Volume 15, Issue 3  (2006)

Editorial:
D. Lazarov. Why We Teach Untruths	163
Full text: PDF (114 KB)
News:
List of Textbooks for 2006/2007 School Year	171
Prospective Chemistry Students for 2006/2007 School Year	172
Ts. Zahariev. 200th Anniversary of Thomas Graham (1805-1869)	173
Letters to the Editor:
M. Shamsi. New Way to Aware Students with Safety Rules	177
Teaching Efficiency:
M. Das Sharma. Chemistry Riddle - A New Approach to Innovative Teaching	179
Teaching Chemical Experiment:
R. Katenaire. Towards a More Predictable Thin Mercury Film Behaviour	187
Problems:
M. Atanassova, I. Dukov. Some Cases of Balancing of Oxidation-Reduction Reactions Using the Oxidation-Number Method	192
Advanced Chemistry for Teachers:
M. Nedyalkov. Nature, Control and Application of the Phenomenon of Wetting	198
From the Research Laboratories:
A. Semnani, H.R. Pouretedal, A. Firooz, M.H. Keshavarz. Interaction between 1,4,7-Trimethyl-1,4,7-Triazacyclononane with Bromine, DDQ, TCNQ, TCNE and Bromanil in Chloroform Solution	220
Archives:
P.R. Bontchev. Establishment and Development of the Department of Analytical Chemistry: A Coincise Review	231
Khimiya, Volume 15, Issue 3 (2006) Khimiya. 15, 179-186 (2006): Abstract. Riddles in chemistry can bring about a paradigm shift in chemistry teaching. My experience with a large number of students in recent years is that they take the challenge in solving the riddle, enjoy the fun and satisfaction in arriving at the solution and teachers can assess their analytical ability more accurately. Keywords: chemistry riddle; innovative teaching References: 6 top Khimiya. 15, 187-191 (2006): Abstract. The paper proposes a new approach to mercury film formation on a carbosital substrate. The experimental variables such as mercury and electrolyte concentration, the deposition potential and time are investigated and optimized. The thin mercury film is highly reproducible and so are the metrological characteristics whose standard deviation is in the 0.02 – 0.05 range. Keywords: Mercury film; Carbosital; Reproducibility References: 14 top Khimiya. 15, 192-197 (2006): Abstract. Some more complicated examples when balancing oxidation-reduction equations are listed in the paper. Keywords: oxidation number, oxidation-reduction reactions, oxidation-number method References: 6 top Khimiya, 15, 198-219 (2006): Abstract. A synthesized account on some experimental methods for investigation of black foam films is presented. Using elementary notions the main film’s properties are defined. It is shown that many of these important parameters of the films can be measured using a universal measuring cell. For the different methods used, the manipulations with this cell are explained in details. For illustration, some main experimental results, obtained with these methods and using this technique, are exhibited.  Keywords: Thin Liquid Films; Foam Black Films; Film Tension; Film Contact Angle; Line Tension. References: 22 top Khimiya, 15, 220-230 (2006): Abstract. The interaction between 1,4,7-trimethyl-1,4,7-triazacyclononane (TMTACN) as n-donor with bromine as s-acceptor and TCNE, DDQ, TCNQ and bromanil as p-acceptors has studied spectrophotometrically in chloroform solution at 25oC. The results of bromine are indicative of the formation of complex [TMTACNBr+Br3-] through equilibrium reaction. In the case of TCNE, DDQ and bromanil 1:3, 1:2 and 1:1 TMTACN to p-acceptor adducts through equilibrium reactions are confirmed, respectively. The stability constant of bromanil complex is obtained by Hildebrand method. The computer fitting of absorbance-mole ratio data determines the other stability constants. Finally, TCNQ forms TCNQ.- radical anion and 7-TMTACN-7,8,8-tricaynoquinodimethane through two simultaneous equilibrium reactions. In all cases the spectral changes upon addition of donor are discussed. Keywords: Spectrophotometry, 1,4,7-Trimethyl-1,4,7-triazacyclononane, Bromine, Bromanil, DDQ, TCNQ, TCNE, Charge-transfer   References: 25 top