Acid-hase reactions

In acid-hase reactions, the heat of neutralization of aqueous acids and bases can he sufficient to cause spitting from containers when the concentrated reagents interact. This is also encountered when concentrated sulphuric acid is diluted (refer to Table 7.1) the acid should always be added cautiously to water and not vice versa. Eye and skin protection is obligatory when using such reagents. 

Write the Lewis structures of each reactant, identify the iTwis acid and the Lewis base, and then write the Lewis structure of the product (a complex) for rhe following I ewis acid-hase reactions ... 

Identify conjugate acid-hase pairs for selected acid-hase reactions, and compare their strengths. 

Use molecular models like those in Figures 4.7 and 4.8 to represent the following acid-hase reactions ... 

The cyclotetrasilene 2 not only undergoes acid-hase reactions (Scheme 1(b), 1(c)), but also redox reactions. So, reduction of 2 with supersilyl sodium R Na leads, as in Scheme 1(a), back to the tetrahedron 1. Over and above that, 2 reacts further with additional iodine at room temperature with elimination of supersilyl iodide R I and formation of an air- and moisture-stable yellow cyclotetrasilane 5 (Scheme 1(d) Fig.l). The expected intermediate R 4Si4lt could not be detected and possibly 5 is formed by other intermediates, hitherto not known. Heating a solution of 5 in benzene to I20°C in the presence of iodine leads, with elimination of another supersilyl iodide R I, quantitatively to the reasonably air-stable pale yellow cyclotetrasilane 6 (Scheme 1 (e) Fig. 2). 

Draw the anions formed from 16 and 18 and write out the acid-hase reaction of 18 with sodium bicarbonate. 

A bottie of hydrochioric acid (HCi, left) releases gaseous hydrogen chloride that reacts with gas phase ammonia (HH3,1 from an aqueous ammonia solution) in an acid-hase reaction. This produces the saH ammonium chloride (HH4CD as very small solid particles ( smoke ). 

Undo-stand the key events in precipitation and acid-hase reactions and use ionic equations to descrihe them distinguish between strong and weak acids and bases and... 

Describe how a Lewis acid-hase reaction involves formation of a new covalent bond, and identify Lewis acids and bases ( 18.8) (SP 18.14) (EPs 18.84-18.94)... 

Look closely at the acid-hase reaction in Figure 2.5, and note how it is shown. Dimethyl ether, the Lewis base, donates an electron pair to a vacant valence orbital of the boron atom in BF3, a Lewis acid. The direction of electron-pair flow from the base to the acid is shown using curved arrows, just as the direction of electron flow in going from one resonance structure to another was shown using curved arrows in Section 2.5. A curved arrow always means that a pair of electrons moves from the atom at the tail of the arrow to the atom at the head of the arrow. WeTl use this curved-arrow notation throughout the remainder of this text to indicate electron flow during reactions. 

Note that this reaction forms carbon dioxide gas as well as water, so it illustrates two of the driving forces that we have considered. Because this reaction involves that ends up in the product water, we classify it as an acid-hase reaction. 

J.6 Identify the salt that is produced from the acid-hase neutralization reaction between (a) potassium hydroxide and acetic acid, CH,COOH (b) ammonia and hydroiodic acid ... 

In the next chapter, you will extend your knowledge of equilibria involving aqueous ions. You will learn how to calculate the pH at an equivalence point, so you can select an appropriate indicator for any acid-hase titration. You will also learn why equilihrium is important to the solubility of compounds that are slightly soluble, and how to predict whether a precipitate will form as the result of a reaction between ions in solution. 

Figure 3 Proposed CODH mechanism. This mechanism proposes that the active state is Credl, consistent with recent electrochemical studies,which contains a hridghig hydroxide at the hinuclear NiFe center that serves as the nucleophile to attack a Ni-bound carbonyl forming a Ni-carboxylate. This OH, which is formed by acid-hase catalysis by indicated acid-base residues, is in the position of the bridging sulfide in the C. hydrogenoformans structure. The enzyme is proposed to remain in the Credl redox state until formation of CO2 when it becomes two-electrons reduced to the Cred2 state. Conversion of Credl to Cred2 occurs faster than electron transfer from Cred2 to the FeS clusters, which in turn reduce external electron acceptors. The electron transfer reactions are proposed to occur through a diamagnetic Cint state. ...

Bromolactonizatiott. Corey and Hase have observed high stereoselectivity in halolactonization of an acylic /3,y-unsaturated acid. Thus reaction of bromine with the thallium salt of frans-2-methyl-3-pentenoic acid (1) with Btj in CH2CI2 at —78° results in one halolactone (2) in about 90% yield, even though two additional asymmetric centers are introduced. The reaction was also conducted with the resolved acid. 

Recall that in an aqueous solution, a H+ ion exists as a H3O+ ion, so the net ionic equation for an acid-hase neutralization reaction is... 

Acid-base titration The stoichiometry of an acid-hase neutralization reaction is the same as that of any other reaction that occurs in solution. In the antacid reaction you just read about, one mole of magnesium hydroxide neutralizes two moles of hydrochloric acid. 

The acid-hase pair with the second highest concentration and a pK near the pH of seawater is horic acid (Table 4.1). The carbonate system and boric acid turn out to be by far the most important contributors to the acid-base chemistiy of seawater, but they contrast greatly in their reactivity in the ocean carbon is involved in all metabohc processes and varies in concentration from place to place, whereas borate is conservative and maintains a constant ratio to salinity. The equih-brium reaction and total boron, Bj, equations are ... 

The use of an ester solvent in acid catalysis is obviously inadvisable due to the possibility of an acid-catalysed reaction of reagent with the ester and/or acid-catalysed hydrolysis with adventitious water. The aldol reaction also normally precludes acid catalysis in ketone-hased solvents. 

For each of the following, write the complete acid-hase equilibrium and then write out the equation for K. For each reaction, draw a curved arrow for the acid-base pair to indicate the flow of electrons during the reaction ... 

Both E2 and El reactions are acid-base reactions. The E2 reaction requires a strong hase, but El reactions occur even with weak bases 2, 3, 4, 6, 7, 9, 21, 25, 26. 

The Arrhenius theory of acid-hase behavior satisfactorily explained reactions of protk 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. 

Hydroxide ion reacts with lactic acid as soon as it is produced. The endpoint of the reaction is detected with an acid—hase indicator. It required 115 s for a current of 15.6 mA to reach the endpoint. How many grams of lactic acid (a monoprotic acid) were present in the sample ... 

An acid-base reaction is often called a neutralization reaction. When just enough strong hase is added to react exactly with the strong acid in a solution, we say the acid has heen neutralized. One product of this reaction is always water. The steps in dealing with the stoichiometry of any neutralization reaction are the same as those we followed in the previous section. 

The acid formed when a base accepts a proton is called the conjugate acid of the base and the hase formed when an acid donates a proton is the conjugate base of the acid. Thus in the reaction... 

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