Acids Brpnsted-Lowry definition

Section 1 13 According to the Brpnsted-Lowry definitions an acid is a proton donor and a base is a proton acceptor... 

This IS a very useful relationship You should practice writing equations according to the Brpnsted-Lowry definitions of acids and bases and familiarize yourself with Table 1 7 which gives the s of various Br0n sted acids... 

At the microscopic level, the Arrhenius theory defines acids as substances which, when dissolved in water, yield the hydronium ion (H30+) or H+(aq). Bases are defined as substances which, when dissolved in water, yield the hydroxide ion (OH). Acids and bases may be strong (as in strong electrolytes), dissociating completely in water, or weak (as in weak electrolytes), partially dissociating in water. (We will see the more useful Brpnsted-Lowry definitions of acids and bases in Chapter 15.) Strong acids include ... 

A particularly important concept in chemistry is that associated with proton loss and gain, i.e. acidity and basicity. Acids produce positively charged hydrogen ions H+ (protons) in aqueous solution the more acidic a compound is, the greater the concentration of protons it produces. In water, protons do not have an independent existence, but become strongly attached to a water molecule to give the stable hydronium ion H3O+. In the Brpnsted-Lowry definition ... 

Brpnsted-Lowry definition does not differ appreciably from the Arrhenius definition of hydrogen ions (acids) and hydroxide ions (bases) ... 

In addition to Arrhenius acids and bases, the Brpnsted-Lowry definition includes bases that have no hydroxide ions, yet can accept protons. Consider the following examples of acids donating protons to bases. NaOH is a base under either the Arrhenius or Brpnsted-Lowry definition. The other three are Brpnsted-Lowry bases but not Arrhenius bases, because they have no hydroxide ions. 

Brpnsted-Lowry Definition Acids are proton (H1+) donors. Bases are proton (H1+) acceptors. 

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. 

How does the Brpnsted-Lowry definition of an acid differ from the Arrhenius definition... 

The correct answer is (C). Bases in this reaction would be considered the substances that are accepting protons (Brpnsted-Lowry definition). In the forward reaction, H,0 receives a hydrogen to become a hydronium ion. In the reverse reaction, CN" receives a proton to become HCN. HCN donates a proton, which makes it an acid. 

A more general definition of acid-base equilibrium in molecular solvents was proposed independently by Brpnsted and Lowry, who extended the term base . According to them, the acid is a donor of protons, and they defined a base only as an acceptor of H+. According to the Brpnsted-Lowry definition, the dissociation of an acid results in the formation of a proton and a conjugate base ... 

Of course, protons cannot exist as free particles in molecular solvents they should react with the solvent molecules, and such an interaction in aqueous solutions results in the formation of H5Oj (H+-2H20 or [H20--H--0H2]+) particles. Similarly, hydroxide ions in aqueous solutions exist as H302 (OH2- -OH-). The stronger the acid Ai compared to the acid A2, the more complete is the shift of reaction (1.1.6) to the right. The Brpnsted-Lowry definition thus extends the term acid-base interaction to reactions accompanied with proton transfer from one base to another. For example,... 

An obvious advantage of the Brpnsted-Lowry definition compared with TED is the fact that acid-base interaction reaches an equilibrium between two conjugate pairs in a solvent. When this definition was formulated it considered only different protolytic media as appropriate solvents, whose dissociation process can be described by the following scheme ... 

Usually, definitions of acids and bases are necessary for the classification of different kinds of chemical reactions, i.e. for dividing them into acid-base and other ones. For example, the Brpnsted-Lowry definition divides reactions into acid-base, which are characterized by redistribution of protons, and other ones. The wider Lewis definition makes the division of reactions into acid-base and redox ones, meaning that in the former case there is redistribution of electron density on account of electron pairs, and the latter case concerns reactions with the transfer of single electrons. Since chemistry concerns just the redistribution of electrons of external shells, we can classify all chemical reactions as acid-base ones by the Usanovitch definition. 

All nucleophiles are bases (1). In fact, within the definition of Lewis (2), nucleophilicity is basicity. Following Ingold (3), however, physical-organic chemists have normally used the Brpnsted-Lowry definition (4, 5) of bases as affinity for protons. Likewise, nucleophilicity referred to affinity for nuclei of other elements, most often carbon (3). Another classification reserves basicity, and its counterpart acidity, for equilibrium measurements, while nucleophilicity and its counterpart electrophilicity refer to rate measurements (6). The terms carbon basicity and hydrogen nucleophilicity have been employed (7-9). This classification does not seem to have gained much acceptance. 

