Chemistry Journal of Moldova

2011 Volume 6, no.1

TO THE EQUILIBRIUM MODEL CHOICE IN HETEROGENEOUS AQUEOUS SYSTEMS. 1. THEORETICAL BASIS IN THE CASE OF TWO COEXISTING SOLID PHASES

Author(s):

I. Povar, Nina Timbaliuc, Tatiana Cazac, Diana Shepel, Oxana Spinu and Ludmila Chiriac


Field: Analytical chemistry
Type: Research paper
Issue: 2011 Volume 6, no.1
Pages: 57-61
Keywords: equilibrium model, heterogeneous system, solubility product, pH value, solid phase.
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Abstract (JPEG)

DOI: dx.doi.org/10.19261/cjm.2011.06(1).11

Graphical Abstract:
An approach has been developed to determine the equilibrium model in heterogeneous aqueous systems containing a mixture of solid phases from the initial composition of the heterogeneous mixture and the equilibrium values of the pH. This approach allows to significantly reduce the quantity of measured data, properly for solubility measurements. By using the new deduced equations it is possible to determine the solubility products of precipitates on the basis of the known composition of initial mixtures and pH values of saturated solutions avoiding some difficult experimental solubility measurements. The derived relations are useful for solving both direct and indirect equilibrium problems.

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THE INFLUENCE OF THIOSEMICARBAZONE 2,3-DIHYDROXYBENZALDEHYDE ON CATALYTIC CURRENTS IN THE SYSTEM MOLYBDENUM (VI) – POTASSIUM CHLORATE IN ACID SULFATE SOLUTIONS

Author(s):

Ludmila Chiriac, Tatiana Cazac, I. Povar and M. Revenco


Field: Analytical chemistry
Type: Research paper
Issue: 2011 Volume 6, no.1
Pages: 52-56
Keywords: voltammetry, catalytic current, molybdenum, thiosemicarbazone 2,3-dihydroxybenzaldehyde, chlorate of potassium.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2011.06(1).12

Graphical Abstract:
The polarographic catalytic current in acid solutions of Mo(VI), thiosemicarbazone 2,3-dihydroxybenzaldehyde (TSC 2,3-DHBA) and chlorate ions has been investigated. The scheme of reactions, taking place in the solutions and on the electrode, has been proposed. The increase of the catalytic current is explained by the formation of an active intermediate complex [Mo(V)×TSC 2,3-DHBA (ClO-3)]. The rate constant of this complex formation K = 2.56 × 106 mol-1×dm3×s-1, the activation energy Ea = 15.9 kcal×mol-1 and the reaction activation entropy ∆Sa¹ = -23.5 e.u. have been calculated.

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VOLTAMMETRIC BEHAVIOR OF SOME STEELS IN AQUEOUS SOLUTIONS OF HNO3

Author(s):

Gheorghe Nemtoi, Liliana Airinei, Tudor Lupascu and Alexandru Cecal


Field: Analytical chemistry
Type: Research paper
Issue: 2011 Volume 6, no.1
Pages: 45-51
Keywords: corrosion, electrochemical parameters, nitric acid, steels, voltammograms.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2011.06(1).13

Graphical Abstract:
The corrosion process of some steels immersed in HNO3 solutions of different concentrations by means of voltammetric measurements was investigated. For different values of the corrosion potential, or of the contact time: solid steel-aggressive medium, several equations of the type: I = f (E) were proposed, only for linear domains of the voltammograms.

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OCCURRENCE AND CHEMISTRY OF DIHYDROXYFUMARIC ACID

Author(s):

N. Secara, Gh. Duca, L. Vlad, F. Macaev


Field: Natural product chemistry and synthesis
Type: Review
Issue: 2011 Volume 6, no.1
Pages: 29-44
Keywords: dihydroxyfumaric acid, fluorescent sensors, molecular clips, coordination polymers.
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DOI:
dx.doi.org/10.19261/cjm.2011.06(1).14

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SYNTHESIS OF NITROGEN-CONTAINING COMPOUNDS FROM HIGHER TERPENOIDS

Author(s):

Aculina Aricu


Field: Natural product chemistry and synthesis
Type: Review
Issue: 2011 Volume 6, no.1
Pages: 10-28
Keywords: synthesis, nitrogen-containing compounds, terpenoids, Beckmann rearrangement.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2011.06(1).15

Graphical Abstract:
The presence of nitrogen in the molecule is usually accompanied either by the appearance of a new activity or the intensification of original activity characteristic for the native terpenoids. This maintains alive the scientific interest in the synthesis of such compounds. The present communication put into discussion the recently elaborated  methods for preparation of the nitrogen-containing terpenic compounds.


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