The Common Acids and Bases

Two of the most important classes of chemical compounds are the acids and the bases. Acids are compounds that produce a hydrogen ion, H+, when dissolved in water. The proper way to symbolize the hydrogen ion in water is H+(aq). The (aq) stands for aqueous, meaning dissolved in water. Acids have a sour taste like that of vinegar or lemon juice. Bases are compounds that produce hydroxide ion, OH (aq), when dissolved in water. Bases have a bitter taste that you experience if you get soap in your mouth. 

Additional material dealing with acids and bases appears in Chapter 14. Only the names of the common acids and bases are considered here. 

A distinction must be made between the name of a binary acid (the solution in water) and the pure compound itself. For example, pure HC1 is a gas at room temperature and is named hydrogen chloride. But when dissolved in water, it forms the acid, HCl(aq), which ionizes to form H+(aq) and Cl (aq). 

The solution, HCl(aq), is called hydrochloric acid. Remember that the (aq) means dissolved in water. 

The binary acids are named by adding the prefix hydro- to the stem of the nonmetal followed by the -ic ending then adding the word acid. Hydrogen chloride, HC1, becomes hydro- chlor -ic acid, HCl(aq). 

---

Now, let s explore some of the common acids and bases. Acids donate protons that s their job. Stronger acids are really determined to foist their proton off onto some base. When a strong acid dissolves in water, it is essentially 100% ionized. That means essentially all of the molecular species dissociates into ions. The reaction is not an equilibrating process, so all of the starting materials are converted into products. For example, when HC1 dissolves in water, the following reaction occurs ... 

Among the first chemicals that you encounter in the laboratory are the common acids and bases. Since these materials are readily available... 

A few of the common acids and bases, together with certain salts that are discussed, are produced in such very large quantities that they are commonly referred to as the heavy chemicals (i.e., heavy in the sense of quantity production). In the discussion to follow, the methods used in the production of the more important of these chemicals are considered briefly. 

Most all reactions of this type are those between acids and bases. (See Chapter 4 for a list of the common acids and bases.) These reactions are called neutralization reactions because the acid and base neutralize the properties of the other. Water is formed in neutralization reactions. 

If you answered incorrectly, review The Common Acids and Bases, page 98. 

You will already have noticed that not every compound that contains hydrogen atoms is acidic NH3, for example, is a base. Similarly, some compounds containing the group -OH are basic, but others are acidic. An important part of understanding chemistry is being able to recognize what substances will exhibit acidic and basic properties in aqueous solution. Fortunately, most of the common acids and bases fall into a small number of fairly well-defined groups, so this is not particularly difficult. 

Reactions of this kind, involving the common acids and bases, are exceedingly fast and their rates have been measured only quite recently with the develop-... 

Learning to recognize the properties of a substance by examining a chemical formula is an important part of mastering chemistry. Fortunately, common acids and bases fall into a small number of structural categories. In this section we describe how to recognize acids and bases, hi Section 17-1 we explain how chemical structure influences acidity. 

Peruse Table 16-1 for a list of common acids and bases, noting that all the acids in the list contain a hydrogen at the beginnings of their formulas and that most of the bases contain a hydroxide. The Arrhenius definition of acids and bases is straightforward and works for many common acids and bases, but it s limited by its narrow definition of bases. 

Table 4.2 summarizes the names, formulas, and classification of some common acids and bases. 

The Arrhenius theory accounts for the properties of many common acids and bases, but it has important limitations. For one thing, the Arrhenius theory is restricted to aqueous solutions for another, it doesn t account for the basicity of substances like ammonia (NH3) that don t contain OH groups. In 1923, a more general theory of acids and bases was proposed independently by the Danish chemist Johannes Bronsted and the English chemist Thomas Lowry. According to the Bronsted-Lowry theory, an acid is any substance (molecule or ion) that can transfer a proton (H + ion) to another substance, and a base is any substance that can accept a proton. In short, acids are proton donors, bases are proton acceptors, and acid-base reactions are proton-transfer reactions ... 

Software offered with version 4.1 of ProLogP and ProLogD attempts to calculate log D values from structure. This can be very difficult for the ionizable portions of many heterocycles which are common to pharmaceutical chemistry. For the more common acids and bases encountered in environmental research, the results may be satisfactory and, at times, very helpful. Note that the sources for these programs are in van de Waterbeemd (1996). 

The words acid and base are commonly used and can be defined by their properties. The physical properties of these substances are simple. Acids taste sour (consider the taste of a lemon), and they can burn your skin. Bases taste bitter and feel slippery. Soaps and... 

