|
Specific Ion Interaction Theory
In theoretical chemistry, Specific ion Interaction Theory (SIT theory) is a theory used to estimate single- ion activity coefficients in electrolyte solutions at relatively high concentrations. It does so by taking into consideration ''interaction coefficients'' between the various ions present in solution. Interaction coefficients are determined from equilibrium constant values obtained with solutions at various ionic strengths. The determination of SIT interaction coefficients also yields the value of the equilibrium constant at infinite dilution. Background The need for this theory arises from the need to derive activity coefficients of solutes when their concentrations are too high to be predicted accurately by Debye-Hückel theory. These activity coefficients are needed because an equilibrium constant is defined in thermodynamics as a quotient of activities but is usually measured using concentrations. The protonation of a monobasic acid will be used to simplify the e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Theoretical Chemistry
Theoretical chemistry is the branch of chemistry which develops theoretical generalizations that are part of the theoretical arsenal of modern chemistry: for example, the concepts of chemical bonding, chemical reaction, valence, the surface of potential energy, molecular orbitals, orbital interactions, and molecule activation. Overview Theoretical chemistry unites principles and concepts common to all branches of chemistry. Within the framework of theoretical chemistry, there is a systematization of chemical laws, principles and rules, their refinement and detailing, the construction of a hierarchy. The central place in theoretical chemistry is occupied by the doctrine of the interconnection of the structure and properties of molecular systems. It uses mathematical and physical methods to explain the structures and dynamics of chemical systems and to correlate, understand, and predict their thermodynamic and kinetic properties. In the most general sense, it is explanation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acid Dissociation Constant
In chemistry, an acid dissociation constant (also known as acidity constant, or acid-ionization constant; denoted ) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction :HA A^- + H^+ known as dissociation in the context of acid–base reactions. The chemical species HA is an acid that dissociates into , the conjugate base of the acid and a hydrogen ion, . The system is said to be in equilibrium when the concentrations of its components will not change over time, because both forward and backward reactions are occurring at the same rate. The dissociation constant is defined by :K_\text = \mathrm, or :\mathrmK_\ce = - \log_ K_\text = \log_\frac where quantities in square brackets represent the concentrations of the species at equilibrium. Theoretical background The acid dissociation constant for an acid is a direct consequence of the underlying thermodynamics of the dissociation reaction; the p'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bromley Equation
The Bromley equation was developed in 1973 by Leroy A. Bromley with the objective of calculating activity coefficients for aqueous electrolyte solutions whose concentrations are above the range of validity of the Debye–Hückel equation. This equation, together with Specific ion interaction theory (SIT) and Pitzer equationsChapter 3. Pitzer, K.S. ''Ion interaction approach: theory and data correlation'', pp75-153. is important for the understanding of the behaviour of ions dissolved in natural waters such as rivers, lakes and sea-water. Description Guggenheim had proposed an extension of the Debye-Hückel equation which is the basis of SIT theory. The equation can be written, in its simplest form for a 1:1 electrolyte, MX, as :\log \gamma_ = \frac+\beta b. \gamma_ is the mean molal activity coefficient. The first term on the right-hand side is the Debye–Hückel term, with a constant, ''A'', and the ionic strength ''I''. β is an interaction coefficient and ''b'' the molality ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sechenov
Doctor Ivan Mikhaylovich Sechenov (russian: Ива́н Миха́йлович Се́ченов; , Tyoply Stan (now Sechenovo) near Simbirsk, Russia – , Moscow), was a Russian psychologist, physiologist, and medical scientist. The very famous Russian scientist of human reflexes Pavlov referred to him as the "Father of Russian physiology and scientific psychology" at his time, but today we rather consider Sechenov as scientist in medical physiology, and father of Russian physiology and also researcher in psychology, but also in relation to it in neurological physiology. Sechenov is also considered one of the originators of objective psychology as an attempt to introduce objectiveness in the rather wide Russian psychology field and the many developments in it. Biography Sechenov was born in the village of Tepli Stan, which is now known as Sechenov, Gorky Oblast. He was a son of a nobleman and a peasant. Sechenov was first taught by private tutors and he had mastered German ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molar Concentration
Molar concentration (also called molarity, amount concentration or substance concentration) is a measure of the concentration of a chemical species, in particular of a solute in a solution, in terms of amount of substance per unit volume of solution. In chemistry, the most commonly used unit for molarity is the number of moles per liter, having the unit symbol mol/L or mol/ dm3 in SI unit. A solution with a concentration of 1 mol/L is said to be 1 molar, commonly designated as 1 M. Definition Molar concentration or molarity is most commonly expressed in units of moles of solute per litre of solution. For use in broader applications, it is defined as amount of substance of solute per unit volume of solution, or per unit volume available to the species, represented by lowercase c: :c = \frac = \frac = \frac. Here, n is the amount of the solute in moles, N is the number of constituent particles present in volume V (in litres) of the solution, and N_\text is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molal
