The Br0nsted-Lowry Theory

The Br0nsted-Lowry theory expands the definition of acids and bases to allow us to explain n ch more ol solution chemistry. For example, the Brpnsted-Lowry theory allows us to explain why a solution af ammonium nitrate tests acidic and a solution of potassium acetate tests basic. Most of the substances that we cofcider acids in the Arrhenius theory are also acids in the Brpnsted-Lowry theory, and the same is true of bases. Injboth theories, strong acids are those that react completely with water to form ions. Weak acids ionize only slightly. We can now explain this partial ionization as an equilibrium reaction of the weak acid, the ions, and the w ater. A similar statement can be made about weak bases  

The HC2H3O2 is an acid because it denotes its proton to the H2O to form C2H302 and H3p+. The H2O is a base because it accepts that proton. But this is an equilibrium reaction, and C2H302 reacts wto H3O+ to form HC2H3O2 and H2O. The C2H302 is a base because it accepts the proton from H3O+ the H3O+ is an acid because it donates a proton. H3O+ is called the hydronium ion. It is the combination of a pro  

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The acid on the left of this equation is related to the base on the right they are said to be conjugates of each other. The HC2H3O2 is the conjugate acid of the base C2H302. Similarly, H2O is the conjugate base of H3O+. Conjugate differ in each case by /7+. 

EXAMPLE 17.1. Write an equilibrium equation for the reaction of NH3 and H2O, and label each of the conjugate acids and bases. 

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THE PROTOLYSIS OF ACIDS. STRENGTHS OF ACIDS AND BASES It is of interest to examine the processes which take place when an acid is dissolved in a solvent, first of all in water. According to the Br0nsted-Lowry theory this dissolution is accompanied by a protolytic reaction, in which the solvent (water) acts as a base. To elucidate these processes, let us examine what happens if a strong acid (hydrochloric acid) and a weak acid (acetic acid) undergo protolysis. 

This expression can easily be derived from the case of ammonia. In the view of the Br0nsted-Lowry theory the dissociation of ammonium hydroxide is more properly the reaction of ammonia with water. ... 

INTERPRETATION OF OTHER ACID-BASE REACTIONS WITH THE BR0NSTED-LOWRY THEORY As already outlined, the great advantage of the Brensted-Lowry theory lies in the fact that any type of acid-base reaction can be interpreted with the simple reaction scheme... 

In contrast to the Br0nsted-Lowry theory, which emphasizes the proton as the principal species in acid-ba.se reactions, the definition proposed by Lux and extended by Floods describes acid-base behavior in terms of the oxide ion. This acid-base concept was advanced to treat nonprotonic systems which were not amenable to the Br0nsted-Lowry definition. For example, in high-temperature inorganic melts, reactions such as the following take place ... 

Lux—Flood Definition In contrast to the Br0nsted-Lowry theory, which emphasizes the proton as the... 

The Br0nsted-Lowry theory assumes a transfer of protons from an acid to a base, i.e., conjugate pairs. 

In the same year the English chemist T.M. Lowry published a paper setting forth some similar ideas without producing a definition in a later paper Lowry himself points out that Brpnsted deserves the major credit, but the concept is still widely known as the Br0nsted-Lowry theory. 

The Br0nsted-Lowry theory conjugate acid-base pairs... 

An even more general theory of acids and bases was given by the American chemist G. N. Lewis in 1923. In this theory, an acid is an electron acceptor and a base is an electron donor. This is a more general theory than the Br0nsted-Lowry theory, because it allows the acid-base classification to be applied to reactions in which neither H (aq) nor OH (aq) play a role, or even to reactions in which there is no solvent. For example, the following are acid-base reactions in the Lewis theory... 

In Chapter 5 we saw that, in terms of the Br0nsted-Lowry theory, acid-base reactions involve proton transfer. Another large and important group of chemical reactions, particularly in aqueous solutions, involves electron transfer these are referred to as oxidation-reduction (or redox) reactions. Redox reactions are involved (1) in photosynthesis, which releases oxygen into the Earth s atmosphere (2) in the combustion of fuels, which is responsible for rising concentrations of atmospheric carbon dioxide (3) in the formation of acid precipitation and (4) in many chemical reactions in Earth sediments. 

The Br0nsted-Lowry theory of acids and bases involves the transfer of protons or hydrogen ions within an aqueous solution. An acid is defined as a molecule or ion that acts as a proton donor and a base is defined as a molecule or ion that acts as a proton acceptor. For example, when hydrogen chloride gas is dissolved in water it reacts to form hydrochloric acid. The following equilibrium is established ... 

However, the Lewis theory is more general than the Br0nsted-Lowry theory some reactions are classified as acid-base reactions under the Lewis definitions that are not regarded as acid-base reactions under the Br0nsted-Lowry theory. Therefore the terms Lewis acid and Lewis base are often reserved for species which are Lewis acids and bases, but which are not Br0nsted-Lowry acids and bases. 

The Br0nsted-Lowry theory can be applied to solvents other than water. Ammonia, like water, is amphiprotic and can behave as a Br0nsted-Lowry acid or base ... 

The shortcomings of the Arrhenius theory led chemists to seek other explanations for the nature of acids and bases. The Br0nsted-Lowry theory was introduced independently in 1923 by the Danish chemist Johannes Nicolaus Brqnsted and the English chemist Thomas Martin Lowry, stating that any compound that can transfer a proton to any other compound is an acid, and the compound that accepts the proton is a base. Their theory explained the behaviour of all of the acids and bases covered by the Arrhenius theory, but also was able to resolve some of the problems with that theory. That is, they were able to explain why some salts are acidic and basic (due to salt hydrolysis) and why no free protons are found in the solutions of some acids. 

By the Br0nsted-Lowry theory, water can be either an acid or a base. Can water be a Lewis acid A Lewis base Explain. 

Our principal interest in acid-base chemistry is in aqueous solutions, where the Br0nsted-Lowry theory prevails. The balance of this chapter is limited to the proton-transfer concept of acids and bases. 

Bases are much the same in the Lewis theory and in the Brpnsted-Lowry theory, because in the Br0nsted-Lowry theory a base must donate a pair of electrons in order to accept a proton. 

According to the Br0nsted-Lowry theory, a conjugate acid-base pair consists of molecules or ions related by the loss of one by an acid, and the gain of one by a... 

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