Arrhenius theory of acidity

Thus far, we have used the Arrhenius theory of acids and bases (Secs. 6.4 and 7,3) in which acids are defined as hydrogen-containing compounds that react with bases. Bases are compounds containing OH" ions or that form OH- ions when they react with water. Bases react with acids to form salts and water. Metallic hydroxides and ammonia are the most familiar bases to us. 

According to the Arrhenius theory of acids and bases, the acidic species in water is the solvated proton (which we write as H30+). This shows that the acidic species is the cation characteristic of the solvent. In water, the basic species is the anion characteristic of the solvent, OH-. By extending the Arrhenius definitions of acid and base to liquid ammonia, it becomes apparent from Eq. (10.3) that the acidic species is NH4+ and the basic species is Nl I,. It is apparent that any substance that leads to an increase in the concentration of NH4+ is an acid in liquid ammonia. A substance that leads to an increase in concentration of NH2- is a base in liquid ammonia. For other solvents, autoionization (if it occurs) leads to different ions, but in each case presumed ionization leads to a cation and an anion. Generalization of the nature of the acidic and basic species leads to the idea that in a solvent, the cation characteristic of the solvent is the acidic species and the anion characteristic of the solvent is the basic species. This is known as the solvent concept. Neutralization can be considered as the reaction of the cation and anion from the solvent. For example, the cation and anion react to produce unionized solvent ... 

The limitations of the Arrhenius theory of acids and bases are overcome by a more general theory, called the Bronsted-Lowry theory. This theory was proposed independently, in 1923, by Johannes Br0nsted, a Danish chemist, and Thomas Lowry, an English chemist. It recognizes an acid-base reaction as a chemical equilibrium, having both a forward reaction and a reverse reaction that involve the transfer of a proton. The Bronsted-Lowry theory defines acids and bases as follows ... 

Thus far we ve been using the Arrhenius theory of acids and bases (Section 4.5). According to Arrhenius, acids are substances that dissociate in water to produce hydrogen ions (H + ), and bases are substances that dissociate in water to yield hydroxide ions (OH-). Thus, HC1 and H2SO4 are acids, and NaOH and Ba(OH)o are bases. 

According to the Arrhenius theory of acids and bases, a basic solution has more hydroxide ions than hydrogen ions. 

Arrhenius theory of acids and bases the theory stating that an acid is a substance that produces hydrogen ions in water and a base is a substance that produces hydroxide ions in water (10.1)... 

This tendency of water molecules to break apart other molecules is part of the first definition of acids and bases, known as the Arrhenius theory of acids and hases and named after (surprise ) a chemist named Svante Arrhenius. According to Arrhenius, an acid is a substance that increases the concentration of H-i- ions in an aqueous (water) solution. So, hydrogen chloride (HCl) dissolved in water is an acid because the water breaks this molecule up into ions and CT ions. Actually, this statement is a bit of a lie because ions (which are simply protons—take away an electron from hydrogen, which is com-... 

Arrhenius theory of acids and bases. A theory of acids and bases in which an acid is defined as any substance that contributes protons or, more accurately, hydronium ions, in solution and a base is defined as any substance that contributes a hydroxide ion (OH ) in solution. 

In 1884, Svante Arrhenius (1859-1927) presented his theory of electrolytic dissociation, which resulted in the Arrhenius theory of acid-base reactions. In his view. 

The Arrhenius theory of acid-base behavior satisfactorily explained reactions of protonic acids with metal hydroxides (hydroxy bases). It was a significant contribution to chemical thought and theory in the latter part of the nineteenth century. The Arrhenius model of acids and bases, although limited in scope, led to the development of more general theories of acid-base behavior. They will be considered in later sections. 

These definitions are sufficiently broad that any hydrogen-containing molecule or ion capable of releasing a proton, H+, is an acid, whereas any molecule or ion that can accept a proton is a base. (In the Arrhenius theory of acids and bases, only substances that contain the OH group would be called bases.)... 

According to the modern version of the Arrhenius theory of acids and bases, a base is a substance that produces hydroxide ions, OH , when it is added to water. A solution that has a significant concentration of hydroxide ions is called a basic solution. Sodium hydroxide, NaOH, is the most common laboratory base. It is designated a strong base because for every NaOH unit dissolved, one hydroxide ion is formed in solution. 

A (a) Give an example of a substance that is an acid and one that is a base, according to the Arrhenius theory of acids and bases, (b) Give an example of a Bronsted-Lowry acid that is not an Arrhenius acid, (c) Give an example of a Brunsted-Lowry base that is not an Arrhenius base. 

In 1884, Svante Arrhenius observed that all substances called acids contain hydrogen ions, H. Bases, on the other hand, always contained hydroxide ions, OH . An acid was thus identified as a substance whose water solution contains more hydrogen ions than hydroxide ions, and a base is a substance whose water solution contains more hydroxide ions than hydrogen ions. According to the Arrhenius theory of acids and bases, the properties of an acid are the properties of the hydrogen ion, and the properties of a base are the properties of the hydroxide ion. 

Section 17.1 The Arrhenius Theory of Acids and Bases (Optional)... 

Equations (5.9) and (5.10) are based on the Arrhenius theory of acids and bases, and these equations might lead you to think that acids simply fall apart into H ions and the accompanying anions when they are dissolved in water. However, plenty of experimental evidence proves that this is not the case. In 1923, Johannes Bronsted in Denmark and Thomas Lowry in Great Britain independently proposed that the key process responsible for the properties of acids (and bases) is the transfer of an H ion (a proton) from one substance to another. For example, when acids dissolve in water, H ions are transferred from acid molecules to water molecules, as shown below for HCl and CH3C(X)H. 

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