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Chemistry Textbook Approaches to Chemical Equilibrium and Student Alternative Conceptions

Pedrosa, M. Arminda; Dias, M. Helena
Fonte: University of Ioannina. Department of Chemistry Publicador: University of Ioannina. Department of Chemistry
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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In the field of chemistry there has been considerable interest in discovering the reasons why many students have great difficulty in successfully developing a scientifically accepted understanding of chemical equilibrium. Research projects influenced and inspired by constructivism have been invaluable for identifying alternative conceptions that may turn into obstacles to meaningful learning of fundamental ideas regarding chemical equilibrium. Research findings provide evidence that misunderstandings of and related to chemical equilibrium are widespread at various levels of education, including prospective chemistry teachers. Language used in textbooks may give rise, or reinforce student alternative conceptions and research findings point to a direct relationship between language used in textbooks and some of the alternative conceptions students develop at various levels of school chemistry. Some of the students’ alternative conceptions already identified, and available in literature, were the basis of an instrument devised to analyse chemistry textbooks used in secondary and tertiary education. This paper presents and discusses typical problematic language found in student textbooks in the light of students’ current frameworks of understanding as described in literature.

Natural products from Brazilian biodiversity as a source of new models for medicinal chemistry

Bolzani, Vanderlan da Silva; Valli, Marilia; Pivatto, Marcos; Viegas, Claudio
Fonte: Int Union Pure Applied Chemistry Publicador: Int Union Pure Applied Chemistry
Tipo: Artigo de Revista Científica Formato: 1837-1846
ENG
Relevância na Pesquisa
46.36%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Processo FAPESP: 03/02176-7; Natural products are the inspiration for many valuable therapeutic agents and attest to biodiversity being a rich source of new molecular structures. Their value as templates for medicinal chemistry remains undisputed, even after the growth of the combinatorial chemistry era. Tropical environments, such as Brazilian biomes, offer a particularly rich potential for biologically active compounds with unique structures and continue to contribute toward modern drug discovery. Our bioprospecting of plant species of the Cerrado and Atlantic Forest biomes has yielded promising bioactive secondary metabolites, and we describe some of these molecules and semisynthetic derivatives as potential acetylcholinesterase (AChE) inhibitors.

The physics and chemistry of transport in CdSe quantum dot solids

Jarosz, Mirna, 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 182 p.; 3149934 bytes; 4199144 bytes; application/pdf; application/pdf
ENG
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Semiconductor quantum dots (QDs) have tunable opto-electronic properties and can be chemically synthesized and manipulated with ease, making them a promising novel material for many diverse applications. An understanding of the physics of charge transport in QDs is not only important for realizing QD based electronic devices, but it also provides crucial insight into the chemical and optical properties of QDs. This thesis highlights how photoconductivity measurements are valuable to advancing our understanding of QD physics because they are exquisitely sensitive to the optical, chemical, and electronic properties of QDs. The work presented in this thesis emphasizes how the chemistry and physics of QD films are deeply entwined. Chapter 2 demonstrates that the photoconductivity and dark conductivity of CdSe QD films are enhanced following annealing at high temperatures. Chapter 3 illustrates that the purity of the QD capping reagent (tri-n-octylphosphine) and the methods used for film preparation can each affect the observed photocurrent by two to three orders of magnitude. In Chapter 4, the methods for CdSe film preparation developed in Chapter 3 are used to make films that exhibit photoconductivity properties consistent with having a low density of trapped charges...

Small-molecule activation chemistry catalyzed by proton-coupled electron transfer

Chang, Christopher J., 1974-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 2 v. (343 leaves ); 15717109 bytes; 15716907 bytes; application/pdf; application/pdf
ENG
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Proton-coupled electron transfer (PCET) is the basic mechanism for bioenergetic conversion. Consummate examples include water oxidation in photosynthesis and oxygen reduction in respiration. Despite the importance of PCET in such catalytic bond-making and bond-breaking reactions, the underlying mechanisms of coupled proton and electron transport in these processes is not well understood. To address mechanistic issues surrounding the role of PCET in catalytic chemical transformations, we have begun characterizing PCET events at a molecular level in a broad spectrum of small-molecule activation reactions for the first time. Two distinct structural scaffolds have been elaborated to study the PCET chemistry of 0-0 bond forming and cleaving reactions. The first consists of platforms containing two redox sites linked face-to-face by a rigid xanthene (DPX) or dibenzofuran (DPD) spacer - Pacman porphyrins. A comparative structural study demonstrates that DPD has the unprecedented ability to open and close its binding pocket by a vertical distance of over 4 A upon substrate binding, providing the first direct observation of the Pacman effect in a single cofacial platform. Moreover, efficient oxygen-activation chemistry is preserved when such cofacial motifs exhibit a large range of vertical motion; for example...

