Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Abstract Chemistry for first year students has been identified by Tshwane University of Technology as one of the subjects with a low pass rate. It is apparent that students often memorize formulae and definitions, without understanding the underlying concepts required to work with abstract units of measure. We have found that the majority of students at this university are unable to balance reaction equations satisfactorily. They are also unable to predict the reaction yield, or identify limiting reagents. It is imperative that these and other related problems are overcome before any meaningful change to the high failure rate at first year level will be realized. All conventional forms of lecture presentation failed to make any significant impact on the success rate. Structured worksheets were developed and used, together with tactile models, to address the problems and the initial findings showed a marked improvement. It was discovered that the students’ problems originated from their inability to understand the meaning of subscripts and coefficients in chemical equations. The worksheets and the impact they have made on the students’ understanding of stoichiometry are shared in this paper.

Thesis (Ph. D.)--Rutgers University, 2007. / "Graduate Program in Oceanography." Includes bibliographical references (p. 142-146).

The oxidative coupling of 2,6-di-t-butylphenol under mild reaction conditions is well documented and the subject of many patents. However, the coupling of other monoand di- substituted phenols is not as well documented and thus there is scope for further investigation for providing a convenient, environmentally friendly and economically viable method for the oxidative coupling of these phenols. In this study, the oxidative coupling of a variety of alkylated phenolic substrates, 2-tbutylphenol, 2,6-di-t-butylphenol, 2,4 -di-t-butylphenol and ,4-dimethylphenol, using a range of different oxidizing agents, were investigated by means of experimental and/or theoretical means. The dibutylated aromatics provided the highest selectivities to their respective coupled products, with results obtained with the dimethyl analogue being only satisfactory, and that for 2 -t-butylphenol being totally inefficient. PM3 Molecular orbital (MO) calculations were used to predict the possible modes of coupling for the substrates 2,6 -di-t-butylphenol and 2,4-di-t-butylphenol, and these results were then compared with those obtained experimentally in the laboratory. Preliminarily, the coupling of unsubstituted phenolics was also assessed by means of MO calculations. Much emphasis was placed on Ce(IV) as the oxidant, and the reaction conditions under which it was used and the results that were obtained have not been reported before and are therefore novel. The oxidation of 2,4-di-t-butylphenol using Ce(IV) in the presence of methanesulphonic acid was optimized to afford high yields and selectivities to the desired ortho C-ortho C coupled product under mild reaction conditions. Various reaction parameters were also investigated in this case, such as varying the MeSO3H concentration, the solvent, the reaction temperature, the reaction time, the substrate loading, the rate of oxidant addition and the substrate to oxidant ratio. Ce(IV) also gave a high selectivity to the para C-para C coupled product when IX using 2,6-di-t-butylphenol as the substrate. However, it was not as effective with 2,4- dimethylphenol, and even less so with 2-t-butylphenol. The oxidation reactions of 2-t-butylphenol and 2,4-dimethylphenol with various coupling agents were also investigated with the intention of obtaining high selectivities to the respective desired coupled products. In these studies, 2-t-butylphenol afforded a large number of products, irrespective of the oxidant used. The dimethyl analogue was more selective, but results were not optimal. It was clear that the number of substituents on the phenol ring, their nature and their position with regards to the hydroxyl moiety was of great importance and made a significant impact on the preferred coupling mode of the substrate. It was observed that steric effects also played a major role in the outcome of these reactions: 2,6-di-t-butylphenol never afforded any C-O coupled products whereas 2-t-butylphenol, 2,4-di-t-butylphenol and 2,4-dimethylphenol all appeared to undergo some C-O coupling. Finally, reaction mechanisms were provided for both the K3Fe(CN)6 and Ce(IV) work, these reacting in basic and acidic media, respectively. It was proposed that both of these mechanisms operate through the initial formation of the phenoxyl radical.

No description available.

A research report in partial fulfillment of the award of Master of Science (MSc.) in Science Education submitted to the Faculty of Science, School of Education, University of the Witwatersrand, Johannesburg, South Africa, 2017 / Professional learning communities are generally regarded as having a positive impact in improving and developing teacher knowledge. Literature has shown that group planning and professional learning communities have an impact on the quality of teaching and subsequent improvement in learner performance. Practicing teachers, preservice teachers, education authorities, curriculum advisors and teacher educators all thrive to find out about the kind of teaching that brings about effective learning inside classrooms, the most appropriate approach to improve teaching and learning in class, and in particular, science classes, remains vague, though. This study examines how teacher knowledge is developed in the context of a lesson study within a specific concept of the topic stoichiometry: the ‘mole’. The case of three practicing science teachers is considered through the observation of their interactions with teacher educators during the five (5) weeks in which the participant teachers planned, taught and reflected on the mole concept together with science teacher educators and science teacher education specialists. A pretest is administered to the participant teachers at the beginning of the study; this is followed by intervention discussions based on the concept of the mole. Each of the participants then teaches the lesson to 11th grade learners in their school, each lesson is reflected upon and an iterative cycle of teaching and re-teaching the concept describes the lesson study approach used in this study. At the end of the intervention, a post-test is administered to the three participant teachers. The analysis and description of the teachers’ responses to structured test items before and after the topic specific intervention and verbal contributions during meetings are sources of qualitative data in this study. The qualitative data about topic specific pedagogy and the interaction of TSPCK components obtained in this study is used as evidence to show that topic-specific interventions assist teachers in developing pedagogical content knowledge in science education. / MT 2019

