wholehartedly embracing the use of supercritical fluid extraction (SFE) technology, little has been written about it in undergraduate texts or in educational journals such as the Journal of Chemical Education . The supercritical phenomenon of fluids was first discovered in the early 1800's by the Frenchman Baron Charles Cagniard de la Tour, but the significance and practical application of his discovery have only recently been recognized and achieved. This article presents a general overview of the principles of SFE and describes the instrumentation necessary to carry out an extraction using a supercirtical fluid. The reader will also gain insight into the types of research currently being conducted using supercritical fluids as either processing solvents or as reaction constituents and matrices. Because carbon dioxide is the supercritical fluid of choice for many procedures, its use and modification for specific solutes is covered in some detail.
158 citations
TL;DR: In this article, questions based on or incorporating microscopic representations were used to evaluate student understanding of such chemical concepts, such as acids and bases, acid strength, dissociation, diatomic elements, bonding, and aqueous solutions.
Abstract: Students often learn how to solve mathematical problems without understanding the chemistry. They memorize chemical definitions and use chemical terms without true comprehension. Misconceptions regarding acids and bases, acid strength, dissociation, diatomic elements, bonding, and aqueous solutions can interfere with subsequent learning and can persist beyond the undergraduate levelThese chemical concepts readily lend themselves to microscopic representations. Teaching strategies using these visual aids could explain the concept before applying the mathematics. This might increase comprehension and retention by allowing students to picture the chemistry. Questions based on or incorporating microscopic representations could evaluate student understanding of such chemical concepts.
155 citations
TL;DR: The optical basicity concept relies on the Lewis approach to acids and bases and was developed for dealing with chemical problems in non-aqueous, non-protonic media such as silicates, phosphates and borates which are important in glass making and (as slags) for refining steel.
Abstract: The optical basicity concept relies on the Lewis approach to acids and bases and was developed for dealing with chemical problems in non-aqueous, non-protonic media such as silicates, phosphates and borates which are important in glass making and (as slags) for refining steel. Basic oxides such as Na2O or CaO are ionic while SO3, P4O10 or SiO2 are covalent, and it is the magnitude of negative charge borne by the oxygen atoms or ions which governs the degree of acidity or basicity. The oxygen atoms of sulfates, phosphates or network systems such as silicates bear charges which are between those of their parent oxides. In principle, the negative charge can be estimated using the optical (ultraviolet) spectra of certain probe ions and is represented by the optical basicity value, Lambda. Optical basicity values, available for 16 oxides, increase from the acidic SO3 to the very basic Cs2O in a way which conforms with electronegativity and polarizability. The optical basicity concept also extends to fluorides ...
106 citations
TL;DR: The relationship between mathematical SAT scores (SAT-M) and grades earned by students in eight consecutive years of first and second-semester general chemistry courses at Oberlin College are reported as mentioned in this paper.
Abstract: The relationships between mathematical SAT scores (SAT-M) and grades earned by students in eight consecutive years of first- and second-semester general chemistry courses at Oberlin College are reported. The academic years surveyed are 1987-1988 through 1994-1995. SAT-M scores are grouped within seven ranges from 450 and less to 710-800. Within any range of scores, students in both courses earned a wide variety of grades, but those within the higher ranges tended to earn higher grades and fewer failures relative to students in the lower ranges. For all students within each range of SAT-M scores, the fraction earning each grade are calculated. These fractions along with the numbers of students and their SAT-M scores in a subset are used to calculate grades expected for that subset. In the first-semester course, the expected and actual grades for subsets of males, females, first-year students, non-first-year students, Asians, Blacks, and Latinos are not significantly different. Those who eventually majored in chemistry or biochemistry attained grades very significantly higher than expected. Most students tended to achieve grades in the second-semester course that were similar to those earned in the first-semester course.
91 citations
TL;DR: In this paper, a proposed application of concept maps in chemistry teaching in high schools is presented and illustrates a proposed approach for applying concept maps to chemistry teaching, where the students were provided with the "concept lables" necessary for map building in three different ways.
Abstract: This article presents and illustrates a proposed application of concept maps in chemistry teaching in high schools. The students were provided with the "concept lables" necessary for map building in three different ways. The analysis of the students' maps at different stages of the learning process led to the recognition of the three types of cognitive events which seem to correspond to the same number of restructuring stages in the conceptual organization. This can enable the teacher to characterize the changes produced in the learners' conceptions by teaching / learning activities. Three examples of the use of concept maps in chemistry teaching are reported and discussed with reference to: atomic structure, oxidation-reduction and thermodynamics.