The physics and chemistry of semiconductor nanocrystals in sol-gel derived optical microcavities

Chan, Yinthai
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 193 p.
ENG
Relevância na Pesquisa
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The incorporation of semiconductor nanocrystals (NCs) into sol-gel derived matrices presents both novel applications as well as a robust platform in which to investigate the nonlinear optical properties of NCs. This thesis summarizes our present understanding of the chemistry of the incorporation process and the applications and underlying optical physics that was gleaned from studying these NC-doped sol-gel structures. Chapter 2 describes the synthesis of NC-doped core-shell silica microsphere composites of tunable size and emission wavelength, as well as their subsequent use for in-vivo imaging of blood vessels. This chapter illustrates how an appreciation of the kinetics of the Stober process allowed for the achievement of highly monodisperse microsphere composites with a uniform incorporation of NCs. Chapter 3 reviews the requirements for achieving stimulated emission in CdSe NCs and details the development of NC-based lasers through sol-gel derived microcavities, from distributed feedback (DFB) grating structures to spherical microresonators exhibiting whispering-gallery mode lasing. Chapter 4 compares and explicates the differences between silica and titania as host matrices for NCs in terms of their chemical stability in the presence of solvents.; (cont.) This chapter explores the possibility of integrating NC-based microcavity lasers with microfluidic networks...

Quantum chemistry for spectroscopy : a tale of three spins (S = 0, 1/2, and 1)

Wong, Bryan Matthew, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 204 p.
ENG
Relevância na Pesquisa
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Three special topics in the field of molecular spectroscopy are investigated using a variety of computational techniques. First, large-amplitude vibrational motions on ground-state singlet (S0) potential energy surfaces are analyzed for both the acetylene/vinylidene and the HCN/HNC isomerization systems. Electronic properties such as electric dipole moments and nuclear quadrupole coupling constants are used as diagnostic markers of progress along the isomerization path. Second, the topic of electronically excited triplet states and their relevance to doorway-mediated intersystem crossing for acetylene is considered. A new diabatic characterization of the third triplet electronic state, T3, enables a vibrational analysis of data obtained from current and past experiments. The last part of this thesis reviews the techniques and ideas of electron-molecule collisions relevant to Rydberg states of diatomic molecules. Previously developed and current methods of treating the excited Rydberg electron are evaluated and extended. Each of these three topics in molecular spectroscopy is studied using ab initio approaches coupled with experimental observations or chemically intuitive models. The unique combination of quantum chemistry and spectroscopy stimulates further developments in both theory and experiment.; by Bryan Matthew Wong.; Thesis (Ph. D.)--Massachusetts Institute of Technology...

Distal hydrogen-bonding effects and cofacial bimetallic salen architectures for oxygen activation chemistry

Yang, Jenny Yue-fon
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 254 p.
ENG
Relevância na Pesquisa
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Two distinct structural scaffolds elaborated from Schiff-base macrocycles were designed to study the proton-coupled electron transfer chemistry of 0-0 bond forming and activation chemistry. The "Hangman" architecture is composed of hydrogen-bonding functionalities poised over a redox active manganese salophen or salen platform. The complexes proved to be proficient catalase mimics (disproportionation of hydrogen peroxide to water and oxygen). Detailed spectroscopic, computational, and structure-function relationship studies elucidated the key redox, steric, and secondary coordination sphere effects for optimal catalytic ability. The incorporation a chiral backbone into the macrocycle led to catalysts that perform enantioselective epoxidation of unfunctionalized olefins. A macrocycle with an amide, imine, and bisphenolic functionalities was also incorporated as the redox platform in the Hangman framework; the manganese complex also performed catalytic oxygen atom transfer to olefins. The second framework, dubbed "Pacman", is composed of two salen platforms linked cofacially by rigid pillars xanthene or dibenzofuran. A series of bimetallic complexes, including chromium, iron, manganese, cobalt, copper, and zinc were generated. Mossbauer spectroscopy was used in the characterization of the iron salen complexes...

