Arrhenius acid-base theory

Arrhenius acid-base theory - Arrhenius developed the theory of the electrolytic dissociation (1883-1887). According to him, an acid is a substance which delivers hydrogen ions to the solution. A base is a substance which delivers hydroxide ions to the solution. Accordingly, the neutralization reaction of an acid with a base is the formation of water and a salt. It is a so-called symmetrical definition because both, acids and bases must fulfill a constitutional criterion (presence of hydrogen or hydroxide) and a functional criterion (to deliver hydrogen ions or hydroxide ions). The theory could explain all of the known acids at that time and most of the bases, however, it could not explain the alkaline properties of substances like ammonia and it did not include the role of the solvent. -> Sorensen (1909) introduced the -> pH concept. 

The pH of a solution with a hydrogen ion concentration of 0.003 M is between what two whole numbers (Table 15.4) Which is more acidic, tomato juice or blood (Table 15.5) Use the three acid-base theories (Arrhenius, Brpnsted-Lowiy, and Lewis) to define an acid and a base. 

In the previous sections, you learned about three acid-base theories Arrhenius, Bronsted-Lowry, and Lewis. The Bronsted-Lowry theory is especially useful for describing acid-base reactions that take place in aqueous solutions. This section will use the Bronsted-Lowry description to explore reactions between acids and bases. 

This theory was a milestone in the development of acid-base concepts it was the first to define acids and bases in terms other than that of a reaction between them and the first to give quantitative descriptions. However, the theory of Arrhenius is far more narrow than both its predecessors and its successors and, indeed, it is the most restrictive of all acid-base theories. 

From our previous treatment of the Arrhenius, Bransted and Lewis acid-base theories, the importance of the choice between the divergent solvent types clearly appeared if we now confine ourselves to solvents to which the proton theory in general is applicable, this leads to a classification of eight classes as already proposed by Bronsted35,36 (Table 4.3). 

Our goal in this chapter is to help you understand the equilibrium systems involving acids and bases. If you don t recall the Arrhenius acid-base theory, refer to Chapter 4 on Aqueous Solutions. You will learn a couple of other acid-base theories, the concept of pH, and will apply those basic equilibrium techniques we covered in Chapter 14 to acid-base systems. In addition, you will need to be familiar with the log and 10 functions of your calculator. And, as usual, in order to do well you must Practice, Practice, Practice. 

The Arrhenius acid-base theory is insufficient to explain the acidic or basic properties of some substances, such as SO2 and NH3, since these don t have H" and OH ions in their structures. For these molecules, another theory must be applied, since the Arrhenius acid-base theory can only be applied to aqueous solutions. 

Feb. 19,1859, Wijk, Sweden - Oct. 2,1927, Stockholm, Sweden). Arrhenius developed the theory of dissociation of electrolytes in solutions that was first formulated in his Ph.D. thesis in 1884 Recherches sur la conductibilit galvanique des dectrolytes (Investigations on the galvanic conductivity of electrolytes). The novelty of this theory was based on the assumption that some molecules can be split into ions in aqueous solutions. The - conductivity of the electrolyte solutions was explained by their ionic composition. In an extension of his ionic theory of electrolytes, Arrhenius proposed definitions for acids and bases as compounds that generate hydrogen ions and hydroxyl ions upon dissociation, respectively (- acid-base theories). For the theory of electrolytes Arrhenius was awarded the Nobel Prize for Chemistry in 1903 [i, ii]. He has popularized the theory of electrolyte dissociation with his textbook on electrochemistry [iv]. Arrhenius worked in the laboratories of -> Boltzmann, L.E., -> Kohlrausch, F.W.G.,- Ostwald, F.W. [v]. See also -> Arrhenius equation. 

The first acid-base theory that we will discuss is the Arrhenius Theory. Proposed by a Swedish chemist named Svante Arrhenius in 1887, this was the first acid-base theory, and it remains the most specific or limiting. According to the Arrhenius Theory, an acid is a substance that releases H+ ions in aqueous solution. This would explain why the acids that you are familiar with, such as HC1 and H2S04, have hydrogen in their formulas. Arrhenius bases are only those substances that release OH ions in aqueous solutions. This would include common bases, such as NaOH and KOH, but would exclude other substances, such as NH3, that also have the ability to neutralize acids. 

Arrhenius in 1887 was the first person to give a definition of an acid and a base. According to him, an acid is one that gives rise to excess of in aqueous solution, whereas a base gives rise to excess of OH in solution. This was modified by Bronsted-Lowry in 1923 such that a proton donor was defined as an acid and a proton acceptor as a base. They also introduced the familiar concept of the conjugate acid-base pair. The final refinement to the acid-base theory was completed by Lewis in 1923, who extended the concept that acid is an acceptor of electron pairs while base is a donor of electron pairs. 

