Chemical equilibrium acid-base equilibria

Acid-base equilibrium is very important to inorganic chemical reactions. Adsorption-desorption and precipitation-dissolution reactions are also of major importance in assessing the geochemical fate of deep-well-injected inorganics. Interactions between and among metals in solution and solids in the deep-well environment can be grouped into four types1 2 3 4 ... 

To probe the thermodynamics of amine encapsulation, the binding affinities for different protonated amines for 1 were investigated. By studying the stabilization of the protonated form of encapsulated amines, the feasibility of stabilizing protonated intermediates in chemical reactions could be assessed. The thermodynamic cycle for encapsulation of a hypothetical substrate (S) is shown in Scheme 7.5. The acid-base equilibrium of the substrate is defined by Ki and the binding constant of the protonated substrate in 1 is defined by K2. Previous work has shown that neutral substrates can enter 1 [94] however, the magnitude of this affinity (K4) remains unexplored. Although neutral encapsulated amines were not observable in the study of protonated substrates, the thermodynamic cycle can be completed with K3, which is essentially the acid-base equilibrium inside 1. 

Since solid acid catalysts are used extensively in chemical industry, particularly in the petroleum field, a reliable method for measuring the acidity of solids would be extremely useful. The main difficulty to start with is that the activity coefficients for solid species are unknown and thus no thermodynamic acidity function can be properly defined. On the other hand, because the solid by definition is heterogeneous, acidic and basic sites can coexist with variable strength. The surface area available for colorimetric determinations may have widely different acidic properties from the bulk material this is especially true for well-structured solids like zeolites. It is also not possible to establish a true acid-base equilibrium. 

The primary chemical interaction governing the operation of the pH optrode is the acid-base equilibrium of the indicator HA. 

FIGURE 7.4 Of the 16 chemistry topics examined (1-16) on the final exam, overall the POGIL students had more correct responses to the same topics than their L-I counterparts. Some topics did not appear on all the POGIL exams. Asterisks indicate topics that were asked every semester and compared to the L-I group. The topics included a solution problem (1), Lewis structures (2), chiral center identification (3), salt dissociation (4), neutralization (5), acid-base equilibrium (6), radioactive half-life (7), isomerism (8), ionic compounds (9), biological condensation/hydrolysis (10), intermolecular forces (11), functional group identification (12), salt formation (13), biomolecule identification (14), LeChatelier s principle (15), and physical/chemical property (16). 

In this chapter we have encountered many different situations involving aqueous solutions of acids and bases, and in the next chapter we will encounter still more. In solving for the equilibrium concentrations in these aqueous solutions, you may be tempted to create a pigeonhole for each possible situation and to memorize the procedures necessary to deal with each particular situation. This approach is just not practical and usually leads to frustration Too many pigeonholes are required, because there seems to be an infinite number of cases. But you can handle any case successfully by taking a systematic, patient, and thoughtful approach. When analyzing an acid-base equilibrium problem, do not ask yourself how a memorized solution can be used to solve the problem. Instead, ask yourself this question What are the major species in the solution, and how does each behave chemically ... 

Many real-world applications of chemistry and biochemistry involve fairly complex sets of reactions occurring in sequence and/or in parallel. Each of these individual reactions is governed by its own equilibrium constant. How do we describe the overall progress of the entire coupled set of reactions We write all the involved equilibrium expressions and treat them as a set of simultaneous algebraic equations, because the concentrations of various chemical species appear in several expressions in the set. Examination of relative values of equilibrium constants shows that some reactions dominate the overall coupled set of reactions, and this chemical insight enables mathematical simplifications in the simultaneous equations. We study coupled equilibria in considerable detail in Chapter 15 on acid-base equilibrium. Here, we provide a brief introduction to this topic in the context of an important biochemical reaction. 

The concepts of an acid, a base, and a salt are ancient ones that modern chemical science has adopted and refined. Our treatment of the subject at this stage will be mainly qualitative, emphasizing the definitions and fundamental ideas associated with acids and bases. The quantitative treatment of acid-base equilibrium systems is treated in another unit. 

The solvent can alter an acid-base equilibrium not only through the acid or basic character of the solvent itself, but also by its dielectric effect and its capacity to solvate the different species which participate in the process. Whilst the acid or basic force of a substance in the gas phase is an intrinsic characteristic of the substance, in solution this force is also a reflection of the acid or basic character of the solvent and of the actual process of solvat-ation. For this reason the scales of acidity or basicity in solution are clearly different from those corresponding to the gas phase. Thus, toluene is more acid than water in the gas phase but less acid in solution. These differences between the scales of intrinsic acidity-basicity and in solution have an evident repercussion on the order of acidity of some series of chemical substances. Thus, the order of acidity of the aliphatic alcohols becomes inverted on passing from the gas phase to solution ... 

Water reacts with HCl, and the organic acid known as formic acid (HCOOH, 1) also reacts with water as a weak acid, as shown. Formic acid is a much weaker acid than HCl. When 1 reacts with water, the conjugate base is the formate anion, 2, and the conjugate acid is the hydronium ion. If 1 is a weaker acid than HCl, the equilibrium for 1 + HgO lies to the left in the reaction shown when compared to the reaction of HCl + H2O in Section 2.1. Note the (aq) term indicates solvation by the solvent water. Note also that the term reaction is used for the acid-base equilibrium. The acid-base equilibria shown for HCl and HCOOH are chemical reactions that generate two products the formate anion (HCOO , 2) and the hydronium ion (from 1) or the hydronium ion and the chloride ion (from HCl). 

Keywords Activated carbon Chemical treatment Adsorption Scanning electron microscopy Small-angle X-ray scattering Quasi-equilibrium acid-base titration... 

Brain tissue had a special chemical composition. In the adult it contained more lipids than proteins and little glycogen. Little was known about the proteins, except for the recent findings of an active metabolism of nucleoproteins, presumably the underlying mechanism of chromatolysis. Lipids belonged to the structural, not the metabolic reserve pool, and an adult animal starved to death showed the same amount of brain lipids as its litter mate that had been fed properly. Much work had been done for several generations on the chemistry of brain lipids since they were often quite difierent from those found in other tissues. Their function was a puzzle they obviously acted as insulators in myelin and they provided anionic charges to the acid-base equilibrium of the tissue. Beyond that, they could only be supposed to play an active if as yet undefined role in the functioning of nervous membranes. 

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