#### Letters to the Editor

### The Calendar: Old Style and New One [In Bulgarian]

A. Paskalev

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### Beekeeping Club at School [In Bulgarian]

Z. Garova

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### Differential Teaching in School Science Education: Conceptual Principles

**Abstract. ** School reflects needs of society which change in the course of time. Therefore, a new shaping of both teaching and bringing up of individuality should be realized. Conceptual approach strengthens necessity of essential perfection of content and meaning of the differential teaching.

Keywords: differentiation, content of school chemical education, pedagogical conception, integration, humanization, reflection

G. Yuzbasheva

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### Kinetic Theory of the Ideal Gas: Derivation of the Law of Maxwell and Barometric Formula from the Kinetic Equation of Boltzmann [In Bulgarian]

**Abstract. ** The rigorous theory of ideal gas leads to the Boltzmann kinetic equation. For a system in thermodynamic equilibrium, with no external field, this equation transforms into the Maxwell velocity distribution law for the gas molecules. Is this law holds for a system with gravity? It is true but then the density of the gas is not a constant as it is without gravity; thus the barometric formula is obtained. The kinetic equation of Boltzmann provides an opportunity to derive in a correct manner both of these equations. However, this approach is seldom used in teaching practice.

Keywords: Boltzmannâ€™s kinetic equation, Maxwellâ€™s law, barometric formula

B.V. Toshev

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### Study of Pupils’ Performances (Sixth Grade) on Section „Substances and Their Properties“ in the Subject „Man and Nature“ [In Bulgarian]

**Abstract. ** This article presents the results from assessing studentsâ€™ performances in â€œMan & Natureâ€ (6th grade), in the part related to substances and their transformations. The study was conducted with 1010 sixth graders from various schools on the territory of Lovech region, Bulgaria. The main objective of the paper is to determine to what extent studentsâ€™ performances meet agreed deliverables in the curriculum. Studentsâ€™ performances are evaluated with test established in accordance with state educational requirements and the curriculum for the sixth grade. Specific conclusions have been drawn from the obtained results with respect to studentsâ€™ performances, and some weak points in early science education have been identified.

Keywords: chemistry education, educational standards, achievement test, assessment

I. Burovska, S. Tsakovski

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### Interaction of Iron with Nitric Acid: A Complex Redox Reaction [In Bulgarian]

**Abstract. ** The interaction of Fe with HNO3 of various concentrations causes the production of several products result of HNO3 reduction. Thatâ€™s why the reaction depends on several independent parameters and can be balanced with unlimited sets of non integer stoichiometric coefficients. Besides, this reaction can be represented as a sum of reactions including one of the products of the acid reduction. Such approach also permits to obtain unlimited sets of non integer stoichiometric coefficients by multiplication one or more of the simple equations by random multiplier and following summation.

Keywords: complex redox reactions, stoichiometry, mechanisms

A. Zahariev

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### Theoretical Investigation on the Choice of Independent Parameters for Redox Reactions Balancing with More Than one Degree of Freedom [In Bulgarian]

**Abstract. ** An algorithm and program permitting to balance redox reactions with arbitrary number of degrees of freedom and determination of positive values of the coefficients of linear combination of independent parameters are proposed. This approach gives possibility to determine unlimited sets stoichiometric coefficients for each positive value of the independent parameters without limited conditions. The algorithm is applied for balancing of two redox reactions with two degrees of freedom.

Keywords: material balance method, redox reactions, degrees of freedom, independent parameters, domain of positive independent parameters

S. Petkova, M. Atanassova, R. Chukleva

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### Psychosocial Environment of Chemistry Laboratory Classrooms in Iranian High Schools

**Abstract. ** This study investigates the learning environment of chemistry laboratory classrooms in Iranian high schools. Science Laboratory Environment Inventory (SLEI) was carefully translated into Persian and administered to 748 (M= 325 and F=423) Iranian high school students. Data analyses attested to the sound factorial validity and internal consistency reliability of the Persian version of SLEI. Comparison of Iranian high school studentsâ€™ scores on actual and preferred forms of the questionnaire revealed that students were not satisfied and preferred a more positive chemistry laboratory environment on all scales. Furthermore, this study proposes some measures that could be taken to improve high school chemistry laboratory classrooms environments. The results will be of significance for chemistry educators to create more efficient and learner-centered chemistry laboratory classrooms environments. The work is distinctive since it is the first learning environment study delving through chemistry laboratory classrooms in Iran.

Keywords: learning environments research, Science Laboratory Environment Inventory (SLEI), Iranian chemistry laboratory classrooms, satisfaction

Z. Eskandari, Nabi.A Ebrahimi

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### Density Functional Theory on the Efficiencies of 2-Phenylimidazo[1,2-a]pyridine and 2-(m-Methoxyphenyl)imidazo[1,2-a]pyrimidine as Corrosion Inhibitors for Mild Steel

**Abstract. ** Density Functional Theory (DFT) method was used to study the corrosion inhibition characteristics of 2-phenylimidazo[1,2-a]pyridine (2PIP) and 2-(m-methoxyphenyl)imidazo[1,2-a]pyrimidine (2MPIP) on mild steel. Quantum chemical parameters such as highest occupied molecular orbital energy (EHOMO), lowest unoccupied molecular orbital energy (ELUMO), the energy gap, chemical hardness, softness, dipole moment, absolute electronegativity, electrophilicity index and the fraction of electron transferred were calculated and correlated to inhibition efficiency of the studied molecules. Low energy band gaps coupled with structural stabilities should favour the adsorption of protonated molecules on metal surface at low concentrations and before the adsorption equilibrium. However, at high concentrations and towards equilibrium desorption of the protonated would be rapid due charge repulsion and molecular distortion from planarity which would facilitate the adsorption of neutral molecules on metal surface at equilibrium.

Keywords: 2-phenylimidazo[1,2-a]pyridine, 2-(m-methoxyphenyl) imidazo[1,2-a]pyrimidine, corrosion inhibitors, molecular indices, protonation, DFT

Banjo Semire, Ayobami Olusegun Odunola

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### Teaching Social Sciences in the Bulgarian Schools for Girls: Morality (1897) [In Bulgarian]

B.V. Toshev

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### History and Philosophy of Science: Some Recent Periodicals (2013)

B.V. Toshev

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### 45th National Conference of Teachers in Chemistry [In Bulgarian]

A. Tafrova-Grigorova

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