Water amphoteric nature

Sn02, cassiterite, is the main ore of tin and it crystallizes with a rutile-type structure (p. 961). It is insoluble in water and dilute acids or alkalis but dissolves readily in fused alkali hydroxides to form stannates M Sn(OH)6. Conversely, aqueous solutions of tin(IV) salts hydrolyse to give a white precipitate of hydrous tin(IV) oxide which is readily soluble in both acids and alkalis thereby demonstrating the amphoteric nature of tin(IV). Sn(OH)4 itself is not known, but a reproducible product of empirical formula Sn02.H20 can be obtained by drying the hydrous gel at 110°, and further dehydration... 

Water is amphoteric. It will act as either an acid or a base, depending upon whether the other species is a base or acid. In pure water, we find the same amphoteric nature. In pure water, a very small amount of proton transfer is taking place ... 

Before examining the equilibrium behavior of aqueous solutions of weak bases, let s look at the behavior of water itself. In the initial discussion of acid—base equilibrium above, we showed water acting both as an acid (proton donor when put with a base) and a base (proton acceptor when put with an acid). Water is amphoteric, it will act as either an acid or a base, depending on whether the other species is a base or acid. But in pure water the same amphoteric nature is noted. In pure water a very small amount of proton transfer is taking place ... 

The data for TUB hydroxide solubility in different media have recently receive a great deal of attention due to their importance for development of clean-up technologies, etc. It is known that the Pu(OH)3 solubility in water and 5M ammonium solution is equal to 7.5 10 M and 3.8 10 " M, respectively [12]. The solubility product of the Pu(III) hydroxide is about 2 10 ° [13,14]. According to the data of different authors, the solubility products of Pu(OH)3 and Am(OH)3 hydroxides are equal to about 10 [15]. The solubility of Pu(III) hydroxide in 5M NH4OH is 3.8 10"" M [16], and the solubility of Am(III) in 0.01-5M NH4OH is 1.6 10" M [17]. The suggested chemical form of these alkali-dissolved hydroxides is a neutral Am(OH)3-type molecule, which does not tend to have an amphoteric nature or to form complexes with OH" ions. Despite the low solubility of TUE(III) hydroxides, in the crystalline form they can be easily dissolved. Thus, the concentration of the Am(OH)3 and Cm(OH)3 colloid solutions may exceed more than 100 g/L [4]. 

Hydroxyl (serine) and sulfhydryl groups (cysteine) are also silylated. These derivatives can be used in peptide synthesis by the phosphoryl chloride, imidazole, mixed anhydride, or p-nitrophenyl ester methods. An attractive feature is that the silyl groups are removed merely by treatment with water in the normal workup. Trimethylchlorosilane is not suitable because of the amphoteric nature of the amino acids. 

As we have seen, whether a particular substance behaves as an acid or as a base depends on its environment. Earlier we described the amphiprotic nature of water. Amphoterism is a more general term that describes the ability of a substance to react either as an acid or as a base. Amphiprotic behavior describes the cases in which substances exhibit amphoterism by accepting and by donating a proton, H+. Several insoluble metal hydroxides are amphoteric that is, they react with acids to form salts and water, but they also dissolve in and react with excess strong bases. 

We see that in this instance water acts like an acid, and that, therefore, it is able to split off protons as well as to take them up. This amphoteric nature characterizes a number of other solvents such as alcohol, ammonia, acetic acid, formic acid, pyridine, aniline, and sulfuric acid. The dual nature of water may be described as follows ... 

Many different complexes of elements in a given oxidation state may exist in water. The amphoteric nature of Al(III) and Fe(III) results from the formation of a series of dissolved species, MOH, M(OH)J, M(0H)3, and other forms, in addition to the more common M ". The speciation of soluble A1 and Fe is thus a sensitive function of pH. 

Some oxides and hydroxides are able to react with both acids and bases, thereby functioning as both bases and acids, respectively. Water is probably the most common example, but in this section we consider the amphoteric nature of metal oxides and hydroxides. Aluminium oxide, AI2O3, reacts with acids (equation 6.39) and with hydroxide ion (equation 6.40). 

The pH of an aqueous slurry of carbons represents the average chemistry of the carbon surface. Bronsted acidic groups of the carbon surface tend to donate their protons to water molecules, and hence the surface becomes negatively charged while Lewis bases adsorb protons from solution, becoming positively charged. Thus, various surface functionalities are responsible for the amphoteric nature of carbon, the pH in aqueous solution, and its surface charge. To estimate the surface... 

