Acid-base equilibria concept

Apply acid-base equilibrium concepts to salts of strong bases and weak acids... 

Our goal in this chapter is to help you continue learning about acid-base equilibrium systems and, in particular, buffers and titrations. If you are a little unsure about equilibria and especially weak acid-base equilibria, review Chapters 14 and 15. You will also learn to apply the basic concepts of equilibria to solubility and complex ions. Two things to remember (1) The basic concepts of equilibria apply to all the various types of equilibria, and (2) Practice, Practice, Practice. 

The ability to make good estimates of acid-base equilibrium constants is an invaluable aid in thinking about organic reactions and processes. Moreover, experimental workup procedures often require pH control that can be easily understood on the basis of pKa considerations. Thus the concept of acid strength is exceedingly important and should be mastered. 

The concepts and equations of acid-base dissociation have referred chiefly to aqueous solutions. Recently, interest in the behavior of acids and bases in solvents other than water has increased considerably. The classical definition of an acid and a base, which is satisfactory for water solutions, is too limited for other solvents. Because of the great importance of the general question of the acid-base equilibrium, the clear and fruitful views of Bronsted are exhaustively considered in a special (fourth) chapter. ... 

The acidity or basicity of a solution is frequently an important factor in chemical reactions. The use of buffers of a given pH to maintain the solution pH at a desired level is very important. In addition, fundamental acid-base equihbria are important in understanding acid-base titrations and the effects of acids on chemical species and reactions, for example, the effects of complexation or precipitation. In Chapter 6, we described the fundamental concept of equilibrium constants. In this chapter, we consider in more detail various acid-base equilibrium calculations, including weak acids and bases, hydrolysis, of salts of weak acids and bases, buffers, polyprotic acids and their salts, and physiological buffers. Acid-base theories and the basic pH concept are reviewed first. 

These equilibrium constants provide a measure of thermodynamic basicity, but we also need to have some concept of kinetic basicity. For the reactions in Scheme 4.3, for example, it is important to be able to generalize about the rates of competing reactions. The most useful qualitative approach for making predictions is the hard-soft-acid-base (HSAB) concept (see Section 1.1.6), which proposes that reactions occur most readily between species that are matched in hardness and softness. Hard nucleophiles prefer hard electrophiles, whereas soft nucleophiles prefer soft electrophiles. 

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. 

In this chapter, we treat a variety of acid-base equilibrium situations to give practice in using pH calculations and concepts in a broad span of science. 

Use the concept of reversible reactions to explain acid-base equilibrium. Use Le Chatelier s principle to determine the effect on equilibrium concentrations when reaction conditions change. 

We see in Table 11-IV that the equilibrium view of acid strengths suggests that we regard water itself as a weak acid. It can release hydrogen ions and the extent to which it does so is indicated in its equilibrium constant, just as for the other acids. We shall see that this type of comparison, stimulated by our equilibrium considerations, leads us to a valuable generalization of the acid-base concept. 

First, the simple thermodynamic description of pe (or Eh) and pH are both most directly applicable to the liquid aqueous phase. Redox reactions can and do occur in the gas phase, but the rates of such processes are described by chemical kinetics and not by equilibrium concepts of thermodynamics. For example, the acid-base reaction... 

Our goal in this chapter is to help you understand the equilibrium systems involving acids and bases. If you don t recall the Arrhenius acid-base theory, refer to Chapter 4 on Aqueous Solutions. You will learn a couple of other acid-base theories, the concept of pH, and will apply those basic equilibrium techniques we covered in Chapter 14 to acid-base systems. In addition, you will need to be familiar with the log and 10 functions of your calculator. And, as usual, in order to do well you must Practice, Practice, Practice. 

In this chapter, you will continue your study of acid-base reactions. You will find out how ions in aqueous solution can act as acids or bases. Then, by applying equilibrium concepts to ions in solution, you will be able to predict the solubility of ionic compounds in water and the formation of a precipitate. 

The Catalysis Concept of Iminium Activation In 2000, the MacMillan laboratory disclosed a new strategy for asymmetric synthesis based on the capacity of chiral amines to function as enantioselective catalysts for a range of transformations that traditionally use Lewis acids. This catalytic concept was founded on the mechanistic postulate that the reversible formation of iminium ions from a,p-unsaturated aldehydes and amines [Eq. (11.10)] might emulate the equilibrium dynamics and 7i-orbital electronics that are inherent to Lewis acid catalysis [i.e., lowest unoccupied molecular orbital (LUMO)-lowering activation] [Eq. (11.9)] ... 

What is it that makes an acid an acid and a base a base We first raised those questions in Section 4.5, and we now take a closer look at some of the concepts that chemists have developed to describe the chemical behavior of acids and bases. We ll also apply the principles of chemical equilibrium discussed in Chapter 13 to determine the concentrations of the substances present in aqueous solutions of acids and bases. An enormous amount of chemistry can be understood in terms of acid-base reactions, perhaps the most important reaction type in all of chemistry. 

The appearence of a negative power of concentration, [OH-], introduces a new concept, the role of chemical equilibrium in regulating the concentrations of reactants or reaction intermediates. In this case, in Step 1 HOC1 is formed in a straightforward reversible acid-base reaction. 

The Bronsted-Lowry concept looks at the equilibrium reaction and ties the acid on the left to a base on the right, called a conjugate acid-base pair or, more simply, a conjugate pair. Suppose we were to consider an acid reacting with a compound in equilibrium with the acid s anion and the products, as... 

You can t get very far into acid-base chemistry before you run into acid-base equilibria. So, let s get started with acids and bases by first revisiting the concept of dynamic equilibria. As we said in chapter 7, a dynamic equilibrium exists in a system comprised of (at least) two states when the populations of the two states are constant, even though the members of the system are constantly changing from one state to another. We illustrated this principle with vapor pressure. Now let s consider some chemical examples. Most chemical reactions are reversible. 

Electrophilicity — (1) The property of being - electrophilic (see -> electrophile). (2) The relative reactivity of an electrophilic reagent. (It is also sometimes referred to as electrophilic power ) Qualitatively, the concept is related to Lewis acidity (- acid-base theories). However, whereas Lewis acidity is measured by relative - equilibrium constants, electrophilicity is measured by relative -> rate constants for reactions of different electrophilic... 

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