Molality is a measure of the number of moles of solute in a solution corresponding to 1 kg or 1000 g of solvent. This contrasts with the definition of molarity which is based on a specified volume of solution. A commonly used unit for molality in chemistry is mol/ kg. A solution of concentration 1 mol/kg is also sometimes denoted as ''1 molal''. The unit ''mol/kg'' requires that molar mass be expressed in ''kg/mol'', instead of the usual ''g/mol'' or ''kg/kmol''. Definition The molality (''b''), of a solution is defined as the amount of substance (in moles) of solute, ''n''solute, divided by the mass (in kg) of the solvent, ''m''solvent: :b = \frac In the case of solutions with more than one solvent, molality can be defined for the mixed solvent considered as a pure pseudo-solvent. Instead of mole solute per kilogram solvent as in the binary case, units are defined as mole solute per kilogram mixed solvent. Origin The term ''molality'' is formed in analogy to ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glass Electrode
A glass electrode is a type of ion-selective electrode made of a doped glass membrane that is sensitive to a specific ion. The most common application of ion-selective glass electrodes is for the measurement of pH. The pH electrode is an example of a glass electrode that is sensitive to hydrogen ions. Glass electrodes play an important part in the instrumentation for chemical analysis and physicochemical studies. The voltage of the glass electrode, relative to some reference value, is sensitive to changes in the activity of a certain type of ions. History The first studies of glass electrodes (GE) found different sensitivities of different glasses to change the medium's acidity (pH), due to the effects of the alkali metal ions. In 1906, M. Cremer, the father of Erika Cremer, determined that the electric potential that arises between parts of the fluid, located on opposite sides of the glass membrane is proportional to the concentration of acid (hydrogen ion concentratio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pitzer Equations
Pitzer equations are important for the understanding of the behaviour of ions dissolved in natural waters such as rivers, lakes and sea-water. They were first described by physical chemist Kenneth Pitzer. The parameters of the Pitzer equations are linear combinations of parameters, of a virial expansion of the excess Gibbs free energy, which characterise interactions amongst ions and solvent. The derivation is thermodynamically rigorous at a given level of expansion. The parameters may be derived from various experimental data such as the osmotic coefficient, mixed ion activity coefficients, and salt solubility. They can be used to calculate mixed ion activity coefficients and water activities in solutions of high ionic strength for which the Debye–Hückel theory is no longer adequate. They are more rigorous than the equations of specific ion interaction theory (SIT theory), but Pitzer parameters are more difficult to determine experimentally than SIT parameters. Historica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Debye–Hückel Equation
The chemists Peter Debye and Erich Hückel noticed that solutions that contain ionic solutes do not behave ideally even at very low concentrations. So, while the concentration of the solutes is fundamental to the calculation of the dynamics of a solution, they theorized that an extra factor that they termed gamma is necessary to the calculation of the activity coefficients of the solution. Hence they developed the Debye–Hückel equation and Debye–Hückel limiting law. The activity is only proportional to the concentration and is altered by a factor known as the activity coefficient \gamma. This factor takes into account the interaction energy of ions in solution. Debye–Hückel limiting law In order to calculate the activity a_C of an ion C in a solution, one must know the concentration and the activity coefficient: a_C = \gamma \frac\mathrm\mathrm, where * \gamma is the activity coefficient of C, * \mathrm is the concentration of the chosen ''standard state'', e.g. 1 m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Determination Of Equilibrium Constants
Equilibrium constants are determined in order to quantify chemical equilibria. When an equilibrium constant is expressed as a concentration quotient, :K=\frac it is implied that the activity quotient is constant. For this assumption to be valid, equilibrium constants must be determined in a medium of relatively high ionic strength. Where this is not possible, consideration should be given to possible activity variation. The equilibrium expression above is a function of the concentrations etc. of the chemical species in equilibrium. The equilibrium constant value can be determined if any one of these concentrations can be measured. The general procedure is that the concentration in question is measured for a series of solutions with known analytical concentrations of the reactants. Typically, a titration is performed with one or more reactants in the titration vessel and one or more reactants in the burette. Knowing the analytical concentrations of reactants initially in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Conjugate Base
A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid donates a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as in the reverse reaction it loses a hydrogen ion. On the other hand, a conjugate base is what is left over after an acid has donated a proton during a chemical reaction. Hence, a conjugate base is a species formed by the removal of a proton from an acid, as in the reverse reaction it is able to gain a hydrogen ion. Because some acids are capable of releasing multiple protons, the conjugate base of an acid may itself be acidic. In summary, this can be represented as the following chemical reaction: :acid + base conjugate\ base + conjugate\ acid Johannes Nicolaus Brønsted and Martin Lowry introduced the Brønsted–Lowry theory, which proposed that any compound that can transfer a proton to any other compound is an acid, and the compound that accepts the proton is a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