The oxides and hydroxides of the metals of Group 3 and higher tend to be only weakly basic, and most display an amphoteric nature. Most of these compounds are so slightly soluble in water that their acidic or basic character is only obvious in their reactions with strong acids or bases. 

This lead compound exists in two polymorphic forms tetragonal (P-PbO) and orthorhombic (a-PbO). The solubility of the two forms in water at 25 °C is 0.0504 g for a-PbO and 0.1065 g for 3-PbO [6]. Lead oxide forms lead hydroxides, 3Pb0-H20 and 5PbO H2O [7,8]. Lead oxide is hydrated forming Pb(OH)2, a compound of amphoteric nature. It dissociates to HPb02 and Pb(OH) ions. In the battery industry, lead oxide is obtained by partial thermal oxidation of lead and is ealled leady oxide , as it eontains between 73% and 85% PbO, the remaining part being non-oxidized lead. The basie eonstituent of leady oxide is tet-PbO, but orthorhombie PbO is also present, up to 5—6%. Leady oxide is used for tbe preparation of the pastes for lead—aeid battery plate production. 

According to their amphoteric nature, aluminum hydroxides have their minimum solubdity in water at a close-to-neutral pH value, that is, in the pH range of 6—7. At a pH larger than 8.5, the solubihty increases, and the [A1(0H)4] anion is formed. At a pH smaller than 4, the aquo cation [A1(0H2)6] is reported to be predominant, whereas at a pH between 4 and 6, its dissociated form [Al(OH2)5(OH)] prevails (36,37), likely both with less tightly bound water molecules in the secondary hydration shell. However, the speciation of aluminum in aqueous environments is very complicated. Depending on the conditions, such as pH, concentration (or hydrolysis ratio), and anions present, a variety of polynuclear species can be found in solution. In pure water, polynuclear species include dimers... 

A primary requirement in all solvation studies is the analytical examination of the solvent and the solute. Since water, owing to its amphoteric nature, behaves as a base in acidic solvents and as an acid in basic solvents, strongly solvating both Lewis acids and Lewis bases as a consequence of its ability to donate an electron pair and to form hydrogen bonds, the first and perhaps the most important task of the analyst is to determine the moisture contents of the solvent, of the components to be dissolved, and finally of the solution. This is followed by the detection, and if necessary the determination, of any possible decomposition products of the solvent. 

As discussed in Section 6.2.5, water and alcohols are amphoteric compounds that function as either an acid or a base under the proper conditions. The reactions of ethanol (12) as both an acid and a base were discussed in that section, in the context of the amphoteric nature of alcohols. Ethers are molecules with two alkyl groups flanking oxygen and they have no acidic protons. Ethers are weak acids because all hydrogen atoms are attached to carbon rather than oxygen. However, the oxygen atoms of ethers react as bases. Diethyl ether (44) is a typical acyclic ether. The nomenclature for ethers is presented in Chapter 5, Section 5.6.4. 

Chem. Descrip. Sodium laureth sulfate, sodium lauryl sulfate, cocamidopropyl betaine, cocamide DEA, glycol stearate, hexylene glycol, water Ionic Nature Anionicfnonionic/amphoteric... 

As mentioned above, the increased importance of the imidazoline-derived surfactants stems primarily from their mildness and low toxicity. The extent of their use in shampoos and body care products has followed closely the overall increase in the use of such products worldwide. Their amphoteric nature also makes them useful in a wide range of water types, ranging from hard to soft water and high to low pH. Such flexibility makes them useful in cleaning formulations that will see a variety of conditions. 

Manganese Hydroxide. Manganese hydroxide [18933-05-6] is a weaMy amphoteric base having low solubihty in water. Mn(OH)2 crystals are reported to be almost pure white and darken on exposure to air. Manganese dihydroxide occurs in nature as the mineral pyrochroite and can also be prepared synthetically by reaction of manganese chloride and potassium hydroxide that is scmpulously free of oxygen. The entire reaction is conducted under reducing conditions (36). 

Like the natural gums, starches need to be cooked in water to form dispersions for addition to the papermaking system. Various techniques have been developed for cooking starches rapidly (see Starch). In general, anionic starches are used with alum, which aids in starch retention. The cationic and usually the amphoteric starches are self-retaining. 

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