Amphoterism of hydrogen acids

Sulphuric acid, with the exception of the mentioned case, and in the mixtures with perchloric acid (no proton transfer), shows acidic function towards all other hydrogen acids. 

The well-known behavior of acidic function of absolute nitric acid towards absolute sulphuric acid is a circumstance widely used for the nitration of organic compounds. 

Trifluoroacetic acid reveals proton-acceptor function towards all strong mineral acids, but, at the same time, it acts as an acid towards acetic and monochloroacetic acids. 

In mixed solvents formed by two aliphatic carbonic acids, proton transfer does not take place and interaction is usually limited to a mixed associate formation, according to the equilibrium [9.2]. 

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Beryllium is readily attacked by most acids and, being amphoteric, is slowly attacked by caustic alkalis with the evolution of hydrogen. As might be anticipated, in view of the controlling influence of the surface film of beryllia on corrosion behaviour, concentrated nitric acid has little effect on beryllium , while the dilute acid results in slow attack. Hot acid is much more reactive. Nitric acid is in fact often used to pickle-off residual mild steel from hot-extruded clad beryllium. 

Combining volumes, law of, 26, 236 Combustion, heat of hydrogen, 40 Complex ions, 392 amphoteric, 396 bonding in, 395 formation, 413 geometry of. 393 in nature, 396 isomers, 394 linear, 395 octahedral, 393 significance of, 395 square planar, 395 tetrahedral, 394 weak acids, 396 Compound, 28 bonding in, 306 Concentration and equilibrium, 148 and E zero s, 213 and Le Chatelier s Principle, 149 effect on reaction rate, 126, 128 molar, 72... 

It is very instructive to compare the kinetics and plausible mechanisms of reactions catalyzed by the same or related catalyst(s) in aqueous and non-aqueous systems. A catalyst which is sufficiently soluble both in aqueous and in organic solvents (a rather rare situation) can be used in both environments without chemical modifications which could alter its catalytic properties. Even then there may be important differences in the rate and selectivity of a catalytic reaction on going from an organic to an aqueous phase. TTie most important characteristics of water in this context are the following polarity, capability of hydrogen bonding, and self-ionization (amphoteric acid-base nature). 

The basic criterion for distinguishing acids and bases in aqueous solutions is the concentration of hydrogen and hydroxide ions. When an acid dissolves in water, the water acts as a base and accepts protons to form the hydronium ion. Water acts as an acid to produce hydroxide ions when it donates protons to a base dissolved in water. While we can considered water to be amphoteric when it interacts with other acids and bases, we can also consider pure water to be both an acid and base. The reason for this is that water itself actual dissociates to a very... 

The adsorption of dyes to proteins has been studied extensively in the textile industry241. A critically important fact is that acid dyes do not dye cotton242. They can dye wool, silk and other natural proteins. Rattee Breuer have provided considerable information concerning the mechanism of dye interaction with proteins, including amphoteric proteins. Their Chapter 5 discusses the molecular nature of proteins. They have also addressed the subject of hydrogen bonding between dyes and proteins. 

Theoretically, the precipitation of a protein, which is built up of amino-acids and functions as a typical amphoteric electrolyte, should best be accomplished at the isoelectric point, that is, at the hydrogen ion concentration at which the acidic and basic functions of the protein are equal and at a minimum. According to Soerensen, the iso-electric point of egg albumin is at pH 4.8,10 and while precipitation would undoubtedly be most complete at this point, it is not necessarily the most favorable for crystallization, as the egg albumin crystals are not isoelectric protein, but a compound of this with the sulfate ion, and perhaps the ammonium ion as well.11... 

Kai and Ka2 values are frequently tabulated for amino acids (see Table C.l in Appendix C). The values listed represent the successive ionization of the protonated form (i.e., the conjugate acid of the zwitterion) it ionizes to give first the amphoteric zwitterion and second to give the conjugate base, which is the same as a salt of a weak acid that hydrolyzes. Acid-base equilibria of amino acids are therefore treated just as for any other diprotic acid. The hydrogen ion concentration of the zwitterion is calculated in the same way as for any amphoteric salt, such as HC03, as we described in Chapter 7 that is. 

This ability to act as a base or an acid is called amphoterism. Any anions of polyprotic acids, such as HCO3, H2P04, and HP04, which contain replaceable hydrogen ions, are amphoteric. Some hydroxides, such as A1(0H)3 and Zn(OH)2, are also amphoteric, reacting with a base or acid, as illustrated by the following equations ... 

Figure 3.15 Transport number of hydrogen ions relative to sodium ions (PNaH) and current efficiency of cations to the composition of an amphoteric ion exchange membrane. (O, ) quarternized membranes (N-methyl pyridinium and sulfonic acid groups) (A, A) tertiary amino groups membrane (pyridinium hydrochloride and sulfonic acid groups) (, A) PNa 11 (O, A) current efficiency (%). Electrodialysis was carried out at a current density of 20 mA cm 2 using a mixed solution of 0.25 N sodium chloride and 0.25 N hydrochloric acid for 60 min at 25.0 °C.

Anions containing hydrogen (for example, HCOj" and H2P04 ) show amphoteric behaviour when reacting with other acids or bases. Write equations illustrating the amphoterism of these anions. 

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