Brpnsted acids and bases

In Chapter 4 we defined a Brpnsted acid as a substance capable of donating a proton, and a Brpnsted base as a substance that can accept a proton. These definitions are generally suitable for a discussion of the properties and reactions of acids and bases. 

An extension of the Brpnsted definition of acids and bases is the concept of the conjugate acid-base pair, which can be defined as an acid and its conjugate base or a base and its conjugate acid. The conjugate base of a Brpnsted acid is the species that remains when one proton has been removed from the acid. Conversely, a conjugate acid results from the addition of a proton to a Brpnsted base. 

Every Brpnsted acid has a conjugate base, and every Brpnsted base has a conjugate acid. For example, the chloride ion (CF) is the conjugate base formed from the acid HCl, and (hydronium ion) is the conjugate acid of the base H2O. 

The proton is always associated with water molecules in aqueous solution. The H3O ion is the simplest formula of a hydrated proton. 

The subscripts 1 and 2 designate the two conjugate acid-base pairs. Thus, the acetate ion (CH3COO ) is the conjugate base of CH3COOH. Both the ionization of HCl (see Section 4.3) and the ionization of CH3COOH are examples of Brpnsted acid-base reactions. 

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Periodic Table Correlations. When comparing Brpnsted acids and bases that differ in the position of an element in the periodic table ... 

Of course, in a generalized way, the proton H+ is also a Lewis acid and the Brpnsted acids and bases also fall into the Lewis categories. 

The ability of compounds to function as Brpnsted acids or bases is not limited to aqueous solutions, and the reaction of gaseous HC1 and NH3 has already been described. A great many compounds also behave as Brpnsted acids and bases in the molten state. For example, molten NFLtCl and pyridinium chloride (also known as pyridine hydrochloride, C5H5NH+CF) readily undergo reactions that are typical of acids. In some of the early studies on this type of chemical behavior, a large number of reactions of molten NFI4CI with metals and metal compounds were carried out. Typical reactions are illustrated in the following equations ... 

Predict the relative acid/base strengths of Brpnsted acids and bases. 

As in general chemistry, acid-base reactions are of fundamental importance in organic chemistry. Organic acids and bases, as well as inorganic acids and bases, occur frequently in reactions, and large numbers of reactions are catalyzed by Brpnsted acids and bases and Lewis acids and bases. 

Aqueous solutions of most salts test acidic or basic. We can explain this in terms of the strengths of Brpnsted acids and bases. For example, an aqueous solution of sodium acetate tests basic to litmus paper. The solutes are the feeble acid Na and the weak base C2H3O2. Because the base present is a stronger base (not a strong base) than the acid present is an acid, the solution tests basic ... 

However, for those that are Brpnsted acids or bases, values increase dramatically as the pH is reduced below the value(s) for the compound (Haderlein and Schwarzenbach, 1993 Broholm et al, 2001). (The pK of a Brpnsted acid/base pair is the negative log of the equilibrium constant for their interconversion through the gain or loss of a proton. As such, the pK, also represents the pH value below which the concentration of the acid exceeds that of the base, and above which the base dominates.) Schellenberg et al. (1984) introduced equations that may be used to quantify the effects of pH variations on Kp for Brpnsted acids and bases. 

Maybe one of the most important questions to be answered relates to the degree of dissociation of Brpnsted acids and bases in ionic liquids. Acids are ubiquitously used as catalysts to initiate reactions such as the Fischer-type esterification or ether formation from alcohols. 

Weak-electron sharing bonding In magnitude, this is of the same value as the hydrogen bond. It is also the Lewis acid-Lewis base bond (comparable to Brpnsted acids and bases). Such forces might contribute appreciably to cohesiveness at interfaces a typical example is the weak association of iodine (I2) with benzene or any polyaromatic compound. The interaction is the donation of the electrons of I2 to the electron-deficient aromatic molecules (jr-electrons). 

The same equation has also been used to quantify the amount of specifically adsorbed cations. For both Lewis and Brpnsted acids and bases this adsorption isotherm relates to the Hammett function (Equations 8.80, 8.109, and 8.110). 

The decyanation reaction is also observed employing Brpnsted acids and bases, although the harsh reaction conditions required (very high temperatures and long reaction times) limit the applicability of this method. 

Identify the Brpnsted acid and base in each case. 

Both the amide ion (NH2 ) and the nitride ion (N ) are stronger bases than the hydroxide ion and hence do not exist in aqueous solutions, (a) Write equations showing the reactions of these ions with water, and identify the Brpnsted acid and base in each case, (b) Which of the two is the stronger base ... 

The topmost layer in Fig. 5.18 is made up of the neutral coordinatively saturated cations in the (001) surface for the layered V2O5 bulk material. In contrast, the (110) surface is formed by the cleavage of covalent V-0 bonds at the surface, thus resulting in coordinatively unsaturated V and 0 atoms at its side faces as shown in Fig. 5.18. The less reactive (001) surface is thought to be responsible for the selective oxidation of hydrocarbons such as toluene, whereas the reactive (110) surface predominantly results in total oxidation. This surface is also easily hydroxylated and, hence, contains both Brpnsted acid and base sites. 

Identify each Brpnsted acid and base in the following equations. Note that the reactions are assumed to be reversible. 

Write equations to illustrate the acid-base reaction when each of the following pairs of Brpnsted acids and bases are... 

Johannes Nicolaus Brdnsted (1879-1947). Danish chemist. In addition to his theory of acids and bases, Br0nsted worked on thermodynamics and the separation of mercury into its isotopes. In some books. Brpnsted acids and bases are called Bronsted-Lowry acids and bases. Thomas Martin Lowry (1874—1936). English chemist. Brpnsted and Lowry developed essentially the same acid-base theory independently in 1923. 

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