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https://doi.org/10.29013/AJT-19-11.12-48-51
Yakhshieva Zuhra Ziyatovna, doctor of philosophy in chemistry, Professor of Jizzakh State Pedagogical Institute E-mail: yaxshiyeva67@mail.ru Bakahonov Anvar Akobirobvich, Lecturer of Department of Chemistry Teaching Methodology,
Jizzakh State Pedagogical Institute Kurbonova Dilafruz Sobirovna, holder of master's degree, Jizzakh State Pedagogical Institute
OPTIMIZATION OF AMPEROMETRIC CONDITIONS FOR THE DETERMINATION OF MOLYBDENUM IONS IN ANTHROPOGENIC OBJECTS
Abstract. The current-voltage behavior in the selected medium on the corresponding electrode of both titratable molybdenum ions and an organic reagent, as well as all other components of the analyzed solution involved in the titration during optimization of amperometric titration conditions, is investigated. We studied the electrochemical behavior of N-methylanabazine - a-azo-^-naphthol, on a platinum disk microanode; oxidation curves taken at different temperatures of the test solution and the number of revolutions of the platinum disk microanode in all studied buffer mixtures and background electrolytes; the diffusion nature of the limiting current of the electrooxidation of the reagents and the cathodic reduction of titrated metal ions is established, and their irreversible nature is established by the method of logarithmic analysis. On their basis, methods have been developed for the amperometric titration of molybdenum ions with one or two indicator electrodes in aqueous, non-aqueous, mixed media.
Keywords: amperometry, amperometric titration, organic reagents, expressivity, titration, selectivity, selectivity, correctness, reproducibility, electrical conductivity.
Relevance. The growing demand for molybde- The importance of molybdenum in science, num and its alloys is linked with the development technology, industry and the national economy of such industries as instrument manufacturing, is enormous, as it possesses unique properties and electronics, nuclear and electric power industry - original characteristics. This in turn requires the determinants of the technological progress of the improvement of existing methods for determining whole world, which makes the problem of analysis molybdenum, the development of new methods of environmental objects with micro-content of this with the aim of establishing their macro-, mimetal relevant. Accuracy, correctness and reproduc- cro- and trace concentrations in anthropogenic ibility, along with the rapidity of determination, are objects, since their micro-quantities play an im-especially important because of the high demand of portant and decisive role in solving various ana-the determined molybdenum for both its biological lytical, electrochemical, medical, environmental and physiological properties. and other tasks.
Based on the third direction of the Strategy for the Further Development of the Republic of Uzbekistan, aimed at "rising industry to a new level, further intensifying the production of finished products based on deep processing of local raw materials, mastering the production of fundamentally new types of products and technologies", the main tasks are determined. The regulatory measures taken in this direction have achieved certain results, especially, high-level scientific research has been organized and large-scale measures have been taken to ensure the import and substitution of chemical reagents for the local market. The amperometric method of analysis is based on establishing the end point of titration by the diffusion anode or cathode current, while measuring the current passing through the cell at a certain potential difference (AE) on the electrode. This current is considered as a function of a useful analytical signal from the volume (concentration) of the titration solution - N-methylanabazine - a-azo-^-naphthol. An indicator electrode for amperometric titration of metals is a rotating solid platinum electrode. Such titration is based on the same laws as in quantitative polarography and voltammetry, where a direct proportional (linear) relationship between the diffusion current and the concentration of the analyzed substance is observed.
After conducting preliminary experiments for optimization of molybdenum ions titration conditions, the influence of the external voltage, the nature and concentration of the background electrolyte and the buffer mixture, as well as foreign cations interfering with anions and complex compounds, were studied.
The experiment were conducted under the following conditions: electrode voltage: 0.75 V test solution volume - 10 ml, temperature - RT(20-25 °C), titrant concentration 0.01 M.
To increase the electrical conductivity of the ti-tratable medium and improve the shape of the curves for the determination of molybdenum (VI) with a solution of N-methylanabazine - a-azo-^-naphthol,
we studied the effect of various concentrations of buffer mixtures and background electrolytes, which significantly increase the accuracy of the data and the reproducibility of the developed methods. The effect of various background electrolytes and buffer mixtures in the range of pH 1.60-12.50 was investigated.
