VIRTUAL LABORATORY PRACTICAL WORK AS A WAY OF STUDYING NATURAL DISCIPLINES

In the article the way of using information technology in the natural education is activated, such as computer modeling of chemical, physical or biological phenomenon processes, introduction into the educational process of the virtual laboratory works. The relevance of the introduction of virtual laboratories in educational practice is due, firstly, to the information challenges of the time, and secondly, the regulatory requirements for the organization of the educational process of general secondary and higher education. It is mentioned that the use of virtual laboratories in the educational process allows students to conduct experiments with equipment and materials that he is able to use due to lack of a real laboratory or its lack of technical content, get practical skills of conducting experiments of integrated natural direction initiating computer models and the process of operation of unique equipment of chemical, physical, biological laboratory, to study dangerous in the real situation processes and phenomena of natural origin, without fear of possible consequences. The article reveals the advantages and disadvantages of using a virtual laboratory workshop during the study of natural sciences. Possibilities of modern virtual laboratories of a natural direction which allow to model objects and processes of the surrounding world and also to organize computer access to the real laboratory equipment. The possibility of realization of a virtual laboratory workshop on chemical disciplines of the natural cycle in the environment of a virtual simulator of the laboratory IrYdiumChemistryLab is shown. This virtual laboratory involves the formulation of specific tasks or the formation of its own strategy for planning the experiment,the resource immediately differs in the ability to intervene in the program and design your own virtual experiment Created on the basis of IrYdiumChemistryLab virtual laboratory works allow to prepare diluent of various concentrations, to calculate and measure concentrations of ions in solutions of strong and weak electrolytes, to titrate, etc. Virtual laboratories must be present in the practice of teaching natural sciences (chemistry, physics, biology). The need to use a virtual laboratory workshop during distance learning is especially relevant.

Predictive models for the phase behaviour and solution properties of weak electrolytes: nitric, sulphuric, and carbonic acids

The distribution of ionic species in electrolyte systems is important in many fields of science and engineering, ranging from the study of degradation mechanisms to the design of systems for electrochemical energy storage. Often, other phenomena closely related to ionic speciation, such as ion pairing, clustering and hydrogen bonding, which are difficult to investigate experimentally, are also of interest. Here, we develop an accurate molecular approach, accounting for reactions as well as association and ion pairing, to deliver a predictive framework that helps validate experiment and guides future modelling of speciation phenomena of weak electrolytes. We extend the SAFT-VRE Mie equation of state [D. K. Eriksen et al., Mol. Phys., 2016, 114, 2724–2749] to study aqueous solutions of nitric, sulphuric, and carbonic acids, considering complete and partially dissociated models. In order to incorporate the dissociation equilibria, correlations to experimental data for the relevant thermodynamic equilibrium constants of the dissociation reactions are taken from the literature and are imposed as a boundary condition in the calculations. The models for water, the hydronium ion, and carbon dioxide are treated as transferable and are taken from our previous work. We present new molecular models for nitric acid, and the nitrate, bisulfate, sulfate, and bicarbonate anions. The resulting framework is used to predict a range of phase behaviour and solution properties of the aqueous acids over wide ranges of concentration and temperature, including the degree of dissociation, as well as the activity coefficients of the ionic species, and the activity of water and osmotic coefficient, density, and vapour pressure of the solutions. The SAFT-VRE Mie models obtained in this manner provide a means of elucidating the mechanisms of association and ion pairing in the systems studied, complementing the experimental observations reported in the literature.

Fast and Slow EQCM Response of Zwitterionic Weak Electrolytes to Changes in the Electrode Potential: A pH-Mediated Mechanism

Using a fast electrochemical quartz crystal microbalance (EQCM), zwitterionic electrolytes were studied with regard to changes of resonance frequency and resonance bandwidth after the electrode potential was switched. In addition...

Applied aspects of acid-base interactions and modelling equilibrium concentrations in two-component acid mixtures

Fundamental and applied research into aqueous and non-aqueous solutions of strong and weak electrolytes remains to be highly relevant, which fact is confirmed by a large number of Russian and foreign publications. In almost all such publications, acid-base interactions are considered exclusively with regard to changes in hydrogen ion concentrations. However, the ionic strength of solutions is determined by all ions present in the system, the concentration of which varies during interactions. This is particularly true for potentiometric titration of strong and weak electrolytes not only in aqueous, but also in more complex non-aqueous solutions, which differ significantly in their basic properties (dielectric constant, ionic product, dipole moment, viscosity, etc.). In the study of equilibria, it is more feasible to develop model representations that would greatly simplify and facilitate the computation and evaluation of certain properties of the system under consideration. In this work, acid-base interactions are presented in the form of equations based on mass action laws and those describing equilibrium processes, solvent ionic product, electroneutrality and material balance in electrolyte systems. The proposed equations consider the effect of the concentrations of all charged particles in the system (not only of hydrogen ions – pH) on the ionic strength of the solution, activity coefficients and, as a consequence, the thermodynamic dissociation constant. In addition, these equations allow the dependence between the equilibrium concentrations of all charged particles and the solution acidity determined by the potentiometric method to be expressed in convenient and objective logarithmic coordinates, thus facilitating estimation of the concentration of all particles at any moment of titration.

