Lowry-Bronsted

Acids and bases are defined as proton donors and acceptors respectively. This now includes a much wider array of compounds as possible bases. In the following reaction, which is the acid and which is 

Note that the reagents are gases, and that the product is a solid, i.e. the reaction is not being performed in solution. The hydrogen chloride is still considered to be the acid, because it donates a proton. The ammonia molecule is now considered to be the base, because it accepts a proton in this reaction. Why would the ammonia molecule not be considered a base under the Arrhenius definition  

The ammonia molecule does not produce a hydroxide ion. What would have been the position if the reaction had been carried out in the aqueous phase  

In the aqueous phase, the ammonia molecule would have reacted with a water molecule to form an ammonium ion and a hydroxide ion. Write an equation for this reaction. 

If ammonia had been allowed to react with hydrogen chloride in the aqueous phase, then it would have fallen within the Arrhenius definition of an acid/base reaction. Notice that it is the water molecule that is central to the Arrhenius definition, and this is one of the main reasons why it is of little use in conventional organic chemistry. Similarly, because the Bronsted-Lowry definition does not depend on water, but only upon the presence of two compounds of complementary properties, it is this definition that is of more use to organic chemists. 

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A useful definition of acids and bases is that independently introduced by Johannes Bronsted (1879-1947) and Thomas Lowry (1874-1936) in 1923. In the Bronsted-Lowry definition, acids are proton donors, and bases are proton acceptors. Note that these definitions are interrelated. Defining a base as a proton acceptor means an acid must be available to provide the proton. For example, in reaction 6.7 acetic acid, CH3COOH, donates a proton to ammonia, NH3, which serves as the base. 

A Bronsted-Lowry acid is a substance that donates a proton (H+), and a Bronsted-Lowry base is a substance that accepts a proton. (The name proton is often used as a synonym for hydrogen ion, H+, because loss of the valence electron from a neutral hydrogen atom leaves only the hydrogen nucleus— a proton.) When gaseous hydrogen chloride dissolves in water, for example, a polar HC1 molecule acts as an acid and donates a proton, while a water molecule acts as a base and accepts the proton, yielding hydronium ion (H30+) and chloride ion (Cl-). 

The Lewis definition of acids and bases is broader and more encompassing than the Bronsted-Lowry definition because it s not limited to substances that donate or accept just protons. A Lewis acid is a substance that accepts an electron pair, and a Lewis base is a substance that donates an electron pair. The donated electron pair is shared between the acid and the base in a covalent bond. 

The Lewis definition of a base as a compound with a pair of nonbonding electrons that it can use to bond to a Lewis acid is similar to the Bronsted-Lowry definition. Thus, H20, 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, H30+. 

Like other Bronsted-Lowry acids discussed in Section 2.7, carboxylic acids dissociate slightly in dilute aqueous solution to give H30+ and the corresponding carboxylate anions, RC02. The extent of dissociation is given by an acidity constant, Ka. 

Bronsted-Lowry acid (Section 2.7) A substance that donates a hydrogen ion (proton H + ) to a base. 

Conjugate acid (Section 2.7) The product that results from protonation of a Bronsted-Lowry base. 

Backbone (protein), 1028 Backside displacement. reaction and.363-364 von Baeyer, Adolf, 113 Baeyer strain theory, 113-114 Bakelile, structure of, 1218 Banana, esters in, 808 Barton, Derek, H. R., 389 Basal metabolic rate, 1169 Basal metabolism. 1169-1170 Base, Bronsted-Lowry, 49 Lewis, 57, 59-60 organic, 56-57 strengths of, 50-52 Base pair (DNA), 1103-1105 electrostatic potential maps of. 

Bronsted-Lowry acid, 49 conjugate base of, 49 strengths of, 50-52 Bronsted-Lowry base, 49 conjugate acid of, 49 strengths of, 50-52 Brown, Herbert Charles. 223 Butacetin, structure of. 833 1,3-Butadiene, 1,2-addition reactions of, 487-489... 

The model of acids and bases used in this chapter is a somewhat more general one developed independently by Johannes Bronsted (1879-1947) in Denmark and Thomas Lowry (1874-1936) in England in 1923. The Bronsted-Lowry model focuses on the nature of acids and bases and the reactions that take place between them. Specifically, it considers that—... 

The species shown in red, HB and HA, act as Bronsted-Lowry acids in the forward and reverse reactions, respectively A and B (blue) act as Bronsted-Lowry bases. (We will use this color coding consistently throughout the chapter in writing Bronsted-Lowry acid-base equations.)... 

In connection with the Bronsted-Lowry model, there are some terms that are used frequently. 

A wide variety of solutes behave as weak acids that is, they react reversibly with water to form H30+ ions. Using HB to represent a weak acid, its Bronsted-Lowry reaction with water is... 

Molecules. As pointed out in Chapter 4, there are many molecular weak bases, including the organic compounds known as amines. The simplest weak base is ammonia, whose reversible Bronsted-Lowry reaction with water is represented by the equation... 

Bronsted-Lowry acids (left column) can be divided into three categories ... 

Classify a species as a Bronsted-Lowry acid or base and explain by a net ionic equation. (Examples 13.1,13.4,13.10 Problems 1-12) Questions and Problems assignable in OWL 2,4,12,34,64... 

As pointed out in Chapter 13, strong acids ionize completely in water to form H30+ ions strong bases dissolve in water to form OH- ions. The neutralization reaction that takes place when any strong acid reacts with any strong base can be represented by a net ionic equation of the Bronsted- Lowry type ... 

The reaction between solutions of hydrochloric acid and ammonia can be represented by the Bronsted- Lowry equation ... 

This more general view of acids and bases is named the Bronsted-Lowry theory after the two scientists who proposed it, J. N. Brpnsted and T. M. Lowry. 

The Bronsted-Lowry expression for acid-base equilibria (see Section 2.4)... 

On the above basis it is, in principle, unnecessary to treat the strength of bases separately from acids, since any protolytic reaction involving an acid must also involve its conjugate base. The basic properties of ammonia and various amines in water are readily understood on the Bronsted-Lowry concept. 

The phenomenon of salt hydrolysis may be regarded as a simple application of the general Bronsted-Lowry equation... 

The equations can be readily expressed in a somewhat more general form when applied to a Bronsted-Lowry acid A and its conjugate base B ... 

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