Acid-base reactions dissociation

Acid-base reactions occur when an acid donates a proton to a base. The equilibrium position of an acid-base reaction is described using either the dissociation constant for the acid, fQ, or the dissociation constant for the base, K, . The product of and Kb for an acid and its conjugate base is K (water s dissociation constant). 

In addition to simple dissolution, ionic dissociation and solvolysis, two further classes of reaction are of pre-eminent importance in aqueous solution chemistry, namely acid-base reactions (p. 48) and oxidation-reduction reactions. In water, the oxygen atom is in its lowest oxidation state (—2). Standard reduction potentials (p. 435) of oxygen in acid and alkaline solution are listed in Table 14.10- and shown diagramatically in the scheme opposite. It is important to remember that if or OH appear in the electrode half-reaction, then the electrode potential will change markedly with the pH. Thus for the first reaction in Table 14.10 O2 -I-4H+ -I- 4e 2H2O, although E° = 1.229 V,... 

Now the dissociation of acetic acid can be regarded as an acid-base reaction. The acid CHjCOOH transfers a proton to the base H20 forming the acid H30+ and the base CH3COO-. The reaction (54) now takes the form... 

Using Environmental Examples to Teach About Acids. Acid-base reactions are usually presented to secondary students as examples of aqueous equilibrium (2). In their study of acids and bases, students are expected to master the characteristic properties and reactions. They are taught to test the acidity of solutions, identify familiar acids and label them as strong or weak. The ionic dissociation of water, the pH scale and some common reactions of acids are also included in high school chemistry. All of these topics may be illustrated with examples related to acid deposition (5). A lesson plan is presented in Table I. 

In solutions neither H+ nor e can exist in a free state they will be donated only if they are accepted within the solution, e.g., by another acceptor, which may be the solvent and thus cause solvation here the mere solvation of electrons is an exceptional case, but may occur, e.g., in liquid ammonia, where according to Kraus82 the strongly reducing alkali metals dissolve while dissociating into cations M+ and solvated electrons e, which, however, are soon converted into NH2" and H2 gas. Further, from the analogy with acid-base reactions and the definition of... 

Acid-base reactions of buffers act either to add or to remove hydrogen ions to or from the solution so as to maintain a nearly constant equilibrium concentration of H+. For example, carbon dioxide acts as a buffer when it dissolves in water to form carbonic acid, which dissociates to carbonate and bicarbonate ions ... 

The Arrhenius theory explains acid-base reactions as a combination of H (aq) and OH (aq). It provides insight into the heat of neutralization for the reaction between a strong acid and a strong base. (Strong acids and bases dissociate completely into ions in solution.) For example, consider the following reaction. 

The acidic or basic property of an aqueous solution of a salt results from reactions between water and the dissociated ions of the salt. Some ions do not react with water. They are neutral in solution. Ions that do react with water produce a solution with an excess of HsO iaq) or OH (aq). The extent of the reaction determines the pH of the solution. As you will see, the reaction between an ion and water is really just another acid-base reaction. 

Proton transfer is one of the prominent representatives of an ion-molecule reaction in the gas phase. It is employed for the determination of GBs and PAs (Chap. 2.11.2) by either method the kinetic method makes use of the dissociation of proton-bound heterodimers, and the thermokinetic method determines the equilibrium constant of the acid-base reaction of gaseous ions. In general, proton transfer plays a crucial role in the formation of protonated molecules, e.g., in positive-ion chemical ionization mass spectrometry (Chap. 7). 

In contrast to redox reactions, only proton transfer takes place in acid-base reactions (see also p.30). When an acid dissociates (1), water serves as a proton acceptor (i. e., as a base). Conversely, water has the function of an acid in the protonation of a carboxylate anion (2). 

In order to understand why the activation energies differ between the two pathways, Mui et al. examined the transition state geometries [279]. They found that as electron density is donated from the amine lone pair to the down silicon atom upon adsorption into the precursor state, the up Si atom in the dimer becomes electron rich. At this stage, the dative bonded precursor can be described as a quaternary ammonium ion. The N—H dissociation pathway can thus be interpreted as the transfer of a proton from the ammonium ion to the electron-rich up Si atom through a Lewis acid-base reaction. In the transition state for this proton transfer, the N—H and Si—H... 

This book was written to provide readers with some knowledge of electrochemistry in non-aqueous solutions, from its fundamentals to the latest developments, including the current situation concerning hazardous solvents. The book is divided into two parts. Part I (Chapters 1 to 4) contains a discussion of solvent properties and then deals with solvent effects on chemical processes such as ion solvation, ion complexation, electrolyte dissociation, acid-base reactions and redox reactions. Such solvent effects are of fundamental importance in understanding chem-... 

