WATER—A UNIQUE SOLVENT

Water is a vitally important solvent in environmental chemistry, green chemistry, and industrial processes. Those properties of water that relate directly to its characteristics as a solvent are summarized in this chapter. 

At room temperature H2O is a colorless, tasteless, odorless liquid. It boils at 100°C (212°F) and freezes at 0°C (32°F). Water by itself is a very stable compound it is very difficult to break up by heating. However, as explained in Section 8.6, when electrically conducting ions are present in water, a current may be passed through the water, causing it to break up into Hj gas and O2 gas. 

Water is an excellent solvent for a variety of materials these include many ionic compounds (acids, bases, and salts). Some gases dissolve well in water, particularly those that react with it chemically. Sugars and many other biologically important compounds are also soluble in water. However, greases and oils generally are not soluble in water but do dissolve in organic solvents. 

Some of water s solvent properties can best be understood by considering the structure and bonding of the water molecule  

The water molecule is made up of two hydrogen atoms bonded to an oxygen atom. The three atoms are not in a straight line, but form an angle of 105°, 

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Water is a unique solvent because of its high polarity and ability to form a network of H-bonds. It is immiscible with many organic solvents and is therefore a suitable solvent for use in biphasic reactions in which catalysts are made preferentially soluble in the aqueous phase. Phase transfer catalysis allows the use of aqueous reagents with substrates that have low solubility in water. That water is abundant and totally non-toxic make it the perfect clean solvent, provided that solubility issues can be overcome, and it is in use as a solvent on an industrial scale for polymerization, hydroformylation, and a range of organic chemistry involving PTC. These applications are discussed further in Chapters 7-11. 

That the traits of B. m aterium can be transferred to B. subtilis by plasmid transfer techniques has been established. These traits are increased resistance to naphthalene, parachlorbiphenyl, and dibenzofuran, and increased ability to degrade C-naphthalene. The transformants increased degradative abilities were demonstrated by the accumulation of greater quantitites of water soluble metabolite and the presence of a unique solvent soluble metabolite. 

Water is a unique solvent, which also happens to be ubiquitous to life on Earth. Paradoxical as it may seem, any discussion on enzymatic catalysis in organic sol-... 

For the same reason as above, excess solvent molecules in the cavitation bubble also seriously limit the applicability of many volatile organic solvents as a medium for sonochemical reactions [2,25,26]. In fact, water becomes a unique solvent in many cases, combining its low vapor pressure, high surface tension, and viscosity with a high yield of active radical output in solution. Its higher cavitation threshold results in subsequently higher final temperatures and pressures upon bubble collapse. Most environmental remediation problems deal with aqueous solutions, whereas organic solvents are mostly used in synthesis and polymer modifications processes. 

Water, as we know, is a unique solvent. One of its special properties is its ability to act either as an acid and as a base. Water functions as a base in reactions with acids such as HCI and CH3COOH, and it functions as an acid in reactions with bases such as NH3. Water is a very weak electrolyte and therefore a poor conductor of electricity, but it does undergo ionization to a small extent ... 

There is no other ingredient more essential to BU than water. All life as we know it, is water based. Water is essential to life because it is a unique solvent that forms the medium in which to transport many other substances, both organic and inorganic, ionized and nonionized (Section 3.2.4). 

Thus, the extended network of H2O molecules in liquid water is a fluctuating network [4]. This fluctuation lets water be responsive to foreign solutes because it allows water to easily rearrange and solvate a large variety of solutes. This feature partly allows water to act as a unique solvent. 

A less sophisticated source of contamination by a solute occurs in plant cleaning, where solvent power for any contaminant is of primary importance but where water miscibility, so that cleaning and drying take place in a single operation, is also an important property. Low toxicity is also desirable if draining or blowing out the cleaned equipment is also involved. In this case there is seldom a unique solvent that will fulfil the requirements, and ease of recovery can be an important factor in the choice. 

Water ean usually be used as a unique solvent for the study of biomedical materials. In other applications such as reverse-phase liquid chromatography, however, different solvents such as water-methanol mixed solvents are used. As the MeOH fraction increases, the surface tension of the solution decreases. In mixed solvents, the trend of contact angles as a function of concentration was generally similar to that of the aqueous case. As the proportion of methanol increases, the contact angle deereases dramatically as in the case of decreased concentration. 

The host-guest association process, incorporating structured solvent molecules (with water as the best example), is illustrated in Scheme 4. It is widely recognized that water is a unique solvent capable of playing active roles in supramolecular and biological recognition processes the detailed information and discussion on this topic may be found in a recent review. ... 

Butyl glycol is a unique solvent in that it is not truly water soluble. At about 4S-S0°C a butyl glycol, water mixture will go cloudy indicating immiscibility/insolubility. Below these temperatures the solution is clear. However, when a third component is present this is not a problem because it normally helps solubilise the butyl glycol. An explanation for the partial water solubility is that butyl glycol consists of both hydrophobic and hydrophillic constituents and is of a sufficiently high molecular weight for them both to have an effect. 

Aramid Fibers. Aromatic polyamide fibers exhibiting a range of mechanical properties are available from several manufacturers, perhaps the best known being Du Pont s proprietary fiber Kevlar. These fibers possess many unique properties, such as high specific tensile strength and modulus (see Fig. 4). Aramid fibers have good chemical resistance to water, hydrocarbons, and solvents. They also show excellent flame retardant characteristics (see High PERFORMANCE fibers Polyamdes). 

Besides these special physical properties, hydrogen-bonded liquid water also has unique solvent and solution properties. One feature is high proton (H ) mobility due to the ability of individual hydrogen nuclei to jump from one water molecule to the next. Recalling that at temperatures of about 300 K, the molar concentration in pure water of H3O ions is ca. 10 M, the "extra" proton can come from either of two water molecules. This freedom of to transfer from one to an adjacent "parent" molecule allows relatively high electrical conductivity. A proton added at one point in an aqueous solution causes a domino effect, because the initiating proton has only a short distance to travel to cause one to pop out somewhere else. 

Ordinary water behaves very differently under high temperature and high pressure. Early studies of aqueous solutions under high pressure showed a unique anomaly that was not observed with any other solvent.11 The electrolytic conductance of aqueous solutions increases with an increase in pressure. The effect is more pronounced at lower... 

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