Two indices addressing buffer solution are differentiated, which are used to gauge punctual and durative buffer function, respectively. Buffer strength β and buffer capacity α are accordingly suggested for the names of the indices (their corresponding mathematic expressions are differential formula and integral formula, respectively). The feasibility of introducing differential formula into calculation of durative capacity in the textbooks is intensively discussed, and the applicable conditions of this practice are pointed out, which forms the basis of suggestions for improvement on some contents of the textbooks.
Conservation law is widespread in nature. Analytical chemistry is often related to many conservation laws, such as material conservation, charge conservation, proton conservation, electron conservation, etc. In analytical chemistry, conservation laws can be used to derive many formulas and to solve some complex calculation problems. In long-term teaching practice, the writers find that conservation laws can help students to understand many formulas, simplify the complicated process, consider the problem on an overall perspective, and not to consider trivial details.
For complex acid-base solution system, it is difficult to deal with the proton equilibrium condition and deduce its proton balance equation (PBE). In this paper, taking FeCl3 aqueous solution as a model, we discuss the treatment for proton equilibrium condition, and deduce systematically the proton balance equations based on various equilibrium relations in acid-base solution. These derivation results of PBE have been verified by different methods.
Two-dimensional NMR (2D NMR) is an effective tool for analyzing complex organic molecules and accurate assignments of their NMR signals. Herein, we showed three applications of 2D NMR on the structural analysis of complex molecules. Compared with 1D NMR, 2D NMR is advantageous due to the fact that it resolves the overlapped NMR signals much better by presenting those important parameters (chemical shifts and coupling constants, etc.) in two dimensions. In addition, 2D NMR provides the information of mutual-interactions of various nuclei. Therefore, 2D NMR can definitely help students to analyze the complex organic molecules.
The Limit of Detection and Sensitivity of analytical methods are two basic parameters for evaluating analytical methods. The International Union of Pure and Applied Chemistry (IUPAC) clearly recommends their definitions. However, both of them are still somewhat confused in some textbooks and research papers of analytical chemistry. Here, the definitions of both Limit of Detection and Sensitivity are clearly presented and the influence factors on Limit of Detection and Sensitivity of modern analytical methods are discussed. Some strategies to improve the Limit of Detection and the Sensitivity are proposed.
According to the general principles of classification and definition of concepts the concepts in the course of chemical analysis addressing metrical data are sorted out, including the basic tasks of chemometrics, accuracy, precision and error. Discussions are carried out on the arrangement of contents, concept terminology and definition of some concepts in the currently popular textbooks, and relevant suggestions are put forward, in the hope of providing reference for refining the textbooks of《Chemical Analysis》and standardizing academic terminology.
In HF solution and HF-F- solution, there are not only the dissociations of hydrofluoric acid but also the reactions between hydrogen fluoride and fluoride ion, so the equilibrium concentration of each component is the final product of two equilibria. Theoretically, the correct result can be obtained only if the two equilibria are considered simultaneously. However, much attention has been paid to the dissociation equilibrium of HF than to the HF-F- association in teaching, as a result students are used to take the wrong calculation method when confronting such problems. In order to develop students' comprehensive abilities to deal with the calculations of complex systems, the simple and accurate formulas for calculating the ion concentrations in HF solution and HF-F- solution are derived based on multi-equilibrium. By comparison, it is found that both equilibria must be considered in all cases, except that the concentration of HF solution is less than 1.91×10-2 mol·L-1 which can be approximately calculated as monobasic weak acid.
Organic substance has been considered as organic compound, but the author does not think it's accurate. C60 should belong to organic substance according to its structure and properties. Based on this fact, a common understanding will be formed: organic substances include both some carbonaceous elementary substances (e.g. C60) and the vast majority of carbonaceous compounds.
This paper introduces the description in application of the theory of valence shell electron pair repulsion in textbooks at home and abroad. The main methods for determining the number of valence-layer electrons of the central atom are compared and analyzed, including the methods based on Lewis electronic determination method, the group number of the central atom and the number of electrons provided by the coordination atom, the valence electron number of the center atom in the ground state and the unpaired electron number of the coordination atom, and the total number of valence electrons of related atoms in the ground state and octet rule of coordination atoms. The theoretical basis and the physical meaning of the different methods are expounded. The main aim is to develop a consensus on this fundamental chemical theory to make it easy for the students to understand and master.
