The Efficacy of Problem-based Learning in an Analytical Laboratory Course for Pre-service Chemistry Teachers

Chemistry students; Creative thinking ability; Problem-based learning; Self-evaluation; Self-regulated learning skill

Solid-state 1H and29Si NMR studies of silicate and borosilicate gel to glass conversion

Silicate and borosilicate gels were prepared by the sol-gel process and thermally treated in the 150-850°C temperature range. Solid-state 1H MAS and 29Si CP/MAS NMR spectroscopy were used to investigate the effects of heat treatments on the silicate gel to glass conversion process. The 1H NMR Isotropic chemical shifts and the relative intensities of hydrogen bonded and isolated silanol groups have been used to access the information concerning the dehydration process on the silicate gel surface. The 29Si NMR isotropic chemical shifts affected by the local silicon environment have been used to determine the degree of crosslinking, i.e. the number of siloxane bonds. These NMR results suggest that the silicate gel to glass conversion process is occurred by two stages which are dependent on the temperature; (1) the formation of particles up to 450°C and (2) the formation of large particles by aggregation of each separated single particle above 450°C. In addition, the effects of B atom on the formation of borosiloxane bonds in borosilicates have been discussed

A study on the understanding about nature of scientific knowledge and attitude toward scientific inquiry of pre-service science teacher through open inquiry

The purpose of this study is to investigate the understanding of nature of scientific knowledge and attitudes toward scientific inquiry of pre-service science teachers experienced open inquiry. The study was conducted in 10 sessions of open inquiry-based chemistry experiment. The subjects were 40 pre-service science teachers recruited from the experiment class. They received pre-test, mid-test, post-test on understanding nature of scientific knowledge and attitudes toward scientific inquiry of open inquiry activities. 20 pre-service science teachers among them participated in the interview. The results of this study are as follows. First, there was a significant difference in pre-service science teachers’ understanding of the nature of the scientific knowledge (p<.05). In particular, understanding of creativity and sociality parts improved gradually. Second, pre-service science teachers’ attitude toward scientific inquiry had changed negatively until the middle of the semester, and then changed positively later. The post-test score was significantly higher than the mid-test score (p<.05)

Single-crystal Al-27 NMR study of corundum alpha-Al2O3

Al-27 NMR chemical shielding, quadrupolar coupling, and dipolar coupling interactions for corundum (alpha-Al2O3) are determined from the single-crystal Al-27 NMR spectra according to the rotation about three orthogonal axis. Al-27 NMR parameters obtained in this work with high accuracy are as follows: delta(iso) = 7.4(4) ppm, QCC = 2.30(4) MHz, eta = 0.08(3), and R = 2.0(3) kHz. This work appears to be the first NMR measurement of an aluminum-aluminum dipolar coupling interaction in alpha-Al2O3 crystals

11B NMR of boron-doped graphite as the negative electrode of a lithium secondary battery

Boron-doped graphite used as a negative electrode for a lithium rechargeable battery is known to have higher discharge capacity than undoped graphite. Herein, the graphites were mixed with 1, 2.5, 5, and 7 wt.% of boron carbide during the graphitizing process. The structural states of boron in those boron-doped graphites were successfully identified by solid-state 11B NMR spectroscopy. For 1 wt.% sample, all boron atoms were at substitutional sites, as evident by the second-order quadrupole broadened 11B NMR line having a quadrupole coupling constant, QCC=3.36(2) MHz. The NMR results show evidence of excess boron atoms recrystallizing as boron carbide during the graphitizing process which is in agreement with XRD data. Agreement of experimental results with computer simulated data indicate that the substitutional sites in boron-doped graphites were observed for the first time. © 2002 Elsevier Science Ltd. All rights reserved

Second-year college students’ scientific attitudes and creative thinking ability: Influence of a problem-based learning (PBL) chemistry laboratory course