88 citations
TL;DR: In this article, the behavior of HSAB in aqueous solution is addressed and a quantitative scale of hardness-softness for acids and bases is presented also, where the hardness of base acids and acids is defined.
Abstract: The idea of hard and Soft Acids and Bases (HSAB), developed by R. G. Pearson some 30 years ago, has been used as a unifying principle in several texts. In spite of this, HSAB has remained qualitative and largely intuitive. In this article, the behaviour of HSAB in aqueous solution is addressed. A quantitative scale of hardness-softness for acids and bases is presented also.
84 citations
TL;DR: In this paper, the microscale syntheses of Tetraphenylporphyrin, H2(TPP), and the corresponding metalloporphyrins ZnII(TPP) and NiII( TPP) are reported.
Abstract: The microscale syntheses of Tetraphenylporphyrin, H2(TPP), and the corresponding metalloporphyrins ZnII(TPP) and NiII(TPP) are reported. H2(TPP) is synthesized by the condensation of benzaldehyde and pyrrole, and the subsequent metallation of H2(TPP) is achieved with anhydrous ZnIICl2 or NiIICl2 in DMF. The compounds are analyzed by their electronic absorption spectra in the visible region, and by their fluorescence properties. The visible spectra are obtained on a Spectronic 20 spectrophotometer. Analysis of the electronic absorption spectra is presented on the basis of ZnII(TPP) representing the class of regular metallporphyins, and NiII(TPP) representing the class of hypsoporphyrins. The hypsochromic (blue) shifts of the NiII(TPP) complex is discussed in terms of significant metal to ligand pi-backbonding. A group theoretical interpretation of the simplified electronic absorption spectra of the metalloporphyrins of D4h symmetry, relative to the free-base porphyrin H2(TPP) of D2h symmetry is offered.
78 citations
TL;DR: In this paper, the nature of the chromophores found in cellulose, hemicellulose and lignin-containing papers and the mechanism for photoyellowing are discussed.
Abstract: The discoloration of paper on aging is of interest to the archival community and also to the pulp and paper industry where new and improved mechanical pulps are being developed. The yellowing of paper on aging can be attributed to the presence of chromophores found in some of the products formed from the degradation of one or more components of paper. This study identifies the nature of the chromophores found in cellulose, hemicellulose and lignin. The photooxidation of lignin-containing papers and the mechanism for photoyellowing are discussed. This is followed by a description of the basic principles of conservation bleaching which involves chemically treating papers in order to remove unwanted discoloration or stains. The washing of paper and the use of oxidizing and reducing bleaches are presented. The discussion on oxidizing bleaches includes hydrogen peroxide, alkaline hypochlorite, chlorine dioxide and sunlight. The chemistry of reducing bleaches focuses on dithionites and borohydrides.
73 citations
TL;DR: In this article, the origins of electronegativity as a qualitative concept in the period between 1809 and 1813 are discussed, and the intent of the present paper is to recapture some of the early pre-Pauling history of the concept.
Abstract: The intent of this paper is to recapture some of the early pre-Pauling history of electronegativity. In doing so, I hope to remind the modern theorist that those who ignore history always run the risk of repeating it--a cliche, no doubt, but unhappily one that embodies a sizable, albiet depressing, amount of the truth. The subject is approached in three stages. Here in Part I the origins of electronegativity as a qualitative concept in the period between 1809 and 1813 are discussed.
68 citations
TL;DR: In this paper, a simple laboratory preparation of partially neutralized, cross-linked poly(acrylic acid) is given along with test methods suitable for measuring the absorption capacity of the product.
Abstract: Superabsorbent polymers are cross-linked polyelectrolytes. Because of their ionic nature and interconnected structure, they absorb large quantities of water and other aqueous solutions without dissolving. This makes them ideally suited as absorbents of body fluids in many personal care products sold today, including baby diapers, adult incontinence products, and feminine napkins. Several emerging applications are also described. A simple laboratory preparation of partially neutralized, cross-linked poly(acrylic acid) is given along with test methods suitable for measuring the absorption capacity of the product. Experiments are described that demonstrate the ability of a swelling gel to perform work, and the ability of a gel to exclude macromolecular solutes from diffusing into its porous, cross-linked structure.
