Acid-basic properties of chromium(III) oxide surface

The article is devoted to the study of the nature and number of acid-base centers on the surface of chromium(III) oxide obtained by precipitation from an aqueous nitrate solution. The curve of the distribution of the number of acidbase centers of the samples is plotted depending on the indicator of the ionization constant of indicators. It was determined that the main Lewis centers make the main contribution to the acidity of the samples; there are also Bronsted centers of different acidity. A comparative analysis of the structural features of the surface of oxides of chromium, zinc and binary systems Cr (III)–Zn (II) was carried out according to the results of X-ray phase analysis of oxides and thermolysis of the corresponding hydroxides. Based on this, the possibility of obtaining nanosized catalysts based on oxide-hydroxide systems of chromium with a number of 3d-metals obtained in the process of polynuclear hydroxocomplexation is predicted.

Residue Analysis of Oxytetracycline in Milk Sample by Two Different Chromatographic Methods and Determination of Ionization Constant Values

In the present study, two analytical methods for the residue analysis of oxytetracycline in milk sample have been generated. In HPLC method, the analysis was performed on an X Terra RP-18 column at 25 °C with the mobile phase as methanol: water (20 : 80 )(v/v) modified to pH 5. For the second method capillary electrophoresis system was used. The analysis of oxytetracycline in milk sample could be achieved without using organic modifier in a 58 cm length capillary at a working voltage of 12 kV with 20 mM NaH2PO4-H3PO4 (pH 7) by capillary electrophoresis. Tetracycline was used as internal standard in both methods. The results calculated from both methods were compared to each other. The calculated data for drugs was checked with the data predicted by the SPARC on-line pKa estimator.

Distribution of ammonia, mono-, di- and triethylamine in the water solution–gas phase system.

The equilibrium distribution of ammonia, ethylamine, diethylamine and triethylamine between their aqueous solutions and the gas phase at 25 ± 0.1 °C have been investigated under equilibrium conditions. Based on the results obtained (using the equations of Henry’s law and the ionization constant), Henry’s constants for these substances have been calculated with the consideration of their interaction with water. It was established that Henry’s law is valid, at least, in the range of amine concentrations in the air 0–200 mg/m3.

Analisis Prior Knowledge Konsep Asam Basa Siswa Kelas XI SMA untuk Merancang Modul Kimia Berbasis REACT

This study is a define phase of 4D model used in Research and Development (R&D) that aims to explore initial concept of grade XI students on acid-base topic before studying the material. Instrument used in this study was a two-tiered diagnostic test in the form of multiple-choice questions with choice of reasons that consisted of 16 items. The test was given to 100 grade XI students from various schools in West Sumatra. Students� answers were processed by grouping them into 3 categories: understand, have misconceptions and do not understand. Data were then analyzed descriptively by calculating the percentage of students' learning difficulties in all of competency achievement indicators that had been compiled. The results showed that students had difficulty in understanding some concepts of acid base such as acid base theory of Arrhenius (75.2%), of Bronsted-Lowry (81.43%), and of Lewis (100%); pH (94.04%); and acid base ionization constant (97.33%). Results of this research are then used as a consideration in the development of acid-base module designed for grade XI Senior High School learning.