Commodity cluster computing for computational chemistry

Hawick, K.; Grove, D.; Coddington, P.; Buntine, M.
Fonte: Internet Journal of Chemistry Publicador: Internet Journal of Chemistry
Tipo: Artigo de Revista Científica
Publicado em //2000 EN
Relevância na Pesquisa
46.44%
Access to high-performance computing power remains crucial for many computational chemistry problems. Unfortunately, traditional supercomputers or cluster computing solutions from commercial vendors remain very expensive, even for entry level configurations, and are therefore often beyond the reach of many small to medium-sized research groups and universities. Clusters of networked commodity computers provide an alternative computing platform that can offer substantially better price/performance than commercial supercomputers. We have constructed a networked PC cluster, or Beowulf, dedicated to computational chemistry problems using standard ab initio molecular orbital software packages such as Gaussian and GAMESS-US. This paper introduces the concept of Beowulf computing clusters and outlines the requirements for running the ab initio software packages used by computational chemists at the University of Adelaide. We describe the economic and performance trade-offs and design choices made in constructing the Beowulf system, including the choice of processors, networking, storage systems, operating system and job queuing software. Other issues such as throughput, scalability, software support, maintenance, and future trends are also discussed. We present some benchmark results for the Gaussian 98 and GAMESS-US programs...

Educational analysis of the first year chemistry experiment 'Thermodynamics Think-In': an ACELL experiment

Read, Justin Robert; Kable, Scott Henderson
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Artigo de Revista Científica
Publicado em //2007 EN
Relevância na Pesquisa
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This paper describes an educational analysis of a First Year University chemistry practical called ‘Thermodynamics Think-In’. The analysis follows the formalism of the Advancing Chemistry by Enhancing Learning in the Laboratory (ACELL) project, which includes a statement of education objectives, and an analysis of the student learning experience. The practical consists of a suite of ten well-known, short experiments on the general theme of ‘thermodynamics in chemical change’. Pairs of students undertake a specified and graded set of five of these experiments. All experiments require careful observation by both students, followed by discussion between them until a common, mutually-agreed explanation for their observations can be formulated. The pair then discusses their explanation with a demonstrator, who may challenge it, point out flaws, or provide new information. Student surveys were conducted using the ACELL Student Learning Experience instrument. Analysis of the data shows that students enjoy working on the practical, and report it to be a beneficial learning experience that effectively develops their understanding of thermodynamic principles. The practical also fosters significant interest, and through a process of collaboration and cooperation aids the students in further developing their generic thinking skills.; http://www.acell.org/ACELL-Document-Library.cfm?obj_id=87; Justin R. Read and Scott H. Kable; © The Royal Society of Chemistry

Entropy driven chain effects on ligation chemistry

Pahnke, Kai; Brandt, Josef; Gryn'ova, Ganna; Lindner, Peter; Schweins, Ralf; Schmidt, Friedrich Georg; Lederer, Albena; Coote, Michelle L.; Barner-Kowollik, Christopher
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Artigo de Revista Científica Formato: 14 pages
Relevância na Pesquisa
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We report the investigation of fundamental entropic chain effects that enable the tuning of modular ligation chemistry – for example dynamic Diels–Alder (DA) reactions in materials applications – not only classically via the chemistry of the applied reaction sites, but also via the physical and steric properties of the molecules that are being joined. Having a substantial impact on the reaction equilibrium of the reversible ligation chemistry, these effects are important when transferring reactions from small molecule studies to larger or other entropically very dissimilar systems. The effects on the DA equilibrium and thus the temperature dependent degree of debonding (%debond) of different cyclopentadienyl (di-)functional poly(meth-) acrylate backbones (poly(methyl methacrylate), poly(iso-butyl methacrylate), poly(tert-butyl methacrylate), poly(iso-butyl acrylate), poly(n-butyl acrylate), poly(tert-butyl acrylate), poly(methyl acrylate) and poly(isobornyl acrylate)), linked via a difunctional cyanodithioester (CDTE) were examined via high temperature (HT) NMR spectroscopy as well as temperature dependent (TD) SEC measurements. A significant impact of not only chain mass and length with a difference in the degree of debonding of up to 30% for different lengths of macromonomers of the same polymer type but – remarkably – as well the chain stiffness with a difference in bonding degrees of nearly 20% for isomeric poly(butyl acrylates) is found. The results were predicted...