TL;DR: The acidity of aqueous solutions of positive ions is never zero although many texts say incorrectly that most metals of Groups I and II and some others are not acidic as mentioned in this paper.However, the few cases in which acidity may usually be regarded as negligible but not zero, include the Group I metals other than lithium and quaternary ammonium ions and similar ions that cannot form a coordinate bond to a water molecule.
Abstract: The acidity of aqueous solutions of positive ions is never zero although many texts say incorrectly that most metals of Groups I and II and some others are not acidic. The few cases in which acidity may usually be regarded as negligible, but not zero, include the Group I metals other than lithium and quaternary ammonium ions and similar ions that cannot form a coordinate bond to a water molecule. The acid constants of metal ions are given in Table I one of the article.
TL;DR: In this article, the authors report results from one such study, Project REMODEL, which set out to narrow the gap between conceptual and algorithmic understanding in freshman chemistry and implemented and evaluated innovations in lecture, laboratory, and assessment for students in the introductory sequence for majors, in order to provide the chemical education community with data on effective innovations and data on the barriers to successful reform.
Abstract: Research has shown that students consistently achieve algorithmic understanding of chemical concepts more readily than the conceptual understanding we wish that they would also acquire. Concomitant with this research, chemical educators have increasingly called for reform in the way in which undergraduate chemistry is taught. The National Science Foundation has supported major initiatives to experiment with ways to change both the curriculum and the manner in which instruction is delivered. This paper reports results from one such study, Project REMODEL.In REMODEL, we set out to narrow the gap between conceptual and algorithmic understanding in freshman chemistry. We implemented and evaluated innovations in lecture, laboratory, and assessment for students in the introductory sequence for majors, in order to provide the chemical education community with data on effective innovations and data on the barriers to successful reform. This paper reports on lecture and assessment innovations in the second semeste...
TL;DR: In this article, the authors provide an engaging high-tech demonstration suitable for illustrating thermodynamic principles in the classroom using thermoelectric devices and demonstrate how to use them in a classroom environment.
Abstract: Thermoelectric devices provide an engaging high-tech demonstration suitable for illustrating thermodynamic principles in the classroom.
TL;DR: This paper analyzed what grade 12 and university students of chemistry should "know" (declarative knowledge) and "know how to do" (procedural knowledge, in terms of reasoning) concerning the geometry and polarity of molecules, and diagnose the conceptual and procedural difficulties that the students could have to achieve meaningful learning of these chemical concepts.
Abstract: Research evidence has shown that students often have views of scientific concepts that differ from those generally accepted by the scientific community. In chemistry, research on student understanding and misconceptions has been conducted in several conceptual areas. Recent studies have been carried out on misconceptions of covalent bonding and structure of molecules. According to the constructivist models of learning, the persistence of these learning difficulties could be explained because traditional teaching doesn't pose as an aim the conceptual change of students. In our opinion, it requires taking into account not only the students' previous ideas, but also the ways of reasoning they use to form their constructions.
The aim of this paper is to analyze what grade 12 and university students of chemistry should "know" (declarative knowledge) and should "know how to do" (procedural knowledge, in terms of reasoning) concerning the geometry and polarity of molecules. At the same time, we try to diagnose the conceptual and procedural difficulties that the students could have to achieve meaningful learning of these chemical concepts.
TL;DR: In this paper, a simple general relationship is presented for the evaluation of the error in a function of several variables and its application to a range of chemical problems is illustrated, and the relationship between the error and the application of the errors to a wide range of problems is discussed.
Abstract: A simple general relationship is presented for the evaluation of the error in a function of several variables and its application to a range of chemical problems is illustrated.
TL;DR: This paper used active, inductive, and cooperative learning to address a broad spectrum of learning styles in chemistry courses and found that the approach enhances understanding and promotes the development of a variety of interpersonal and thinking skills.
Abstract: Five chemical engineering courses were taught to a cohort of students in consecutive semesters using an instructional model based on active, inductive, and cooperative learning and other methods designed to address a broad spectrum of learning styles. The results suggest that the approach enhances understanding and promotes the development of a variety of interpersonal and thinking skills, and that while it may initially provoke resistance from some students, the resistance can be overcome if the methods are implemented with care. With suitable modifications for content differences, the model may be equally effective for chemistry instruction.
TL;DR: In this paper, an attempt was made to bridge the gap between the concepts and algorithms by altering the instructional method in general chemistry courses, which emphasized conceptual problem solving in the initial phase of a concept.