In order that the acid HA dissociates almost completely into H+ and A-, i.e. in order to get a large Ka value, it is essential that both the ionization and the dissociation processes occur easily. This means that both K, and KD should be large enough, as is often the case in amphiprotic solvents of high pennittivities. In the following sections, we discuss the characteristics of acid-base reactions in each of the four classes of solvents. 

The characteristics of acid-base reactions in dipolar aprotic solvents, compared to those in dipolar amphiprotic solvents, are the easy occurrence of homo- and heteroconjugation reactions [2, 3, 5]. However, before discussing the homo- and heteroconjugations, we first discuss the solvent effects on the acid dissociation constants in dipolar aprotic solvents. 

Reactions other than Lewis acid-base associations/dissociations are frequently observed wit donor molecules, leading notably to solvolysis, oxygen or sulfur abstraction, insertion reaction and carbon-carbon coupling reactions. The tendency to form metal-element multiple bonds i remarkable in this respect the activation of dinitrogen by tantalum or niobium is unique. Th formation and chemistry of constrained reactive metallacycles open another promisin fast-developing area, on the frontier with organometallic chemistry. 

Any ionic solid, such as ammonium chloride, is called a salt. In a formal sense, a salt can be thought of as the product of an acid-base reaction. When an acid and base react, they are said to neutralize each other. Most salts containing cations and anions with a single positive and negative charge are strong electrolytes—they dissociate nearly completely into ions in dilute aqueous solution. Thus, ammonium chloride gives NH and Cl- in water ... 

What then is the difference between an acid and an electrophile, or between a base and nucleophile No great difference until we try to use the terms in a quantitative sense. For example, if we refer to acid strength, or acidity, this means the position of equilibrium in an acid-base reaction. The equilibrium constant Ka for the dissociation of an acid FIA, or the pKa, is a quantitative measure of acid strength. The larger the value of Ka or the smaller the pKa, the stronger the acid. 

To see what s going on in an acid-base reaction, keep your eye on the proton. For example, when a Bronsted-Lowry acid HA is placed in water, it reacts reversibly with water in an acid-dissociation equilibrium. The acid transfers a proton to the solvent, which acts as a base (a proton acceptor). The products are the hydronium ion, H30+ (the conjugate acid of H20), and A- (the conjugate base of HA) ... 

Related ammonium salts derived from amines, such as [CH3NH3]C1, [(CH3)2NH2]C1, and [(CH3)3NH]C1, also give acidic solutions because they too have cations with at least one dissociable proton. The pH of a solution that contains an acidic cation can be calculated by the standard procedure outlined in Figure 15.7. For a 0.10 M NH4C1 solution, the pH is 5.12. Although the reaction of a cation or anion of a salt with water to produce H30+ or OH - ions is sometimes called a salt hydrolysis reaction, there is no fundamental difference between a salt hydrolysis reaction and any other Bronsted-Lowry acid-base reaction. 

According to the Arrhenius theory, acids (HA) are substances that dissociate in water to produce H + (aq). Bases (MOH) are substances that dissociate to yield OH aq). The more general Bransted-Lowry theory defines an acid as a proton donor, a base as a proton acceptor, and an acid-base reaction as a proton-transfer reaction. Examples of Bronsted-Lowry acids are HC1, NH4+, and HSO4- examples of Bronsted-Lowry bases are OH-, F-, and NH3. 

Sometimes the acid-base reaction involved is more complex than that indicated in scheme (19). The two most frequently observed complications are participation of proton-donors other than hydroxonium ion and dissociation of two or more protons. Participation of various proton-donors is demonstrated by the dependence of the height of the kinetically controlled wave on the nature and concentration of the buffer with the usual type of buffers, a pH-dependence of wave f in the shape of a deformed dissociation curve is obtained. For polybasic acids several po-larographic dissociation curves are observed at various pK -values under certain conditions the slopes of these curves may differ. 

The proton produced by the dissociation of hydrochloric acid protonates the alcohol molecule in an acid-base reaction. 

There are some cases where a reaction, that is, the formation or dissolution of a chemical bond, is involved along with ion exchange phenomena (Helfferich, 1983). Examples of this are acid-base neutralization, dissociation of weak electrolytes in solution or weak ionogenic groups in ion exchangers, complex formation, or combinations of these (Table 5.2). With some of these, very low apparent D in ion exchangers have been noted. 

Chlorine gas is added to the water in some large commercial swimming pools to kill bacteria. However, in most home swimming pools, either solid calcium hypochlorite (Ca(OCl)2) or an aqueous solution of sodium hypochlorite (NaOCl) is used to treat the water. Both compounds dissociate in water to form the weak acid hypochlorous acid (HOC1). Hypochlorous acid is a highly effective bactericide. By contrast, the hypochlorite ion (OC1-) is not a very effective bactericide. Use the information above to answer the following questions about the acid-base reactions that take place in swimming pools. 

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