Reactions of Acids and Bases

Typical reactions of acids and bases include the reactions of adds with metals, bases, and carbonate or bicarbonate ions. For example, when you drop an antacid tablet in water, the bicarbonate ion and citric acid in the tablet react to produce carbon dioxide bubbles, water, and a salt. A salt is an ionic compound that does not have as the cation or OH as the anion. 

Write balanced equations for reactions of acids with metals, carbonates, and bases. 

Acids react with certain metals to produce hydrogen gas (H2) and a salt. Active metals include potassium, sodium, calcium, magnesium, aluminum, zinc, iron, and tin. In these single replacement reactions, the metal ion replaces the hydrogen in the acid. 

When the metal Al(5) reacts with HCl, it forms H2 (g) and Al +, which is balanced by 3CF from HCl to give the salt AIQ3 (ag). Using the formula of the salt gives the unbalanced eqnation. 

Now the equation can be balanced with the proper coefficients. 2Al(j) + 6HCl(a ) ------------ 3H2(g) + 2AlCl3(a ) 

Write the reactants and products. When a metal reacts with an acid, the products 

EXAMPLE 14.1 Identifying Brensted-Lowry Acids and Bases and Their Conjugates 

In each reaction, identify the Bronsted-Lowry acid, the Bronsted-Lowry base, the conjugate acid, and the conjugate base. 

The reaction between HCI and KOH is aiso a doubie-dispiacement reaction (see Section 7.10). 

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A. HuLANlCKl, Reactions of Acids and Bases in Analytical Chemistry, Ellis Horwood (Wiley), Chichester, 1987, 308 pp. 

Although this section provides only a brief introduction to equilibrium, the principles presented here arc critically important, because the tendency of reactions to proceed toward equilibrium is the basis of much of chemistry. The material in this section lays the foundation for the next five chapters, including phase changes, the reactions of acids and bases, and redox reactions. 

Acids and bases are extremely common, as are the reactions between acids and bases. The driving force is often the hydronium ion reacting with the hydroxide ion to form water. The chapter on Equilibrium describes the equilibrium reactions of acids and bases, as well as some information concerning acid—base titration. After you finish this section, you may want to review the acid-base part of the Equilibrium chapter. 

There is another common way to classify chemical reactions acid-base reactions, oxidation-reduction reactions, and reactions of more complicated types (beyond the scope of this book). Acid-base reactions are considered to involve the reactions of hydrogen ions with hydroxide ions. The reactions of acids and bases will be taken up in this section, and a more sophisticated view of these reactions is presented in Chapter 19. Oxidation-reduction reactions involve the transfer of electrons from one substance to another. Many combination reactions, many decomposition reactions, all single substitution reactions, and all combustion reactions are of this type, but more complex examples are presented in Chapters 16 and 17. 

The reactions of acids with active metals fit into the single substitution class discussed in Section 8.3. Reactions of acids with bases are double substitution reactions, also discussed in Section 8.3. However, the reactions of acids and bases are so important that they have a special terminology that we need to know. 

The most important reactions of acids and bases are their reactions with each other to form salts and water ... 

Under I, Lewis and Seaborg (47) have considered the kinetics of the reaction of acids and bases, using the fading of trinitrophenylmethide ion in acid solution as an example, but another kinetic interpretation has been offered by Kilpatrick (48), who considers the reaction to be an... 

Insoluble salts formed by the reaction of acids and bases or other electrolytes ... 

Now that you have learned about some of the properties of water, solutes, and colloids, you can understand why it is sometimes said that the chemistry of water is the chemistry of solutions. As you have discovered in this chapter, the physical properties of water make it a imique and important substance. Its ability to form solutions gives it an essential role in every aspect of life, including the reactions of acids and bases. As you will see, in these reactions, water is a subtle but important partner. 

The reactions of acids and bases are central to the chemistry of living systems, the environment, and many important industrial processes. Table 14.1 shows the top ten industrial chemicals produced in the United States in 1994. Not surprisingly, acids and bases make up half of the top ten. 

In Chapter 4 we defined a Brpnsted acid as a snbstance capable of donating a proton, and a Brpnsted base as a substance that can accept a proton. These definitions are generally suitable for a discussion of the properties and reactions of acids and bases. 

The equilibrium constant of a reversible dissociation is called the dissociation constant. The term dissociation is also applied to ionization reactions of acids and bases in water for example HCN + H2O H3O+ + CN-which is often regarded as a straightforward dissociation into ions HCN H+ + CN-... 

The properties and reactions of acids and bases are central to our study of organic chemistry. We need to consider exactly what is meant by the terms add and base. Most people would agree that H2SO4 is an acid and NaOH is a base. Is BF3 an acid or a base Is ethylene (H2C=CH2) an acid or a base To answer these questions, we need to understand the three different definitions of acids and bases the Arrhenius definition, the Brpnsted-Lowry definition, and the Lewis definition. 

I recommend, though, simply treating reactions of metal carbonates to make a salt and water (and carbon dioxide) as a special case and not mixing them up with a general discussion of reactions of acids and bases. Readers may find this in contrast with more traditional textbooks. 

Hulanicki A (1987) Reactions of Acids and Bases in Analytical Chemistry. Chichester Ellis Horwood. Inczedy J (1973) Analytical Applications of Complex Equilihria. Chichester Ellis Horwood. lUPAC (1998) In Inczedy J, Lengyel T, and Ure AM (eds.) Compendium of Analytical Nomenclature. Oxford Blackwell Science. 

It might be expected that acid-base equilibria would show particularly simple behaviour in completely aprotic solvents, such as hydrocarbons and their halogen derivatives, in which interactions with the solvent are reduced to a minimum. In such systems it is of course impossible to observe the reaction of acids and bases with the solvent, and it is necessary to investigate a solution containing two acid-base pairs, sometimes with the addition of a third to act as an indicator. However, there are... 

The following molecular equations all represent neutralization reactions of acids and bases. These reactions will be discussed further in Chapter 9. Write each equation in total ionic form, identify the spectator ions, then write the net ionic equation. Water is the only substance that does not dissociate. What do you notice about all the net ionic equations ... 

The neutrahzation reaction of acids and bases is used in a process called titration to analyze acids and bases. During a typical titration, a base solution of known concentration is added slowly to an acid solution of unknown concentration. The titration is stopped at the endpoint when a color change occurs in an indicator. The volumes of acid and base required are used to calculate the acid concentration. 

Study this example carefully. It is very important to be able to write balanced equations for reactions of acids and bases. You must be able to identify conjugate acids and conjugate bases. 

One of the most important reactions of acids and bases is neutralization, first introduced in Qiapter 7. When an acid and a base are mixed, the H aq) from the acid combines with the OH ( q ) from the base to form H20(l). For example, consider the reaction between hydrochloric acid and potassium hydroxide. 

Reactions of Acids and Bases Neutralization reactions are common in our everyday lives. Antacids, for example, are bases fhaf read with acids from fhe stomach to alleviate heartburn and sour stomach. Acid-metal and acid-metal oxide reactions show the corrosive nature of acids. In both of these reactions, the acid dissolves the metal or the metal oxide. Some of the effects of fhese kinds of reactions can be seen in the damage to building materials caused by acid rain. Since acids dissolve metals and metal oxides, any building materials composed of fhese substances are susceptible to acid rain. 

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