Strong acids, hydration

Water was born to conduct protons (see Special Issue Is life possible without water [67]). The conductance of distilled water is miserable due to a negligible concentration of free protons (10 mol/liter), but the proton mobility in water is approximately five times higher than the mobility of an alkali cation (e.g. Na" ), an object of similar size as the hydronium (HaO ) ion [68]. So, donated protons can run fast through the aqueous phase. Excess protons result from dissociation of acidic molecules or molecular groups, e.g. in solutions of strong acids, hydrated polymer-electrolytes, or proteins. In acidic solutions both the protons and counter-anions are mobile. In polymer-electrolyte membranes and in proteins only protons are mobile in the connected aqueous phase while the counter anions are mostly a part of an immobile skeleton. 

Excess protons in aqueous electrolyte result from the dissociation of acid molecules or molecular groups in solutions of strong acids, hydrated polymer electrolytes, or proteins. In acidic solutions, both protons and counter-anions are mobile. In PEMs, only protons are mobile while anions are immobilized at the macromolec-ular matrix or skeleton of the pore network. 

Consequently they cannot be prepared by the addition of sulphide ions to a solution of the metal salt, the hydrated metal ions being so strongly acidic that the following reaction occurs, for example... 

Dead-burned magnesia, characterized by large crystaUite size and very low chemical reactivity, is resistant to the basic slags employed in the metals refining industry. It reacts very slowly with strong acids, and does not readily hydrate or react with carbon dioxide unless finely pulverized. 

Another synthesis of Lyral (51) consists of the reaction of myrcene with acrolein to give the myrac aldehyde [37677-14-8] (52). The aldehyde group, which is sensitive to acid hydration conditions with strong acids, has to be protected by formation of the morpholine enamine. The enamine is then hydrolyzed on workup after the acid-catalyzed hydration to produce Lyral (93—95). 

The chemistry of vanadium compounds is related to the oxidation state of the vanadium. Thus, V20 is acidic and weaMy basic, VO2 is basic and weaMy acidic, and V2O2 and VO are basic. Vanadium in an aqueous solution of vanadate salt occurs as the anion, eg, (VO ) or (V O ) , but in strongly acid solution, the cation (V02) prevails. Vanadium(IV) forms both oxyanions ((V O ) and oxycations (VCompounds of vanadium(III) and (II) in solution contain the hydrated ions [V(H20)g] and [V(H20)g], respectively. 

Strong acids also catalyze the addition of alcohols to alkenes to give ethers, and the mechanistic studies which have been done indicate that the reaction closely parallels the hydration process. ... 

Bell has calculated Hq values with fair accuracy by assuming that the increase in acidity in strongly acid solutions is due to hydration of hydrogen ions and that the hydration number is 4. The addition of neutral salts to acid solutions produces a marked increase in acidity, and this too is probably a hydration effect in the main. Critchfield and Johnson have made use of this salt effect to titrate very weak bases in concentrated aqueous salt solutions. The addition of DMSO to aqueous solutions of strong bases increases the alkalinity of the solutions. 

The effect of metalloids on the corrosion resistance of alloys also varies with the stability of polyoxyanions contained in their films. Phosphorus and carbon contained in iron-chromium-melalloid alloys do not produce passive films of phosphate and carbonate in strong acids, and so do not interfere with the formation of the passive hydrated chromium oxyhydroxide... 

Water adds to alkenes to yield alcohols, a process called hydration. The reaction takes place on treatment of the alkene with water and a strong acid catalyst (HA) by a mechanism similar to that of HX addition. Thus, protonation of an alkene double bond yields a carbocation intermediate, which reacts with water to yield a protonated alcohol product (ROH2+). Loss of H+ from this protonated alcohol gives the neutral alcohol and regenerates the acid catalyst (Figure 7.2). 

Acid-catalyzed alkene hydration is particularly suited to large-scale industrial procedures, and approximately 300,000 tons of ethanol are manufactured each year in the United States by hydration of ethylene. The reaction is of little value in the typical laboratory, however, because it requires high temperatures— 250 °C in the case of ethylene—and strongly acidic conditions. 

Chromic hydroxide, Cr(OH)3, is a compound with low solubility in water. It is usually hydrated and does not have the definite composition represented by the formula. It is quite soluble either in strong acid or strong base. 

The typical strong acid of the water system is the hydrated proton H30+, and the role of the conjugate base is minor if it is a sufficiently weak base, e.g. Cl-, Br-, and C104. The conjugate bases have strengths that vary inversely as the strengths of the respective acids. It can easily be shown that the basic ionisation constant of the conjugate base KR canj is equal to Kw/KA conj, where Kw is the ionic product of water. 

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