How Learning Styles, Chemistry Attitudes and Experiences, Confidence, and Demographics Correlate with Academic Success in First and Second Year Chemistry Courses

Ilnicki-Stone, Elizabeth
Fonte: Brock University Publicador: Brock University
Relevância na Pesquisa
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At Brock University, the Faculty of Mathematics and Science currently has one of the highest percentages of students on academic probation, with many students reporting the most difficulty with Introductory Chemistry in first year and Organic Chemistry in second year. To identify strategies to improve students' performance and reduce the number of students on academic probation, a multi-year research project was undertaken involving several chemistry courses. Students were asked to complete three questionnaires, and provide consent to obtain their final Chemistry grade from the Registrar's Office. Research began at the end of the 2007-08 academic year with CHEM IPOO, and in the 2008-09 academic year, students in the larger CHEM IF92 Introductory Chemistry course were invited to participate in this research near the beginning of the academic year. Students who went on to take second year Organic and Analytical Chemistry were asked to complete these questionnaires in each second year course. The three questionnaires included the Kolb Learning Styles Inventory (Kolb, 1984) modified to include specific reference to Chemistry in each question, Dalgety, ColI, and Jones' (2002) Chemistry Attitudes and Experiences Questionnaire (CAEQ)...

First-principles density functional theory study of sulfur oxide chemistry on transition metal surfaces; 1st-principles density functional theory study of sulfur oxide chemistry on transition metal surfaces

Lin, Xi, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 310 p.; 9412825 bytes; 9412627 bytes; application/pdf; application/pdf
ENG
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In this thesis, the chemistry of sulfur oxides on transition metals is studied extensively via first-principles density functional theory (DFT) computations, focusing on the chemical reactivity and selectivity in sulfur poisoning chemical processes that address environmental concerns. The systematic approach we establish can be extended to general computational studies of small gas-phase molecules interacting with extended surfaces or finite-size clusters. The thesis starts with a theoretical presentation of modem quantum many-body theory that brings together mean-field theory, DFT, and Green's function quantum Monte Carlo theory. The essence of chemical reactivity theory in the framework of DFT is emphasized. The thesis continues with an extensive survey of the current status of sulfur oxide chemistry and an overall presentation of our computational approaches towards a detailed understanding of chemical reactivity and selectivity. The basic guidelines in chemical reactivity are systematically constructed by computed comprehensive thermodynamic data of surface S, O, SO, SO2, SO3, and S04 species as a function of coverage at low and intermediate temperatures. Under these basic guidelines, experimentally measured surface spectra are interpreted...

Control tools for flow chemistry processing and their application to the synthesis of bromodomain inhibitors

Ingham, Richard Jeremy
Fonte: University of Cambridge; Department of Chemistry; Jesus College Publicador: University of Cambridge; Department of Chemistry; Jesus College
Tipo: Thesis; doctoral; PhD
EN
Relevância na Pesquisa
46.41%
Flow chemistry and continuous processing techniques are now frequently used in synthetic laboratories, taking advantage of the ability to contain reactive or hazardous intermediates and to perform moderate scale-up processes for important compounds. However, only a limited number of methods and tools for connecting flow synthesis steps into a single protocol have been described, and as a result manual interventions are frequently required between consecutive stages. There are two main challenges to overcome. Work-up operations such as solvent extractions and filtrations are invariably needed to ensure high purity of the intermediates. Solutions for achieving this are well established within industrial facilities for continuous production, but adapting such machinery for laboratory use is rarely straightforward. Secondly, the combination of multiple steps tends to result in a more elaborate reactor configuration. The control procedures required to achieve optimum performance may then be beyond the capabilities of a single researcher. Computer control and remote monitoring can help to make such experiments more practical; but commercially-available systems are often highly specialised, and purpose-built at high cost for a particular system...

Biofuels & atmospheric chemistry: what can a global model tell us about our future decisions?

