Water Brpnsted-Lowry theory

According to Brpnsted-Lowry theory, a water molecule can accept a proton, thereby becoming a hydronium ion. In this case, water is acting as a base (proton acceptor). 

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 ... 

In this ionization reaction, water serves not only as a solvent but also as a base according to the Brpnsted-Lowry theory. 

Reaction (4.9) is not equilibrated. This fact must not be interpreted as being a consequence of a shortcoming in the Brpnsted-Lowry theory. Actually, and simply, the chloride ion is too weak a base in water. Additionally, it is recognized as being a base in some other solvents. 

The Brpnsted-Lowry theory states that acid-base reactions are a competition for a proton. For exeunple, take a look at the reaction of ammonia with water ... 

Acids and bases are an important class of compounds dissolved in aqueous solution and often found in common household products as well as in many drugs. When you eat a grapefruit or a lemon, it tastes sour due to the presence of acids. Coffee and tonic water, on the other hand, taste bitter, due to the presence of bases. The definition of an acid is based on the Brpnsted-Lowry theory, which specifies that acids produce protons (H+) in aqueous solution, that is, they are proton donors. 

At the microscopic level, the Arrhenius theory defines acids as substances which, when dissolved in water, yield the hydronium ion (H30+) or H+(aq). Bases are defined as substances which, when dissolved in water, yield the hydroxide ion (OH). Acids and bases may be strong (as in strong electrolytes), dissociating completely in water, or weak (as in weak electrolytes), partially dissociating in water. (We will see the more useful Brpnsted-Lowry definitions of acids and bases in Chapter 15.) Strong acids include ... 

Arts. The Arrhenius model focuses on the acid or base molecule only, in that an acid is defined as a molecule which dissociates in water to produce protons, and a base is defined as a molecule which dissociates in water to produce hydroxyl ions. In the Brpnsted-Lowry model, the solvent assumes a central role. This theory proposes that an acid is a compound which can donate protons to a base, and consequently, a base is a compound which can accept the acid s donated proton. Therefore, an acid cannot behave as an acid in the absence of a base. Water assumes a central role in these processes, since in the presence of an acid, it acts as a base, accepting the acid s proton. Furthermore, in the presence of a base, it can donate a proton, and act as an acid. 

Hydrogen bonding. Interaction between molecules or portions of a molecule resulting from the Lewis acid or base properties of the molecular units. Most commonly applied to water or hydroxyl containing systems (e.g., alcohols) in the sense of Brpnsted-Lowry acid-base theory, but also found in molecules having hydrogen bound to nitrogen (amines and amides). 

See pH. When dealing with chemical reactions in solvents other than water, it is sometimes convenient to define an acid as a substance that ionizes to give the positive ion of the solvent. The common definitions of acid have been extended as more detailed studies of chemical reactions have been made. The Lowry-Brpnsted definition of an acid as a substance that can give up a proton is more useful in connection with an understanding of bases (see base). Perhaps the most significant contribution to the theory of acids was the electron-pair concept introduced by G. N. Lewis around 1915. 

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