Five typical specious questions in polymer chemistry were discussed, including "the criterion of the spontaneity of a polymerization is △G < 0", "the activities of the two kind of active centers in an ideal copolymerization are the same", "ferrocenylmethyl acrylate (FMA) has a higher propagation rate constant of homopolymerization than 2-ferrocenylethyl acrylate (FEA)", "Methyl 3-(4-methylphenyl)-2-propenoate, or Methyl 4-methylcinnamate, can be homopolymerized into high polymer" and "α-cyanoacrylate cannot be free radically homopolymerized". Through raising and answering these questions, the students were encouraged to think, to doubt, to question, to explore, to acquire, and to understand under the teacher's inspiration and guidance. This helps to train the critical thinking skills, the problem conversion ability and the literature consulting awareness, to build the awareness and abilities of problem finding and problem raising, and to develop the ability to analyze and solve problems, in addition to acquire the right knowledge.
A variety of domestic and international organic chemistry textbooks hold the standpoint that the two resonance structures of benzene are Kekulé structures. By introducing the research history of benzene structures and the structural characteristics of Kekulé's benzene, we propose that the above standpoint should be reconsidered. We also suggest that the two resonance structures should be named as "Pauling's structure" or "Pauling benzene".
In a variety of the inorganic chemistry teaching materials and related references that the composition to give the strongest buffer capacity at pH=pKa? is not described concisely. We proposed amendment description for buffer capacity in the book written by teaching and research office of Inorganic Chemistry at Dalian University of Technology. The description is based on the distribution curve slope when buffer solution pH as close as possible to pKa?.
After years of teaching inorganic chemistry, it is found that many students lack knowledge of the four quantum numbers in the content of material structure, which seriously affects their learning of the following content. In order to help students to get out of the dilemma, we use analogy teaching method and use the "virtual classroom and teaching building" model to visualize the content of the abstract four quantum numbers. The results show that the students' mastery degree is better than that of previous years, which indicates that the current analogy teaching method has achieved satisfactory teaching effect.
The domestic organic chemistry textbooks use different numbers of contributing structures when introducing the resonance structures of benzene. This paper suggests that some of the related textbooks remove Dewar benzene and other ionic structures from the resonance structures of benzene, and adopt the correct resonance representation which constitutes only two Kekulé structures.
Aromatic electrophilic substitution is a very important method to synthesize different substituted arenes. Its regioselective rule is the theoretical evidence to realize the controlled synthesis of the desired target molecules. Theoretical rationale and experimental evidences on the regioselective rule in the aromatic electrophilic substitution of disubstituted benzenes are discussed here from the viewpoints of stabilities of intermediates, activation energies, and relative reaction rates. It would provide reasonable explanation and experimental evidence for the regioselective rule and is convenient for students to understand correctly.
Rapid development of mass spectrum technology (MS) brings about its wide applications in many fields such as chemistry, material science and life sciences, and its application in biochemistry and chemical biology have been greatly expanding the knowledge of novel protein post-translation modification (PTM). This manuscript starts from the basic principles of mass spectrum and later elaborates the application of MS in discovering lysine post-translation modifications over histones as model proteins, showing a path incorporating fundamental organic chemistry and biochemistry knowledge into cutting-edge researches. By analyzing roles of mass spectrum throughout post-translation modification studies under different research logistics, this manuscript was aimed to help establishing a way of thinking that associates fundamental chemistry and biology education with practical applications for students.
In the acid-base titration curve of titration from NaOH to HAc, shown in the sixth edition of Analytical Chemistry edited by Wuhan University, we found that there was an obvious protruding part of the curve at the initial stage of titration, which was significantly different from the curve of titration from NaOH to HCl at the same concentration. In this paper, the mathematical expression of fitting the curve is derived by using various equilibrium relations in acid-base reaction. The correlation law of acid-base titration is proved by combining with the image of mathematical function. The mathematical model can explain not only the differences between two curves, but also the reasons and influencing factors of the initial titration curve difference of weak acids by strong alkali titration.
Based on the dissociation equilibrium constants of six arsenic species, including arsenic acid, arsenite, monomethyl arsenate, dimethylarsenic acid, arsenicone and betaine, and corresponding distribution fraction at different pH, the retention differences in chromatographic/non chromatographic separation process, and the possible reasons for simultaneous enrichment of these species are discussed. It was used as an example to improve the teaching of the basic concept of "distribution score" in the course of analytical chemistry, and to achieve the teaching goal of deepening cognition, firmly mastering and stimulating interest.
Classroom introduction is the starting link of classroom teaching and plays a key role in the teaching effect of the whole class. Classroom introduction skill is an essential ability for pre-service teachers. Based on classroom observation and analysis of study cases, the author summarizes some typical problems of classroom introduction of pre-service chemistry teachers, such as simple stacking of situational materials, excessive use of negative materials, and tedious introduction design. In addition, attribution analysis is carried out from three aspects, namely, ignoring the function of introduction, insufficient understanding of subject value, and inadequate grasp of skill elements and designing principles. At the same time, combined with the analysis of demonstration cases, the countermeasures are put forward to guide the pre-service chemistry teachers to improve their classroom introduction skills.
