Hydrogen ion in aqueous solutions

The values of the free energy of formation of the negative halogenide ions (plus hydrogen ion) in aqueous solution might be expected to depend in a simple way on the electronegativity of the atoms. It is found (Fig. XI-1) that there is a linear relation, represented by the equation... 

The word protic refers to chemistry involving transfer of H+ from one molecule to another. The species H+ is also called a proton because it is what remains when a hydrogen atom loses its electron. Hydronium ion, H30+, is a combination of H+ with H20. Although H,0 is a more accurate representation than H+ for the hydrogen ion in aqueous solution, we will use H30+ and H+ interchangeably in this book. 

VI. Catalysis by Species other than Hydrogen Ions in Aqueous Solution. . 312... 

Equations (38) to (40) represent the formation of the transition state for the three most commonly considered mechanisms of acid catalysis for hydrogen ions in aqueous solution. They are designated A-l, A-2 and A-S 2 mechanisms, and the appropriate equilibrium constants for the formation of the respective transition states are expressed by equations (41) to (43). Equations for other mechanisms—the existence of which we certainly do not wish to exclude by implication—can be developed in an analogous fashion. 

The wet (hydrated) hydrogen ion in aqueous solution is often represented as and will be so written in this text. It should be... 

HsO+) hydronium. the HsO+ ion, formed by capture of a hydrogen ion by a water molecule. A strong covalent bond is formed between the hydrogen ion and water oxygen all hydrogen ions in aqueous solution are bound inside hydronium ions. 

The first person to recognize the essential nature of acids and bases was Svante Arrhenius. Based on his experiments with electrolytes, Arrhenius postulated that acids produce hydrogen ions in aqueous solution, and bases produce hydroxide ions. At the time of its discovery the Arrhenius concept of acids and bases was a major step forward in quantifying acid—base chemistry, but this concept is limited because it applies only to aqueous solutions and allows for only one kind of base—the hydroxide ion. A more general definition of acids and bases was suggested independently by the Danish chemist Johannes N. Bronsted (1879-1947) and the English chemist Thomas M. Lowry (1874-1936) in 1923. In terms of the Bronsted—Lowry definition, an acid is a proton (H+) donor, and a base is a proton acceptor. For example, when gaseous HCl dissolves in water, each HCl molecule donates a proton to a water molecule, and so HCl qualifies as a Bronsted-Lowry acid. The molecule that accepts the proton—water in this case—is a Bronsted-Lowry base. 

Aromatic hydrocarbon one of a special class of cyclic unsaturated hydrocarbons, the simplest of which is benzene. (22.3) Arrhenius concept a concept postulating that acids produce hydrogen ions in aqueous solution, whereas bases produce hydroxide ions. (7.1)... 

The hydrogen ion in aqueous solutions is almost certainly associated with more than one water molecule (for the structure of water seep. 232). H3O+ exists in some ionic lattices, however, for instance in HgO+ClO - which is isomorphous with NH4+C104. ... 

Compounds such as hydrogen chloride that produce hydrogen ions in aqueous solution are acids. In fact, an aqueous solution of hydrogen chloride is often referred to as hydrochloric acid. You ll learn more about acids in Chapter 19. 

The hydronium ion is a hydrated hydrogen ion, which means that a water molecule is attached to a hydrogen ion by a covalent bond. However, the symbols H+ and H3O+ can be used interchangeably in chemical equations to represent a hydrogen ion in aqueous solution. Thus, a simplified version of the equation for the self-ionization of water is... 

The Arrhenius model of acids and bases If pure water itself is neutral, how does an aqueous solution become acidic or basic The first person to answer this question was the Swedish chemist Svante Arrhenius, who in 1883 proposed what is now called the Arrhenius model of acids and bases. The Arrhenius model states that an acid is a substance that contains hydrogen and ionizes to produce hydrogen ions in aqueous solution. A base is a substance that contains a hydroxide group and dissociates to produce a hydroxide ion in aqueous solution. Some household acids and bases are shown in Figure 19-3. 

Arrhenius model (p. 597) A model of acids and bases states that an acid is a substance that contains hydrogen and ionizes to produce hydrogen ions in aqueous solution and a base is a substance that contains a hydroxide group and dissociates to produce a hydroxide ion in aqueous solution. 

As discussed in Chapter 15, a hydrogen ion in aqueous solution is closely held hy a water molecule and is better represented as a hydronium ion, HjO (aq). 

Aqueous solutions of most protonic acids (those containing acidic hydrogen atoms) exhibit certain properties, which are properties of hydrated hydrogen ions in aqueous solution. 

Substances which liberate hydrogen ions in aqueous solution are called acids. Bases, on the other hand, split off hydroxyl ions. The various acids and bases differ quantitatively in the... 

Conversely, if both constants of a dibasic acid are known, the concentration of hydrogen ions in aqueous solution can be calculated. Although it is difficult to solve an equation of the third degree, the correct value can be found by the method of trial and error. The labor involved can be materially reduced by the simple procedure described below. 

Acids are defined classically as substances which liberate hydrogen ions in aqueous solutions, while bases are substances which dissociate in water with the formation of hydroxyl ions. This formulation of the concept of acids and bases had developed chiefly on the basis of acidic and basic properties displayed in aqueous solutions. When an attempt was made to establish a more general theory of acids and bases, the old formulation appeared in many ways to be one-sided and incomplete. 

The H3O+ ion is called the hydronium ion. (it is a hydrogen ion attached to a water molecule, and is more real than a free hydrogen ion in aqueous solution, because the hydrogen ion has no electrons.) We will regard H+ and HsO to be two different ways to represent the same ion. Use whichever form the textbook uses. 

Acid a substance that produces hydrogen ions in aqueous solution a proton donor. 

As we will show later, this choice implies that the standard Gibbs energy of hydrogen ion in aqueous solution is zero. 

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