CONSTANTS OF ELECTROLYTIC DISSOCIATION OF THE LITHIUM, SODIUM AND POTASSIUM SULFATES IN AQUEOUS ISOPROPANOL SOLUTIONS

At introduction of isopropyl alcohol in saturated aqueous solutions of sulfates of lithium, sodium and potassium at 25 °C physico-chemical properties of the studied systems Li2SO4-H2O-C3H7OH, Na2SO4-H2O-C3H7OH and K2SO4-H2O-C3H7OH are changed. This reduces the density of solutions and salt content in aqueous isopropanol solutions due to a decrease in solubility of salts. It is shown that the variation of the volume content of alcohol from 0% to 90% results in the decrease of Li2SO4 solubility 1280 times, Na2SO4 – 548 times, K2SO4 – in 278 times. Alcohol additives also affect the degree of electrolytic dissociation of salt in aqueous isopropanol solutions. To study the electrochemical properties of salts we used conductometric method based on the measurement of the molar conductivity of solutions depending on salt concentration. In aqueous solutions, alkali metal sulfates exhibit the properties of strong electrolytes and almost completely dissociate into ions. When the volume content of isopropanol in the solution is more than 30%, alkali metal sulfates begin to show the properties of weak electrolytes, as evidenced by the correlation of the molar conductivity of the diluted solution with the salt concentration under the equation describing the state of weak electrolytes. From the transformations of experimental data in the coordinates of this equation, the values of the electrolytic dissociation constants of the studied salts were determined, which vary (8.30 ± 0.01)·10-5 to (4,35 ± 0,01)·10-8 (mol/l)2 when varying the alcohol content from 30 to 90% volume. It is shown that isopropanol additives reduce the constant (and hence the degree) of electrolytic dissociation of alkali metal sulfates: the higher the alcohol concentration in the solution, the weaker the salt becomes as an electrolyte. The value of the electrolytic dissociation constant depends on the nature of the salt: with an increase in the size of the sulfate cation, the electrolytic dissociation constant decreases.

Investigation of temperature effect on the electrical conductivity of alcohol solutionssodium and potassium alcoholates

Earlier, we studied the electrical conductivity of inorganic salts in a number of alcohols (ethanol, propanol-2, and butanol-1) at room temperature and found that alcoholic solutions of inorganic salts are weak electrolytes. It is known that an increase in the temperature of salt solutions leads to an increase in electrical conductivity due to an increase in the mobility of their ions in the solvent medium. To study the temperature dependence of the electrical conductivity of aqueous solutions of electrolytes, we proposed an approach based on the study of the effect of temperature on the equivalent electrical conductivity of solutions at infinite dilution λ∞. Using this approach, we studied the electrical conductivity of aqueous solutions of a number inorganic salts (nitrates, acetates, and phosphates), carboxylic acids, and amino acids as a function of temperature. It was found that for these solutions the dependence λ∞(Т) is described by the exponential Arrhenius equation λ∞ = Аexp(-E/(RT)). This equation was used to describe the temperature dependence of the ultimate equivalent conductivity for solutions of a number of inorganic salts (calcium and nitrate calcium, cadmium, lithium and potassium iodides, chloride, iodide and ammonium nitrate, silver nitrate and sodium bromide) in ethanol. This article investigated and demonstrated the possibility of describing the experimental data λ∞(Т) for solutions of ethylates, propylates and isopropylates of sodium and potassium in the corresponding alcohols (ethylates in ethanol, propylates in propanol, isopropylates in isopropyl alcohol) using the same equation.

Investigation of temperature effect on the electrical conductivity of solutions inorganic salts in ethanol

The electrical conductivity of the solutions depends on the nature of the solute and solvent. For a solvent, the main parameter is the dielectric constant. Since the dielectric constant of alcohols is much less than the dielectric constant of water, the electrical conductivity of alcoholic solutions of salts is less than the electrical conductivity of their aqueous solutions. Therefore, alcoholic solutions of inorganic salts are weak electrolytes. We previously studied the electrical conductivity of inorganic salts in a number of alcohols (ethanol, propanol-2 and butanol-1) at room temperature. It is of interest to study the effect of temperature on the electrical conductivity of salts in alcohols. Obviously, an increase of temperature salt solutions leads to an increase in their electrical conductivity. To study the temperature dependence of the electrical conductivity of aqueous solutions electrolytes, we proposed an approach based on the study of the effect of temperature on the equivalent electrical conductivity of solutions at infinite dilution λ∞. Using this approach, we studied the electrical conductivity of aqueous solutions of a number of inorganic salts, carboxylic acids, and amino acids as a function of temperature. It has been established that for these solutions the dependence λ∞(Т) is described by the exponential Arrhenius equation λ∞ = Аexp(-E/(RT)). However, such studies have not been conducted for alcoholic salt solutions. In this regard, this article explores the possibility of describing the experimental data λ∞(Т) for solutions of certain inorganic salts in ethanol by this equation. It is shown that the Arrhenius equation with the found activation energies adequately describes the temperature dependence of the ultimate equivalent conductivity for solutions of a number of inorganic salts (chloride and calcium nitrate, cadmium iodide, lithium and potassium chloride, chloride, iodide and ammonium nitrate, silver nitrate and sodium bromide) in ethyl alcohol.

Predictive models for the phase behaviour and solution properties of weak electrolytes: nitric, sulphuric, and carbonic acids

SAFT-VRE Mie allows for elucidating association and ion pairing in weak electrolyte systems.