Pike, Rachel Catherine
Fonte: University of Cambridge; Department of Chemistry Publicador: University of Cambridge; Department of Chemistry
Tipo: Thesis; doctoral; PhD
EN
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Biomass energy is the oldest form of energy harnessed by humans. Currently, processed biofuels, which are derived from biomass, are being pursued as a possi- ble route to decarbonize the transport sector?a particularly dif?cult task for both technological and sociological reasons. In this thesis I explore the impacts that large scale biofuel use could have on atmospheric chemistry. I review the current state of biofuels politically and technologically, focusing on ethanol and biodiesel. I discuss the salient features of tropospheric chemistry and in particular the oxidation of isoprene, an important biogenic volatile organic compound. I examine the impact that including isoprene oxidation has in a new chemistry-climate computer model, UKCA; the response of ozone turns out to depend on local chemical conditions. To evaluate the global model, I use data from the OP3 ?eld campaign in Malaysia and compare it with output from the model chemical mechanism. The mechanism is able to reproduce NOx and ozone measurements well, though is more sensitive to representations of physical rather than chemical processes. I also perform a simple sensitivity study which examines crop changes in the region of Southeast Asia. In the ?nal two chapters...

The Quixote project: Collaborative and Open Quantum Chemistry data management in the Internet age

Adams, Sam; de Castro, Pablo; Echenique, Pablo; Estrada, Jorge; Hanwell, Marcus D; Murray-Rust, Peter; Sherwood, Paul; Thomas, Jens; Townsend, Joseph A
Fonte: Murray-Rust group, Unilever Centre for Molecular Science Informatics, Department of Chemistry, University of Cambridge Publicador: Murray-Rust group, Unilever Centre for Molecular Science Informatics, Department of Chemistry, University of Cambridge
Tipo: Article; not applicable
EN
Relevância na Pesquisa
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Computational Quantum Chemistry has developed into a powerful, efficient, reliable and increasingly routine tool for exploring the structure and properties of small to medium sized molecules. Many thousands of calculations are performed every day, some offering results which approach experimental accuracy. However, in contrast to other disciplines, such as crystallography, or bioinformatics, where standard formats and well-known, unified databases exist, this QC data is generally destined to remain locally held in files which are not designed to be machine-readable. Only a very small subset of these results will become accessible to the wider community through publication. In this paper we describe how the Quixote Project is developing the infrastructure required to convert output from a number of different molecular quantum chemistry packages to a common semantically rich, machine-readable format and to build respositories of QC results. Such an infrastructure offers benefits at many levels. The standardised representation of the results will facilitate software interoperability, for example making it easier for analysis tools to take data from different QC packages, and will also help with archival and deposition of results. The repository infrastructure...

Open Data, Open Source and Open Standards in chemistry: The Blue Obelisk five years on

O'Boyle, Noel M.; Guha, Rajarshi; Willighagen, Egon L.; Adams, Samuel E.; Alvarsson, Jonathan; Apodaca, Richard L.; Bradley, Jean-Claude; Filippov, Igor V.; Hanson, Robert M.; Hanwell, Marcus D.; Hutchison, Geoffrey R.; James, Craig A.; Jeliazkova, Nina;
Fonte: Murray-Rust group, Unilever Centre for Molecular Science Informatics, Department of Chemistry, University of Cambridge Publicador: Murray-Rust group, Unilever Centre for Molecular Science Informatics, Department of Chemistry, University of Cambridge
Tipo: Article; not applicable
EN
Relevância na Pesquisa
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Background: The Blue Obelisk movement was established in 2005 as a response to the lack of Open Data, Open Standards and Open Source (ODOSOS) in chemistry. It aims to make it easier to carry out chemistry research by promoting interoperability between chemistry software, encouraging cooperation between Open Source developers, and developing community resources and Open Standards. Results: This contribution looks back on the past 5 years and surveys progress and remaining challenges in the areas of Open Data, Open Standards, and Open Source in chemistry. Conclusions: We show that the Blue Obelisk has been very successful in bringing together researchers and developers with common interests in ODOSOS, leading to development of many useful resources freely available to the chemistry community.; NMOB is supported by a Health Research Board Career Development Fellowship (PD/2009/13). The OSRA project has been funded in whole or in part with federal funds from the National Cancer Institute, National Institutes of Health, under contract HHSN261200800001E. The content of this publication does not necessarily reflect the views of the policies of the Department of Health and Human Services, nor does mention of trade names, commercial products...

