Bronsted—Lowry acids and bases

The general words acid and base usually mean a Bronsted-Lowry acid and Bronsted-Lowry base. 

Chemical terms such as anion and cation may be unfamiliar to most nonscientists, but acid has found a place in everyday language. Commercials advertise the latest remedy for the heart-bum caused by excess stomach acid. The nightly news may report the latest environmental impact of acid rain. Wine lovers know that wine sours because its alcohol has turned to acid. Acid comes from the Latin word acidus, meaning sour, because when tasting compounds was a routine method of identification, these compounds were sour. 

In Chapter 2, we will concentrate on two definitions of acids and bases the Brpnsted-Lowry definition, which describes acids as proton donors and bases as proton acceptors, and the Lewis definition, which describes acids as electron pair acceptors and bases as electron pair donors. 

The Br0nsted-Lowry definition describes acidity in terms of protons positively charged hydrogen ions, 

A Brpnsted-Lowry acid must contain a hydrogen atom. This definition of an acid is often familiar to students, because many inorganic acids in general chemistry are Br0nsted-Lowry acids. The symbol H-A is used for a general Br0nsted-Lowry acid. 

---

Just as a quarterback and receiver act as a pair, Bronsted-Lowry acid and bases act as pairs (Figure 13.1). Acids and bases are... 

The best way to spot Bronsted-Lowry acids and bases is to keep careful track of hydrogen ions in a chemical equation. Consider, for example, the dissociation of the base sodium carbonate in water. Note that although sodium carbonate is a base, it doesn t contain a hydroxide ion. 

For the remainder of this book, when we speak of acids and bases, we are speaking of Bronsted-Lowry acids and bases. 

The key to solving acid-base equilibrium problems is to think about the chemistry—that is, to consider the possible proton-transfer reactions that can take place between Bronsted-Lowry acids and bases. 

For each of the following reactions, identify the Bronsted-Lowry acids and bases ... 

Another significant difference between definitions is that Bronsted-Lowry acids and bases need not be molecular substances. There are a variety of reactions in which ions donate or accept protons. In the sample below, note how the cyanide ion (CN-) acts as a base by accepting a proton and the bicarbonate ion (HC03 ) acts as an acid by donating a proton ... 

Before continuing on to the last definition of acids and bases, it will be helpful to consider the definitions for strong and weak acids within the context of the Bronsted-Lowry model of acids and bases. The definitions are really an extension of the Arrhenius ideas. In the Arrhenius definitions, strong acids and bases were those that ionize completely. Most Bronsted-Lowry acids and bases do not completely ionize in solution, so the strengths are determined based on the degree of ionization in solution. For example, acetic acid, found in vinegar, is a weak acid that is only about 1 percent ionized in solution. That means that when acetic acid, HC2H302, is placed in water, the reaction looks like ... 

The Lewis concept deals with the behavior of electron pairs in chemical reactions. The same electron pairs we looked at when we discussed molecular geometry (see Chapter 7) can be involved in many reactions. Substances that can form a covalent bond by accepting an electron pair from another substance are known as Lewis acids. Substances that can form a covalent bond by donating an electron pair to another substance are known as Lewis bases. Be careful that you don t mix these up with the Bronsted-Lowry acids and bases. It is easy to do since the words donate and accept are used, except they are associated with the opposite species (Bronsted-Lowry acids donate protons, while Lewis acids accept electron pairs). 

Bronsted-Lowry acids donate protons in solution. Bronsted-Lowry bases accept protons in solution. The definitions for Bronsted-Lowry acids and bases are more broad and allow for the consideration of many more substances than either of the other two definitions. 

A vast generalization beyond the Bronsted—Lowry acids and bases concepts is the concept of a Lewis29 base (an electron pair donor) and a Lewis acid (an electron pair acceptor). This concept has been used extensively in all branches of chemistry. In physical organic chemistry, quantities of the type pA = —logio[A] have used extensively to study reactivities—for example, in the Hammett equation. 

Bronsted-Lowry acids and bases are also classified according to the extent that they react with solvents (H20). Commonly, they are classified into strong acids and bases and weak acids and bases. Strong acids are 100% dissociated in water. For example, hydrochloric acid (HC1), a strong acid, dissociates as follows ... 

Boundary potential, E, The resultant of two potentials that develop at the surfaces of a glass membrane electrode. Bronsted-Lowry acids and bases An acid of this type is defined as a proton donor and a base as a proton acceptor the loss of a proton by an acid results in the formation of a species that is a potential proton acceptor, or conjugate base of the parent acid. Buffer capacity The number of moles of strong acid (or strong base) needed to alter the pH of 1.00 L of a buffer solution by 1.00 unit. 

Arrhenius acids and bases are also Bronsted-Lowry acids and bases the reverse is not true. 

Identify the Bronsted-Lowry acids and bases in these reactions and group them into conjugate acid-base pairs. 

Bronsted-Lowry Acids and Bases Proton donors and acceptors... 

The Bronsted-Lowry system allows us to describe all of these reactions as acid-base Objective 26 reactions. They are repeated below, with the Bronsted-Lowry acids and bases labeled. 

Identify the Bronsted-Lowry acid and base in each of the following equations. 

---