Understand the Brpnsted-Lowry definitions of an acid and a base discuss how water can act as a base or as an acid and how an acid-base reaction is a proton-transfer process involving two conjugate acid-base pairs, with the stronger acid and base forming the weaker base and acid ( 18.3) (SPs 18.4, 18.5) (EPs 18.24-18.39)... 

The definitions of acid and base that we use now were provided by Brpnsted and Lowry in 1923. In the Br0nsted-Lowry definitions, an acid is a species that donates a proton, and a base is a species that accepts a proton. (Remember that positively charged hydrogen ions are also called protons.) In the following reaction, hydrogen chloride (HCl) meets the Brpnsted-Lowry definition of an acid because it donates a proton to water. Water meets the definition of a base because it accepts a proton from HCl. Water can accept a proton because it has two lone pairs. Either lone pair can form a covalent bond with a proton. In the reverse reaction, H3O is an acid because it donates a proton to CF, and CF is a base because it accepts a proton from H30. ... 

The Brpnsted-Lowry definition of acidity discussed in the previous four sections encompasses all compounds containing hydrogen. Of even more use, however, is the Lewis definition of acids and bases, which is not limited to compounds that gain or lose protons. A Lewis acid is a substance that accepts an electron pair, and a Lewis base is a substance that donates an... 

To discuss acid-base catalysis, it is helpful to recall the definitions of acids and bases. In the Brpnsted-Lowry definition, an acid is a proton donor and a base is a proton acceptor. The concept of general acid-base catalysis depends on donation and acceptance of protons by groups such as the imidazole, hydroxyl, carboxyl, sulfhydryl, amino, and phenolic side chains of amino acids all these functional groups can act as acids or bases. The donation and acceptance of protons gives rise to the bond breaking and re-formation that constitute the enzymatic reaction. 

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. 

Since a hydrogen ion and a proton are identical, what differences exist between the Arrhenius and Brpnsted-Lowry definitions of an acid (Table 15.1)... 

In the aqueous system, the Brpnsted-Lowry definitions of acids and bases are of general applicability. A Brpnsted acid a proton donor. Acidic oxides react with water to produce oxonium ions in solution, e.g. 

Acid (Arrhenius definition) a substance that produces hydrogen ions, H, (hydronium ion, H30 ) when it dissolves in water. (4.4 and 16.1) (Brpnsted-Lowry definition) the species (molecule or ion) that donates a proton to another species in a proton-transfer reaction. (4.4 and 16.2)... 

Acid According to the Arrhenius definition, a substance that ionizes in water to produce protons. According to the Brpnsted-Lowry definition, a substance that donates a proton to some other substance. According to the Lewis definition, an electron-pair acceptor. 

The usefulness of the Brpnsted-Lowry definition lies in its ability to handle any protonic solvent such as liquid ammonia or sulfuric acid ... 

You have reviewed the Brpnsted-Lowry definition of acids and bases and the meanings of pH and p a- You have learned to identify the most acidic hydrogen atoms in a molecule based on a comparison of p a values. You will see in many cases that Brpnsted-Lowry acid-base reactions either initiate or complete an organic reaction, or prepare an organic molecule for further reaction. The Lewis definition of acids and bases may have been new to you. However, you will see over and over again that Lewis acid-base reactions which involve either the donation of an electron pair to form a new covalent bond or the departure of an electron pair to break a covalent bond are central steps in many organic reactions. The vast majority of organic reactions you will study are either Brpnsted-Lowry or Lewis acid-base reactions. 

A further important concept related to electronegativity and polarity is that of acidity and basicity. We ll see, in fact, that much of the chemistry of organic molecules can he explained hy their acid-hase behavior. You may recall from a course in general chemistry that there are two frequently used definitions of acidity the Brensted-Lowry definition and the Lewis definition. We ll look at the Brpnsted-Lowry definition in this and the next three sections and then discuss the Lewis definition in Section 2.11. 

The Lewis definition of a base—a compound with a pair of nonhonding electrons that it can use in bonding to a Lewis acid—is similar to the Brpnsted-Lowry definition. Thus, H2O, with its two pairs of nonbonding electrons on oxygen, acts as a Lewis base by donating an electron pair to an H+ in forming the hydronium ion, HsO" ". 

An acid is a species that can lose a proton (the Brpnsted-Lowry definition). When an acid loses a proton (H ), it forms its conjugate base. When the proton comes off the acid, the conjugate base retains the electron pair that attached the proton to the acid. 

A second, more widely apphcable definition of acids and bases, called the Brpnsted-Lowry definition, was introduced in 1923. This definition focuses on the transfer ofH ions in an acid-base reaction. Since an H ion is a proton—a hydrogen atom without its electron—this definition focuses on the idea of a proton donor and a proton acceptor ... 

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