Abstract: There is a gap between the algorithmic problem solving abilities of chemistry students and their conceptual understanding of the chemistry. This gap persists because many chemistry instructors allow students to hide their lack of conceptual understanding behind correct numerical answers. If the goal of chemistry instruction is to have students think about and solve conceptual problems as well as algorithmic problems then the approach to chemistry instruction must change. This is a report of a study where an attempt was made to bridge the gap between the concepts and algorithms by altering the instructional method in general chemistry. This approach emphasized conceptual problem solving in the initial phase of a concept. The approach was implemented simultaneously in general chemistry courses designed for science majors and non-science majors. The study provided some interesting data with regard to the response of science majors and non-science majors to this conceptually oriented instructional approach. These responses provide some interesting insight into the ways in which the two groups of students have been socialized with regard to science.
TL;DR: The Student-Directed Learning (SDL) method as mentioned in this paper encourages increased selfconfidence, independence, and awareness of the student's role in the teaching/learning process by incorporating four criteria for acceptance of responsibility: student ownership, student active learning, student accountability, and student control.
Abstract: One of the frustrations of teaching is the failure of talented students due to lack of effort on their part. We have to admit that Organic chemistry presents many challenges to students. At the same time we are aware that students often defeat themselves by a combination of procrastination and cramming. The Student-Directed Learning (SDL) method discourages this student strategy. Instead SDL fosters increased self-confidence, independence, and an awareness of the student's role in the teaching/learning process. This method incorporates four criteria for acceptance of responsibility: student ownership, student-active learning, student accountability, and student control. With SDL the course content is reorganized to make it more accessible to students. Learning modules are centered around "The Big Ideas". Each big idea is connected to its usefulness in pharmaceutical science, or is identified as a foundation idea for understanding subsequent course material. The class session is changed from traditional le...
TL;DR: One-Minute Paper as discussed by the authors has been proposed as a tool to provide active learning in the classroom and has been used in a large general chemistry class at a major university over the past five years.
Abstract: In a large general chemistry class it is important to generate good communication between students and teacher. Ideally there should be instantaneous feedback between the student and professor. One tool to help improve communication and class attention is the "One-Minute Paper". A One Minute Paper given at the end of each lecture has been proposed as a tool to provide active learning in the classroom. This paper describes and evaluates the technique based on its use in a typical general chemistry class at a major university over the past five years.
TL;DR: In this article, it is argued that course reform should be linked to authentic student achievement, so that students can actively experience the feelings of practicing professionals, and that a need exists to move from the passive learning styles that have characterized chemistry courses to an active style in which students participate and assume responsibility for their learning.
Abstract: It is recognized that a need exists to move from the passive learning styles that have characterized chemistry courses to an active style in which students participate and assume responsibility for their learning. In addition, it is argued that course reform should be linked to authentic student achievement, so that students can actively experience the feelings of practicing professionals.
TL;DR: In this paper, the inner and outer-sphere mechanisms for complex charge transfer reactions in homogeneous phase have been applied to heterogeneous charge transfer reaction reactions, and the influence of these mechanisms, on the electrochemical behavior of a redox couple, is presented through comparison of the responses obtained by cyclic voltammetry and rotating disk voltammetric in different metallic substrates, for the [Fe(CN)6]3/[Fe[CN]4]4- in sodium nitrate (outer sphere mechanism) and Fe(III)/Fe(II)
Abstract: The concepts of inner- and outer-sphere mechanisms for complex charge transfer reactions in homogeneous phase have been applied to heterogeneous charge transfer reactions. The influence of these mechanisms, on the electrochemical behavior of a redox couple, is presented through comparison of the electrochemical responses obtained by cyclic voltammetry and rotating disk voltammetry in different metallic substrates, for the [Fe(CN)6]3-/[Fe(CN)6]4- in sodium nitrate (outer sphere mechanism) and Fe(III)/Fe(II) in sulfuric acid medium (inner sphere mechanism). The obtention of quantitative evidence of these differences is also showed by the calculation of the kinetic parameters for these couples.
TL;DR: The design of a biochemistry course that uses problem-based learning and principle concepts and engagers encountered in this course are identified and pedagogical advantages derived from science course is discussed.
Abstract: This article describes the design of a biochemistry course that uses problem-based learning. Examples of some of the problems incorporated into the course are described in detail. Principle concepts and engagers encountered in this course are identified. Pedagogical advantages derived from science course is discussed.