The electrochemical determination of molybdenum (VI) with a solution of N-methylanabazine
- a-azo-^-naphthol was studied on the background of hydrochloric, nitric, perchloric, sulfuric acids, in a Britton-Robinson buffer and solutions of alkali metal chlorides. It was shown that molybdenum (VI) is well titrated in all studied background electrolytes, forming strong complex compounds with N-methylanabazine
- a-azo-^-naphthol, therefore, its electrochemical behavior was studied on the background of hydrogen chloride, perchloric and sulfuric acids, sodium chlorides and potassium, a Britton-Robinson buffer in a pH range of 1.62-12.5. The maximum sensitivity, correctness and reproducibility of the determination of molybdenum (VI) with a solution of N-methylanabazine
- a-azo-^-naphthol are observed in strongly acidic media, and experiments have shown that amperometric determination of molybdenum (VI) is possible even in the presence of concomitant cations, and the best background the electrolyte is 1.0 M potassium chloride, because only on it the best results were obtained.
To improve the shape of the curves and increase the electrical conductivity of the titrated medium, as well as to suppress migration currents when determining molybdenum (VI) with a solution of N-methylanabazine - a-azo-^-naphthol, the effect of the universal Britton-Robinson buffer in the pH range of 1.81-12 was also studied.
A series of experiments aimed at clarifying the nature of the influence of this factor on the conditions of amperometric titration of molybdenum (VI) with a solution of N-methylanabazine - a-azo-^-naphthol was carried out at their concentrations equal to 0.2 M in the volume of titrated solution equal to 10.0 ml, at the temperature of the test solution 20 ± 6 °C.
The calculation of the found amount of metal (component) in the titrated sample was carried out according to the formula known used in literature:
P = Vtaa x m x N x 1000 mg; where: Vtaa- is the volume of reagent used for titration (ml);
m - is the coefficient of the piston microburette (0.0029 ml);
N - is the equivalent mass of the titrated metal.
It was experimentally established that the best results when titrating molybdenum with a solution of N-methylanabazine are observed in acidic media at pH 1.81-2.82, resulting in the formation of strong complex compounds.
Since the voltage value should have a significant effect on the type of curves, conditions and results of metal determination, we studied the effect of the voltage value on titration of molybdenum (VI) with a solution of N-methylanabazine - a-azo-^-naphthol under the following optimal conditions: background - universal buffer with a pH of 1.81-2.62, the concentration of titrant is 0.001 M, the volume of the titrated solution is 8-10.0 ml, the temperature is about 24 °C. The voltage on the platinum indicator electrodes was changed in the range of 0.20-1.25 V in steps of 0.25 V.
The results of the experiment show that the average value of the titrant consumption at the titration endpoint depends on the voltage supplied to the indicator electrodes, where the average titrant consumption at the titration endpoint depends on the potential difference (AE) supplied to the platinum indicator electrodes.
Determination of molybdenum (VI) with a solution of N-methylanabazine - a-azo-^-naphthol in various real industrial materials and natural objects is a necessary and urgent task of modern electro-analytical chemistry. Therefore, the possibility and
optimized conditions of amperometric titration of molybdenum (VI) with a solution of N-methylanabazine - a-azo-^-naphthol in a wide range of their concentrations have been shown and optimized, and with appropriate selection of the determination conditions, it becomes sensitive and highly selective.
For a successful study, the influence of the potential supplied to the indicator electrodes (0.25-1.25 V) on the shape of the curves, conditions and results of amperometric titration of molybdenum (VI) with a solution of N-methylanabazine - a-azo-^-naphthol was studied. As a rule, the concentration of the titrating reagent should be several orders of magnitude higher than the content of the metals being determined. The titrant is added in small portions of a precision piston microburette, due to which dilution of the test solution can be neglected.
It was found that the curves that are optimal in shape and the best titration results are observed at a potential difference (AE) on a platinum indicator electrode equal to 0.75 V.
The experimental results obtained indicate that the developed amperometric methods for the determination of molybdenum (VI) ions with a solution of N-methylanabazine - a-azo-^-naphthol are distinguished by high metrological characteristics and analytical parameters that allow them to be recommended in the analysis of real materials, ores, alloys, minerals, tails and other objects.
Summing up the results of the studies, it is necessary to note that the obtained experimental data served as the basis for the development of amperometric methods for the determination of ions of the studied noble metals in their model binary, ternary and more complex mixtures that simulate natural objects and industrial materials, thereby showing the possibility of their real practical application in the analysis of objects environment and industrial materials.
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