For the theory of electrochemical analysis, a kinetic model that considers the ion transport limitations near the cathode of electrode is based upon a generalized Butler-Volmer equation and has been modified in theory and developed. The subjects of this study are the investigation of the kinetics mechanism of CdTe electrodeposition from an aqueous solution containing CdSO4, TeO2, and H2SO4 in cyclic voltammetry and applied to the optimal control of the composition and stoichiometric deviation of CdTe thin film by electrodeposition. The computer simulation is performed to understand the influences of electrodeposited parameters in the process, such as deposition temperature, pH value and concentrations of Cd2+ and HTeO2+ ions, is one of the focuses in this study. In this investigation, a novel electrochemical method for simultaneously measuring diffusion coefficient and ion transference number is applied in the simulation of CdTe electrodeposition for the first time. From the fitting of the experimental data, the values of the thermodynamic, kinetic and mass transport parameters of the electrodeposition process are obtained. In addition, the modified Butler-Volmer model predicts the potential of perfect stoichiometry (PPS) for electrodeposition of CdTe thin film, and a good agreement has been found between the calculated and experimental results. It also predicts the composition of electrodeposits for the electrodeposition of CdTe and other II-VI and III-V compounds from solutions containing reducible ions. Furthermore, the one that is worth mentioning in this investigation, a novel algorithm of stoichiometric deviation is also developed and applied to the electrodeposition for the first time. With the change of the parameter, the deviation of stoichiometry can be estimated accurately. The simulated results of mathematical model are verified experimentally using electrodeposition and can obtain two aspects. They are the accurate potential perfect stoichiometry (PPS) in which the intrinsic CdTe thin film can be electrodeposited and the stoichiometric deviation which can be dominated accurately in the adjustment of electrodeposited potential. Besides, the native non-degenerate p-type and n-type CdTe thin film can also be deposited. At PPS, well-connected granular CdTe thin films can be deposited and are predicted to be intrinsic, but are slightly p-type due to cadmium vacancies (VCd). The conversion of conductive type occurs only by defect redistribution and local defect reactions after annealing; the converted n-type layer shows lower resistivity and higher mobility. A film annealed at 350oC exhibits excellent crystallization.

No description available.

No description available.

Ecological stoichiometry is the study of the balance of chemical substances in ecosystems. In freshwaters, research has focused on how the ratios of carbon, nitrogen and phosphorus in organisms and their environment affect ecosystem processes. Because autotrophs have variable stoichiometry, particulate C:N:P ratios are used to assess nutrient availability in lakes. Zooplankton have relatively fixed stoichiometry and so differences between their body stoichiometry and the stoichiometry of their food can constrain their growth. Ecological stoichiometry predicts that zooplankton with low C:P body ratios (e.g., Daphnia) will be limited by the P content of their food in lakes where seston C:P is high. The stoichiometric theory of consumer-driven nutrient recycling (CNR) predicts that the stoichiometry of a consumer will influence the stoichiometry of the nutrients they regenerate through such processes as egestion and excretion. In lakes, zooplankton with a low body N:P are expected to regenerate nutrients in a high N:P ratio, potentially shifting nutrient limitation of the food web from N to P limitation. I used data from 99 Canadian lakes to test the following: a. Are particulate C:P and N:P ratios consistent with other P deficiency indicators? b. Do seston C:P and N:P ratios affect zooplankton community composition? c. Does zooplankton community composition affect plankton P limitation as predicted by CNR? Particulate C:P and N:P ratios generally agreed with other P deficiency indicators, except dissolved phosphate turnover times (TTPO4). C:P and N:P suggested P sufficiency more often than TTPO4, possibly because these two indicators respond to P deficiency over different time scales. Most zooplankton biomass parameters were negatively related to seston C:P ratios consistent with improved food quality at lower seston C:P. There was, however, no evidence that Daphnia were more strongly affected than any other zooplankton. Turnover times of particulate P in the whole plankton assemblage were not related to zooplankton community structure parameters. However, particulate P turnover in the >200 µm size fraction increased with increasing zooplankton biomass. There was no evidence for a particular effect of Daphnia on particulate P turnover. Phosphorus deficiency indicators showed a trend of relaxing P deficiency as zooplankton biomass and the proportion of Daphnia increased. This contradicts the predictions of CNR which suggest that Daphnia should cause greater P deficiency in lakes.