TL;DR: This article showed that only low molecular weight, volatile compounds were amenable to analysis by conventional mass spectrometric methods and most larger species simply could not be promoted into the gas phase.
Abstract: Until recently only low molecular weight, volatile compounds were amenable to analysis by conventional mass spectrometric methods. Most larger species simply could not be promoted into the gas phas...
TL;DR: This paper surveyed 35 modern and classic texts to learn what each noted of Wohler's work, and found that these books do not agree about the exact nature of the experiment and its significance.
Abstract: Most general chemistry and organic chemistry textbooks describe Friedrich Wohler's synthesis of urea as the moment when modern organic chemistry was born. We surveyed 35 modern and classic texts to learn what each noted of Wohler's work. These books do not agree about the exact nature of Wohler's experiment and its significance.
TL;DR: In this article, the authors report on the difficulties experienced by students in relation to electrode processes and terminology and aspects of cell components, cell emf, and current, as well as the responses of a larger group of students.
Abstract: Four areas that present difficulty among high school pupils and tertiary level students in relation to the processes that take place in operating electrochemical cells were identified (1). These are (i) conduction in the electrolyte, (ii) electrical neutrality, (iii) electrode processes and terminology, and (iv) aspects relating to cell emf, current, and cell components. A 20-item questionnaire was designed to determine how widespread misconceptions in these areas were. The prevalence and possible causes of misconceptions in two of the four areas - namely, conduction in the electrolyte and electrical neutrality - were reported (2). In this paper, we report on the difficulties experienced by students in relation to electrode processes and terminology and aspects of cell components, cell emf, and current. In relation to electrode processes and terminology, excerpts from interviews with precollege and college students as well as the responses of a larger group of students are discussed. The discussion relating to cell components, cell emf, and current presents a response to standard textbook questions by precollege and college students and interviews conducted with postgraduate higher diploma in education (HDE-PG) students. The interviews were conducted with postgraduate students after the precollege and college students were unable to verbalize their views, especially on cell emf and current. The possible causes of the misunderstandings and the questions used to elicit the misunderstandings in these two areas are presented.
TL;DR: One of the more interesting new items in health-food stores is conjugated linoleic acid (CLA) as mentioned in this paper, which is a conjugation of linolenic acid.
Abstract: One of the more interesting new items in health-food stores is CLA, conjugated linoleic acid. Its diverse effects suggest that it is involved in one or more of the most fundamental aspects of cell structure and chemistry.
TL;DR: In this paper, the chemical reactions that are responsible for the aging of paper are discussed with the conclusion that acid-catalyzed hydrolysis is the predominant mechanism for cellulose degradation and strength loss.
Abstract: This study provides an introduction to the problem of the aging of paper and the conservation techniques that are currently being employed in paper preservation. The chemical reactions that are responsible for the aging of paper are discussed with the conclusion that acid-catalyzed hydrolysis is the predominant mechanism for cellulose degradation and strength loss. A description and the chemistry of a number of mass deacidification methods are presented. The more viable deacidification methods include the DEZ, Wei T'o, FMC, Bookkeeper, Viennese, Book Preservation Associates, Sable and the Batelle processes. A summary of the literature on the evaluations of these processes is presented, and the benefits and limitations of the mass deacidification methods are discussed. Other conservation techniques such as paper strengthening, conservation bleaching, and pest control are briefly introduced, followed by an introduction to alkaline papermaking.
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TL;DR: The ECW model is a powerful tool for developing an understanding of donor-acceptor interactions as discussed by the authors and has been used to predict enthalpies of adduct formation but overlook the application of the E and C parameters as a scale to analyze reactivity and spectroscopy.
Abstract: The ECW model is a powerful tool for developing an understanding of donor-acceptor interactions. Most modern inorganic chemistry textbooks discuss the model's ability to correlate and predict enthalpies of adduct formation but overlook the application of the E and C parameters as a scale to analyze reactivity and spectroscopy. Furthermore, a survey of these textbooks indicate the authors are using parameters of different vintages. This article provides the teacher with the latest parameters as well as an update of the traditional uses of the ECW model and a discussion of some of the more important, often overlooked, applications of the model.
TL;DR: In this article, the authors describe a change in the position of a UV-Vis absorption band with the change in solvent polarity, which is a sign of a change of solvatochromism.
Abstract: Solvatochromism is used to describe a pronounced change in the position of a UV-Vis absorption band with a change in solvent polarity.