Skill 10.1 Analyzing acids and bases according to acid-base theories (i.e., Arrhenius, Bronsted-Lowry, Lewis)... 

Sumfleth [6] also states, that the idea of proton transfer may be learned by students but cannot be applied in a new context. Sumfleth and Geisler [7] show that students accept the Broensted definition, but bases are interpreted mostly based on the Arrhenius idea. Therefore, the knowledge about Broensteds concept cannot be transferred to new contexts. Sumfleth states that most students cannot really apply acid-base theories, especially at the advanced levels. This is also evident for students who have chosen chemistry as their major . 

The Arrhenius theory satisfactorily explains the behavior of many acids and bases. However, a substance such as ammonia, NH3, has basic properties but cannot be an Arrhenius base, because it contains no OH. The Brnnsted-Lowry theory explains this mystery and gives us a broader view of acid-base theory by considering the central role of the solvent in the dissociation process. 

Several acid-base theories have been proposed to explain or classify acidic and basic properties of substances. You are probably most familiar with the Arrhenius theory, which is applicable only to water. Other theories are more general and are applicable to other solvents. We describe the common acid-base theories here. 

A major problem with Arrhenius s acid-base theory is that some substances, like ammonia, produce basic solutions and react with acids, but do not contain hydroxide ions. In 1923 Johannes Bronsted, a Danish chemist, and Thomas Lowry, an English chemist, independently proposed a new way to define acids and bases. An acid donates hydrogen ions (also called a proton donor) a base accepts hydrogen ions (also called a proton acceptor). These definitions not only explain all the acids and bases covered by Arrhenius s theory, they also explain the basicity of ammonia and ions such as carbonate, and phosphate, P04 ... 

Acid/Base Theories Imagine that you are the Danish chemist Johannes Bronsted. The year is 1923, and you have formulated a new theory of acids and bases. Write a letter to Swedish chemist Svante Arrhenius in which you discuss the differences between your theory and his and point out the advantages of yours. 

Arrhenius acids and bases represent a subset of a more generalized model of acid-base theory known as solvent theory. In solvent theory, an acid is defined as any substance that increases the concentration of the cationic species that results from autoionization of the solvent, whereas a base increases the concentration of the anionic species from autoionization. Table 14.1 lists the ion products for some of the more common solvents that undergo autoionization. 

The Arrhenius theory was the first modern acid-base theory developed. In this theory, an acid is a substance that, when dissolved in water, yields (Tiydro-gen) ions, and a base is a substance that, when dissolved in water, yields OH (hydroxide) ions. HCl(g) can be considered as a typical Arrhenius acid, because when this gas dissolves in water, it ionizes (forms ions) to give the ion. (Chapter 6 is where you need to go for the riveting details about ions.)... 

Lewis proposed his stiU broader and more useful definition of acids and bases in the late 1920s and early 1930s. Classifying acids as electron-pair acceptors and bases as electron-pair donors, he thereby liberated acid—base theory entirely from its former dependence on the presence of hydrogen. The advantage of the Lewis definition is that a larger number of reactions can be classified as acid-base than under either the Arrhenius or Bronsted-Lowry definitions. The classic example used to demonstrate the more general nature of the Lewis definition is the gas-phase reaction between boron trifluoride and ammonia, as represented in Equation (4.1) ... 

Hydrogen was recognized as the essential element in acids by H. Davy after his work on the hydrohalic acids, and theories of acids and bases have played an important role ever since. The electrolytic dissociation theory of S. A. Arrhenius and W. Ostwald in the 1880s, the introduction of the pH scale for hydrogen-ion concentrations by S. P. L. Sprensen in 1909, the theory of acid-base titrations and indicators, and J. N. Brdnsted s fruitful concept of acids and conjugate bases as proton donors and acceptors (1923) are other land marks (see p. 48). The di.scovery of ortho- and para-hydrogen in 1924, closely followed by the discovery of heavy hydrogen (deuterium) and... 

The Arrhenius concept was of basic importance because it permitted quantitative treatment of a number of acid-base processes in aqueous solutions, i.e. the behaviour of acids, bases, their salts and mixtures of these substances in aqueous solutions. Nonetheless, when more experimental material was collected, particularly on reaction rates of acid-base catalysed processes, an increasing number of facts was found that was not clearly interpretable on the basis of the Arrhenius theory (e.g. in anhydrous acetone NH3 reacts with acids in the absence of OH- and without the formation of water). It gradually became clear that a more general theory was needed. Such a theory was developed in 1923 by J. N. Br0nsted and, independently, by T. M. Lowry. 

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