Abstract
Until recently, due to the absence of other suitable approaches, equilibrium concentrations in acid-base systems have been studied exclusively by measuring the pH of a solution. However, this method can not be used for organic (non-aqueous) solvent solutions. It is known that the ionic strength of a solution, which is a fundamental component in assessing the activity coefficient and the thermodynamic dissociation constant of an electrolyte, is influenced by the ions present in the system. The concentration of these ions is variable during interactions in aqueous and more complex non-aqueous solutions, which differ significantly in their physicochemical properties (boiling temperature, structure, permittivity, autoprotolysis constant, solvating ability, dipole moment, viscosity, etc.). Meanwhile, in order to obtain more objective and valid estimates of acid-base interactions, in addition to the activity of hydrogen ions, appropriate account should be taken of the equilibrium concentrations of all particles in the solution, which affect its ionic strength. In this article, on the basis of the law of mass action and equations describing equilibrium processes, the ionic product of a solvent, electrical neutrality and material balance in a solution, the corresponding equations were derived and a method was proposed for considering the effect of the concentrations of all particles in the system (not only hydrogen ions – pH), significantly affecting the properties of acid-base equilibrium systems. The proposed method can also be used to obtain the dependence of the equilibrium concentrations of all process substances on the state of the medium (test solution), determined by various chemical and instrumental methods in logarithmic coordinates, which makes it pos-sible to directly assess the equilibrium concentra- tions of all particles present in the system.
Highlights
Until recently, due to the absence of other suitable approaches, equilibrium concentrations in acidbase systems have been studied exclusively by measuring the pH of a solution
The basis of the law of mass action and equations describing equilibrium processes, the ionic product of a solvent, electrical neutrality and material balance in a solution, the corresponding equations were derived and a method was proposed for considering the effect of the concentrations of all particles in the system, significantly affecting the properties of acid-base equilibrium systems
The proposed method can be used to obtain the dependence of the equilibrium concentrations of all process substances on the state of the medium, determined by various chemical and instrumental methods in logarithmic coordinates, which makes it pos-sible to directly assess the equilibrium concentrations of all particles present in the system
Summary
25,0 0,2 oС на рН-метре-милливольтметре Metrohm-632 (Швейцария). Водородная (вернее, лиониевая) функция стеклянного электрода проверена в широком диапазоне ра(ROH+) методом, основанном на измерении рН (или Е, В в зависимости от природы растворителя) в ряде буферных растворов от сильнокислой до сильноосновной среды с сохранением градиента с угловым коэффициентом 59мВ/lgа(Н+) при 25 oС. 1. Кривая титрования 20 мл смеси кислот HCl + ClCH2COOH раствором гидроксида тетрабутиламмония в среде ацетона. 1 интегральная кривая титрования смеси двух кислот [6,7,8] преобразована в логарифмическую диаграмму, которая дает возможность оценить равновесные концентрации частиц [HCl], [Cl-], [ClCH2COOH], [ClCH2COO-] (уравнения (3)–(6)) во всем диапазоне изменения ра(Н2М+) – иона лиония. По данным титрования оценены равновесные концентрации, ионная сила, коэффициенты активности всех участников кислотно-основной системы и показатели термодинамических констант диссоциации хлороводородной и хлоруксусной кислот. Приведены примеры экспресс-определения равновесных концентраций всех частиц в растворе a(H2M+), [HCl], [Cl-], [ClCH2COOH] и [ClCH2COO-], термодинамических констант диссоциации обеих кислот, позволяющих проследить за динамикой изменения соотношений равновесных частиц на всем протяжении кривой титрования смеси сильных и слабых электролитов Приведенная концепция вполне применима для исследования кислотно-основных взаимодействий смесей сильных и слабых электролитов
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