A subtle, but important, point must be made before we can extend our understanding of acid-base chemistry to the reaction between a Grignard or alkyllithium reagent and a carbonyl group. The data in the table of Br /nsted acids and their conjugate bases reflect the strengths of common acids and bases when they act as Brif/nstedacids or bases. These data predict that methyllithium should react with acetylene to form methane and an acetylide ion, for example. 

So, let s proceed with a review of the basics. We ll start with another look at equilibrium, and then the structure and nomenclature of some common acids and bases. We ll next take a look at some basic pH calculations. Then, however, we ll delve into an area that you might not have seen before ionization equilibria of weak acids and bases. Finally, we ll explore the preparation and properties of buffers. 

Another structural motif, the zwitterion, is potentially present in molecules that contain both acidic and basic functional groups, a situation present in many biomolecules [81-90].However,zwitterions are intrinsically not stable (for common acids and bases) and require a large amount of stabilization by (self-) solvation and Coulomb interaction with other charges. Zwitterions and non-zwit-terions of flexible molecules sometimes assume sufficiently different geometries that the ion mobility technique can be used to distinguish between the two forms. The best examples reported to date are the sodiated oligoglycines that were found not to be zwitterions [91]. 

What interpretation can be placed on such behavior In the first place it should be noted that the reactions chosen represent true catalysis in the sense that the catalyst is not consumed in the chemical reaction. Since the behavior common to all of the catalytic species is the ability to transfer protons, it seems fair to assume that there is an interaction between the reacting molecule (or its conjugate acid or base) and the catalytic acids and bases that involves proton transfer. Finally, since the net reaction does not involve protons, we must assume a reverse transfer of protons from this last complex (substrate plus acid or base) to yield final product. 

Common acids and bases introduced in general chemistry will often be used in the same way in organic reactions. HCI and H2SO4 are strong acids, and OH is a strong base. 

A solution with a high concentration is called a stock solution. Chemists have stock solutions in the laboratory. Adding solvent, mostly water, is one of the ways of obtaining a less concentrated solution. This process is called dilution. Chemists frequently use the dilution process because many common acids and bases are purchased by chemical companies as highly concentrated stock solutions (Table 2). 

Most analytical measurements are performed on solutions (usually aqueous) of the analyte. While some samples dissolve readily in water or aqueous solutions of the common acids or bases, others require powerful reagents and rigorous treatment. For example, when sulfur or halogens are to be determined in an organic compound, the sample must be subjected to high temperatures and potent reagents to rupture the strong bonds between these elements and carbon. Similarly, drastic conditions are usually required to destroy the silicate structure of a siliceous mineral and to free the ions for analysis. 

Compare the strengths of several common acids and bases. 

Recall the lists of strong acids (Table 4-5) and strong bases (Table 4-7). These acids and bases are completely or almost completely ionized or dissociated in dilute aqueous solutions. Other common acids and bases are either insoluble or only slighdy ionized or dissociated. In addition, the solubility guidelines (page 134 and Table 4-8) allow you to determine which salts are soluble in water. Most salts that are soluble in water are also strong electrolytes. Exceptions such as lead acetate, Pb(CH3COO)2, which is soluble but does not ionize appreciably, will be noted as they are encountered. 

The common acids are other examples of inorganic compounds that are known by common rather than formal names. Some names of common acids and bases that you will use frequently in chemistry laboratory experiments are listed in Table 5.7. Although they often do not follow the rules you have been learning, they will soon become so familiar that their formulas and names will be easy to remember. 

Review the following concepts before studying this chapter. Chapter 5 names and formulas of common acids and bases Chapter 13 dissociation of ionic compounds hydrogen bonding... 

Correctly name the following common acids and bases (a) HC2H302(aq), (b) LiOHfaq),... 

As is seen from equation (1.1.16), the solvosystem concept is appropriate for describing acid-base interactions in any molecular solvent with a relatively small ionic product and, consequently, slight auto-ionization. Also, it may be used for the description of interactions in covalent melts mercury, zinc and aluminium halides should be mentioned among these. In relation to the terms acid and base , this definition is more common than those formulated by Arrhenius or BrOnstcd and Lowry, although there are charge limitations on acid and base an acid of solvent is a cation particle whereas a base one is an anion. 

Although we have analysed the sedimentary structure for the subject acids and bases much more extensively than for other common subjects (salts, organic chemistry, electrochemistry) in the chemistry curriculum, a similar sedimentary structure can be found throughout the entire curriculum with different incoherent layers being even inconsistent in several cases. 

Therefore, you must know solubility rules for solids and gases, and you must know common weak acids and bases. You should have memorized the strong acids and bases and then can assume that other acids and bases are weak. 

---