Autoionization of liquid

Seemingly, another possible autoionization of liquid N204 could involve splitting the molecule in a different way to produce N02+ and N02-,... 

Explain the role of hydrogen bonding in the autoionization of liquid HF. 

A. Label each substance in the equation for the autoionization of liquid ammonia as Brpnsted acid or base ... 

The autoionization of liquid ammonia is given by Equation (14.5). Thus, any species that is capable of increasing the concentration of ammonium ion in liquid ammonia is considered to be an acid and any species that generates NH2 is a base ... 

The conductivity of liquid ammonia is sufficiently high to indicate a very slight degree of autoionization. In order for ions to be produced, something must be transferred from one molecule to another, and in solvents such as water or ammonia it is proton transfer that occurs. Accordingly, the ionization of liquid ammonia can be shown as... 

However, in liquid N204 reactions do not occur as if N02+ and N02 were present, and there is no evidence to indicate that they are. In most cases, autoionization of the solvent if it occurs is by transfer... 

The conductivity of liquid HF indicates slight autoionization that can be represented as... 

A solvent that resembles water in many ways is liquid hydrogen fluoride. The molecule is polar, there is some autoionization, and it is a fairly good solvent for numerous ionic solids. Although the boiling point of liquid HF is rather low (19.5 °C), it has a liquid range that is comparable to that of water, partially as a result of extensive hydrogen bonding. One of the problems associated with the use of liquid... 

A slight degree of autoionization in liquid IF5 is indicated by the conductivity. 

The low conductivity of liquid S02 has been interpreted as arising from ions produced by autoionization ... 

Presuming the solvent concept to apply in the case of liquid sulfur dioxide, SOCI2 would be an acid that produces S02+. It may be that SOCI2 undergoes some slight autoionization that can be represented as... 

You travel to a distant, cold planet where the ammonia flows like water. In fact, the inhabitants of this planet use ammonia (an abundant liquid on their planet) much as earthlings use water. Ammonia is also similar to water in that it is amphoteric and undergoes autoionization. The K value for the autoionization of ammonia is 1.8 X 10 12 at the standard temperature of the planet. What is the pH of ammonia at this temperature ... 

El 7.15 (a) SbFf The acid/base properties of liquid BrFj result from the following autoionization reaction ... 

Another acid-base theory that is useful for solvents other than water was postulated by American chemist Fdward Franklin in 1905. It makes use of the autoionization of solvents, and defines an acid as a solute that produces the positively charged species of the solvent and a base as a solute that produces the negatively charged species of the solvent. In the case of the autoionization of water (equation 18) HjO is the acid and OH is the base. For the nonaqueous solvent, liquid ammonia, the autoionization gives... 

Following Platzman (1967), Magee and Mozumder (1973) estimate the total ionization yield in water vapor as 3.48. The yield of superexcited states that do not autoionize in the gas phase is 0.92. Assuming that all of these did autoion-ize in the liquid, we would get 4.4 as the total ionization yield. This figure is within the experimental limits of eh yield at 100 ps, but it is less than the total experimental ionization yield by about 1. The assumption of lower ionization potential in the liquid does not remove this difficulty, as the total yield of excited states in the gas phase below the ionization limit is only 0.54. 

According to the Arrhenius theory of acids and bases, the acidic species in water is the solvated proton (which we write as H30+). This shows that the acidic species is the cation characteristic of the solvent. In water, the basic species is the anion characteristic of the solvent, OH-. By extending the Arrhenius definitions of acid and base to liquid ammonia, it becomes apparent from Eq. (10.3) that the acidic species is NH4+ and the basic species is Nl I,. It is apparent that any substance that leads to an increase in the concentration of NH4+ is an acid in liquid ammonia. A substance that leads to an increase in concentration of NH2- is a base in liquid ammonia. For other solvents, autoionization (if it occurs) leads to different ions, but in each case presumed ionization leads to a cation and an anion. Generalization of the nature of the acidic and basic species leads to the idea that in a solvent, the cation characteristic of the solvent is the acidic species and the anion characteristic of the solvent is the basic species. This is known as the solvent concept. Neutralization can be considered as the reaction of the cation and anion from the solvent. For example, the cation and anion react to produce unionized solvent ... 

This reaction represents a neutralization reaction in liquid sulfur dioxide. It makes no difference that the solvent does not ionize or that SOCl2 is a covalent molecule. The utility of the solvent concept is not that it correctly predicts that solvents undergo some autoionization. The value of the solvent concept is that it allows us to correctly predict how reactions would take place if the solvent ionized. Note that in this case SOCl2 does not ionize, but if it did it would produce S02+ (the acidic species characteristic of the solvent) and Cl-. 

The concepts just illustrated can be extended to other nonaqueous solvents. For example, in liquid N204 if autoionization occurred it would produce NO+ and N03 . In this solvent, a compound that furnishes N03- would be a base, and a compound that would (formally rather than actually) produce NO+ would be an acid. Therefore, the reaction of KN03 with NOC1 (actually linked as ONC1) is a neutralization in liquid N204. 

One of the chief difficulties with the solvent system concept is that in the absence of data, one is tempted to push it further than can be justified. For example, the reaction of thionyl halides with sulfites in liquid sulfor dioxide might be supposed to occur as follows, assuming that autoionization occurs ... 

A point of this reaction is the release of H+ ions—the Bronsted-Lowry approach considers this the appearance of a proton from the acid. A Bronsted-Lowry acid is a proton donor. Note that the hydrogen ion is a proton, hydrogen s nucleus without the electron found in the atom. Then, a Bronsted-Lowry acid must contain a hydrogen. Of course, if the solvent were not to be water, this statement may not work because the cation released could be other than the hydrogen ion, but there might be other ions performing the same service (liquid ammonia autoionizes, Problem 17.3). 

These equations show that FeCLT can form by coordination of the solvent rather than by postulating solvent autoionization according to the solvent concept. In the series of reactions represented by Eq. (5.69), nucleophilic substitution occurs in which a solvent molecule replaces a chloride ion that subsequently interacts with FeCl3. Undoubtedly, a similar situation exists for other reactions in which autoionization appears to occur. Autoionization probably occurs only in solvents in which a proton that is strongly solvated is transferred (H20, HF, NH3, etc.). Although the solvent concept is useful in a formal way, it is unlikely that autoionization occurs for a solvent such as liquid SO2. However, many reactions take place to give the products that would be predicted if autoionization had occurred. We will now describe the chemistry of three of the most extensively studied nonaqueous solvents. 

As a result, if autoionization does occur, the extent must be slight. In fact, there is no experimental basis for assuming that any autoionization occurs. Radioactive sulfur in SOCl2 is not exchanged with the sulfur in liquid S02. If the two solvents undergo ionization to produce S02+, it would be expected that exchange of sulfur would occur. 

Selenyl chloride is the most important of the three selenium compounds having the formula SeOX2, and it has been used as a nonaqueous solvent. The liquids have substantial conductivity so it is presumed that some autoionization occurs in both SeOCl2 and SOCl2 ... 

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