The study aims to help students learn efficiently, summarize systematically, and apply knowledge comprehensively regarding the critical aspects of free radical polymerization. A comprehensive problem was proposed to develop their knowledge-comprehensive-application ability, questioning ability, problem-solving skills, critical thinking, and literature consulting awareness. The comprehensive problem, covering all the important aspects of free radical polymerization, was designed accordingly and assigned as team homework. Herein, a new form of problems in polymer chemistry is being developed, the function of problems in polymer chemistry is expanded, students' minds are being opened, and satisfactory results are being achieved.
Strychnine and Brucine are the two main alkaloids in the traditional Chinese medicine Strychnos nux-vomica L. However, the indiscriminate use of Chinese translations makes it difficult for the public to distinguish between Strychnine and Brucine. This has seriously affected the popularization of science and academic communications. We suggest uniform and strict annotations with these alkaloids' English names when the Chinese translations are used.
The general method and key points of obtaining t-plot with instrument software are introduced. The numerical processing method when there is no suitable film thickness equation and reference adsorption line is selected. The method and skill of converting isotherm adsorption line to t-plot with Origin software interpolation method is discussed.
Nuclear magnetic resonance (NMR) is a frequently used spectral method for structural analysis of organic compounds. It is also an important content in the teaching of spectroscopy course. The principle of nuclear magnetic resonance involves some basic concepts including magnetic nucleus, nuclear spin, angular momentum, magnetogyric ratio, electric quadrupole moment, and the change of the internal nuclear energy level distribution in external magnetic field, etc. These concepts are important for the beginners to understand the principle of nuclear magnetic resonance. In this article, the attempt to rationally simplify the complex principle of quantum physics and elucidate the principle from the view of chemistry discipline, and to reasonably integrate ideological and political elements in teaching is discussed. This practice would not only help the students to understand the basic principle in depth, but also cultivate their scientific and systematical thinking and ability to solve complex problems.
This paper provides a primary analysis and discuss on the mathematization of quantitative analysis. By analyzing the present situation of chemical quantitative analysis, instrumental analysis and chemometrics in the establishment and application of mathematical theories, it pointed out that the mathematization of quantitative analysis has not been realized. The mathematization of quantitative analysis should be realized by establishing mathematical equation that contains chemical parameters, is self-contained and can be evolved into mathematical theorem.
The application conditions of pre-equilibrium and steady-state approximations usually used for treatment of complex chemical kinetics are discussed. Based on the characters of opposing reaction, the simplified application conditions for pre-equilibrium approximation is proposed. The shortcoming of the former conditions is pointed out. By defining a dimensionless parameter relating to the discrepancy from steady state and using graphic method, the application conditions of steady-state approximation for the consecutive reaction is clarified. When the rate for consumption of the intermediate is 100 times larger than its generation rate, the error by using steady-state approximation is less than 1%, which is a good approximation.
There are some problems in the condensation polymerization teaching, such as the ratio of function groups, the Polyester linear equilibrium polycondensation kinetic equation, etc. The students were often puzzled with these problems. Based on many years of polymer chemistry teaching experience, these problems were discussed in this paper to provide some reference for peers teaching and students learning.
Understanding redox reactions in reaction of nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+) requires a clear grasp of the textbook content. The reactions in nicotinamide coenzymes with reduced and oxidized forms have been compared in various biochemistry textbooks. Incorrect interpretations usually emphasize the valence changes that at nitrogen in the pyridine ring of a nicotinamide from +5 to +3. Actually, the valence of nitrogen in pyridine ring is -3. We have gathered shreds of evidences and provide here possible suggestions and caution for readers and instructors.
There is no unified equation for calculating titration error in the textbook of analytical chemistry. The Ringbom's equation is the most frequently used, but the equation has problems. This work made a theoretic analysis of the Ringbom's equation based on the definition of titration error. The results show that the calculated end point error using Ringbom's formula is different from that based on the definition. We believe this work can provide fundamental basis for the establishment of reasonable titration error calculation.
This in-class teaching design will facilitate students' understanding of how the basic principles and methods of physical chemistry thermodynamics are used to analyze and correct the literature data calculation process in the field of adsorption. Similarly, it will enhance the accuracy and systematicness of students' knowledge of thermodynamics, as well as promote students' interest and self-confidence in learning by employing such a creative and dynamic classroom teaching model of physical chemistry.
A method for obtaining the delocalized π bonds πnm in a molecule has been discussed in this paper, and the delocalized π bonds πnm in linear, bent, planar trigonal, single cyclic conjugated, and polycyclic conjugated molecules have been studied. The reasons of π34 in NO2 and 2π32 in C3 molecules have been proposed. The delocalized π bonds 2π1818 in cyclo carbon are analyzed.