Chemistry Add-In for Word

Townsend, Joseph A
Fonte: Murray-Rust group, Unilever Centre for Molecular Science Informatics, Department of Chemistry, University of Cambridge Publicador: Murray-Rust group, Unilever Centre for Molecular Science Informatics, Department of Chemistry, University of Cambridge
Tipo: Other; not applicable
EN
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Poster presented at the VSMF Symposium held at the Unilever Centre on 2011-01-17; The Chemistry Add-In for Word is an Open Source program that allows chemists to create, edit and manipulate chemistry (labels and 2D structures) in the Word environment. the on-screen representation is backed by semantic data in Chemical Markup Language (CML). Combined with domain-aware libraries we enable novel functionality in data checking during the authoring process, chemistry-centric article reading support and data-mining applications. [http://research.microsoft.com/chem4word/] [http://chem4word.codeplex.com/]; The Chem4Word project was sponsored and supported by Microsoft External Research.

The Contributions of James Moir to Physical Chemistry

Loyson,P.
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2014 EN
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James Moir was a pioneering chemist in the early 1900s who played a leading role in various chemical societies in South Africa. Although he was mainly an organic chemist, he was a very good all-round chemist, whose analytical and organic activities have already been covered in this j ournal. This article examines his research in physical chemistry, covering the spectral analysis of the ruby and emerald gemstones, a detailed analysis of part of the Fraunhofer lines of the solar spectrum, and an examination of the spectra of cobalt compounds, the permanganate ion, and uranium compounds. Finally, as part of his inorganic and analytical investigations, he also delved into the physical chemistry aspects of solution chemistry, particularly the hydrolysis of the cyanide ion.

Students' conceptions about the sub-microscopic approach to explanations in chemistry throughout their BSc degree course

Serobatse,Boingotlo M; Selvaratnam,Mailoo; Drummond,Helen P.
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2014 EN
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The main objective of this study was to test chemistry students' competence, throughout the entire BSc course at North-West University (Mafikeng Campus), in the use of the important and widely applicable strategy of explaining the facts, principles and laws of chemistry in terms of the properties of the constituent sub-microscopic particles. Seventeen questions were used for systematically testing all basic aspects of chemistry. The aspects tested included the following: the types of particles present and their properties in various types of matter (e.g. metals, non-metals, ionic compounds, covalent compounds, mixtures, gases, liquids, solids, solutions); the changes in the nature, arrangement and properties of the particles during both physical and chemical changes; the explanation of physical and chemical properties of substances in terms of the properties of the constituent particles. Student performance was consistently bad and it did not improve as they progressed from year to year in their BSc course. More than half of them (average performance in all questions) had difficulty in answering the questions. Analysis of students' answers suggested that most students' difficulties were due to their not identifying clearly the problem that had to be solved and their not using the relevant principles and reasoning to solve the problems. Instead...

Grade 12 achievement rating scales in the new National Senior Certificate as indication of preparedness for tertiary chemistry

Potgieter,Marietjie; Davidowitz,Bette
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 EN
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There has been much discussion on the impact of the new curricula for Grades 10-12 on the preparedness for tertiary studies of the 2009 cohort in subjects such as mathematics, chemistry and physics. Using the Chemical Competence Test that was developed and refined earlier, we have evaluated the proficiencies of incoming students to determine the shifts in preparedness for tertiary chemistry that occurred after students wrote the National Senior Certificate (NSC) in South Africa for the first time in 2008. Data were collected in 2009 for first-time entering students at the Universities of Pretoria (UP) (N = 828) and Cape Town (UCT) (N = 315) and compared with that of students who were educated according to the former National Education curriculum (NATED 550) (2005: N UP+UCT = 776). The raw score results showed a decline in proficiency in all topics, and significantly reduced skills development, with mastery of acids and bases showing the most serious decline. Rasch analysis of the data indicated that a 12 percentage point shift in preparedness occurred in 2009 compared with 2005. The contribution to this shift of a mismatch between the new NSC rating scale and the one used previously was also investigated. The implications of the findings for selection and placement and teaching of first year chemistry courses are discussed.