This research examined the effects of a problem-based learning (PBL) chemistry laboratory course for second-year college students (N1/4 20) on students' scientific attitudes with an emphasis on their creative thinking abilities. The findings were contrasted with a traditional laboratory course (N1/4 26) to elucidate any differences in the influence of the courses. Only female students participated in the study which was conducted in a private university for women in Korea. A 20-item Scientific Attitudes Questionnaire administered to both groups as a pretest and a posttest revealed that there were significant changes in criticism, cooperativeness, and creativity at the end of instruction only among students in the PBL course. The posttest scores of the Torrance Tests of Creative Thinking to gauge students' creative thinking ability were significantly higher for the students in the PBL course on all three dimensions. The research suggests that PBL laboratory courses in chemistry have great potential to positively change students' scientific attitudes towards learning chemistry and enhance their creative thinking abilities. © Springer-Verlag Berlin Heidelberg 2015

Solid-State 87Rb NMR study in powdered RbMnCl3

Structural phase transition at 290 K and the implication on the intermediate phase above 290 K in powdered RbMnCl3 are observed by using a solid-state 87Rb NMR spectroscopy. Quadrupole coupling constants (e2qQ/h), the asymmetry parameters (η), and the relative peak intensities for two physically nonequivalent Rb sites, Rb(I) and Rb(II), are determined from nonlinear least-squares fits to the 87Rb NMR powder patterns in the temperature range from 260 to 330 K. Quadrupole coupling constants and the asymmetry parameters are examined for the detection of the phase transition resulting in a significant structural change in the Rb(II) site. In addition, changes in the relative peak intensity between the Rb(I) and Rb(II) sites seem to suggest the existence of an anomalous intermediate phase, which is complemented by the differential scanning calorimetry and X-ray diffraction studies. © 2000 Academic Press

Solid-state 31P NMR chemical shielding tensors in binuclear platinum diphosphite complexes

The principal elements of the 31P NMR chemical shielding tensors have been determined for three binuclear platinum diphosphite complexes, K4[Pt2(P2O5H2) 4]·2H2O ("Pt2"), K4[Pt2(P2O5H2) 4Cl2]·2H2O ("Pt2Cl2"), and K4[Pt2(P2O5H2) 4Br2]·2H2O ("Pt2Br2"), by using a Herzfeld-Berger graphical method for interpreting the 31P MAS spectrum. The orientations of 31P chemical shielding tensor relative to the molecular axis system are partially assigned with combination of the longitudinal relaxation study of HPO3 2- and the reference to known tensor orientations of related sites; the most chemical shielding component, δ33, is directed along the P-Pt bond axis. A discussion is given in which the experimental principal elements of the 31P chemical shielding tensor are related with the Pt-Pt bond distances in binuclear platinum diphosphite complexes

Molecular conformation of hydrogen-bonded ethylene glycol in sodalite: A 1H CRAMPS NMR, IR, and 2H NMR study

Analysis of the variable-temperature 1H CRAMPS NMR, IR, and 2H NMR spectra obtained from the ethylene glycol molecules in two sodalite materials with Si/Al ratios of ∞ and ca. 5 reveals that the intermolecular hydrogen bonds between the framework oxygens and the OH groups of the guest molecule, which appear only in the isomorphously Al-substituted zeolite, are preserved even at 200 °C, which is higher than the crystallization temperature (175 °C) of the zeolite host. As a consequence, the conformations of the encapsulated ethylene glycol molecules in these two materials were found to maintain in a manner distinctly different from each other over the temperature range (25-200 °C) studied here

Analysis of the quadrupolar coupling effect on the line intensities using single-crystal nutation NMR in alpha-Al2O3 crystals

With ID-nutation NMR for a spin I = 5/2 system, the relative line intensities of the central and the inner- and outer-satellite transitions are calculated as functions of quadrupolar coupling omega(Q) and rf pulse strength omega(rf). Experimentally measured line intensities including both central and satellites are used to extract the values of ou and omega(rf) from nonlinear least-squares fits. The method is illustrated in alpha-Al2O3 crystals (ruby and corundum) with the single-crystal Al-27 nutation NMR spectra. As a result, the new feature that the rf pulse strength shows reduced effect on the satellite transition lines according to the quadrupolar coupling is discussed by using a fictitious spin-1/2 operator