Water Solvent power

As a solvent, water is powerful yet innocuous. No other chemically inert solvent compares with water for the substances it can dissolve. Also, it is very impor-... 

Test methods for corrosivity of solvent systems for removing water-formed deposits Recommended practice for determining corrosivity of adhesive materials Guide to the selection of test methods for coatings used in light-water nuclear power plants... 

Water forms hydrogen-bonded clusters with itself and with other proton donors or acceptors. Hydrogen bonds account for the surface tension, viscosity, liquid state at room temperature, and solvent power of water. 

Decaffeination of green coffee beans is most usually carried out with a water/solvent partition system. The green coffee beans are first steamed until they are hot, wet, and swollen, to make the caffeine available. Solvent is then used to extract the caffeine out of the aqueous phase of the beans. Finally, the beans are steamed to drive off residual solvent. The coffee beans lose their wax surface covering in the process, as well as some flavor components. For this reason, the Robusta and Brazilian Arabica coffees that are dry-processed and have the most powerful flavors are usually the types that are decaffeinated. They become milder in the process. Mechanical polishing is used to improve the appearance of decaffeinated green coffee beans if they are not to be roasted immediately. Extra care is required, however, to store these decaffeinated beans since the loss of wax covering as well as caffeine renders them much more susceptible to fungal attack. 

Supercritical water also exhibits a very strong solvent power toward most chemical species. This dramatically increased solvating power is due to the sharp increase of the fluid density as well as the polar nature of the fluid. Also, since many organics are completely miscible in supercritical water, the problem of mass transport... 

Although supercritical CO2 is an effective solvent for oils, fats, and similar substances, it is a poor one for nonvolatile hydrophilic (water-loving) substances such as proteins or metallic salts. Adding water as such to the supercritical CO2 is of little help, as the solubility of water in it is limited. Johnson and co-workers216 overcame the latter limitation by forming water-in-C02 emulsions with the aid of an added nontoxic perfluoropolyether surfactant that forms reverse micelles around the water microdroplets, in effect combining the special properties of supercritical CO2 with the solvent power of water. These emulsions can dissolve a variety of biomolecules at near-ambient temperatures, without loss of their biological activity. 

Hydrofluoric acid like water is an associated liquid, and even the gas, as we shall soon see, is associated. It has the power of uniting with fluorides. It also seems to be an ionizing solvent for a soln. of potassium fluoride in liquid hydrogen fluoride is an excellent conductor it also possesses marked solvent powers. According to E. C. Franklin,7 the liquid readily dissolves potassium fluoride, ehloride, and sulphate sodium fluoride, bromide, nitrate, chlorate, and bromate acetamide and urea. The solvent action is not so marked with barium fluoride, cupric chloride, and silver cyanide while calcium and lead fluorides copper sulphate and nitrate ferric chloride, mercuric oxide, and magnesium metal, are virtually insoluble in this menstruum. Glass also is not affected by the liquid if moisture be absent. The liquid scarcely acts on most of the metals or non-metals at ordinary temp., though it does act on the alkali metals at ordinary temp., much the same as does water, with the simultaneous production of flame. 

According to F. C. Franklin and C. A. Kraus,40 liquid ammonia readily dissolves sodium and potassium iodides. The partial press, of ammonia in soln. of potassium iodide at 25°, as measured by R. Abegg and H. Riesenfeld, is raised from 13 45 mm. of water to 13 28, and 14 88 mm. for 0 5W-, N-, and l 5Ar-soln. respectively. H. M. Dawson and J. McCrae have shown that the distribution of ammonia between water and chloroform is generally lowered by the addition of various salts of the alkali metals and ammonium which they tried—halides, nitrates, chlorates, oxalates, sulphates, carbonates, hydroxides this means that the solvent power of aq. soln. of the alkali salts is in general less than that of pure water—lithium chloride, ammonium bromide, and sodium iodide act in the opposite way. The other halide salts of lithium were not tried. The change produced in the partition coeff. by the halides, at 20°, is as follows ... 

The great solvent power of water, especially for ionic compounds, is due to its dielectric constant. If this were only, say 10, instead of the actual 80, it would mean that water could dissolve only a trace of sodium chloride. This solvent action of water., naturally. plays an important role in geology. In biology, water functions as a means of conveying salts and other substances which circulate in the bodies of animals and plants. It is outside the scope of this book to discuss any further the function of water on this planet, a subject which could fill many volumes. It is important in this context that we now know water molecules to possess a dipole moment and to discover whether perhaps this fact can provide an explanation of the unique properties of water. 

In alcohols, water is found to be partially displaced, and it is possible to have the water/salt ratio in a saturated solution considerably less than that in the hydrated solid in equilibrium with it (4> 10). As with pyridine, an alcohol in a heterogeneous system will sometimes displace water well enough to make the difference between extraction and nonextraction of a metal-ion value (29). Another way in which the differences between strong water-competitors such as alcohol and weaker competitors such as the ketones and ethers are manifested is when liquid such as CC14, with no solvent power of its own for the salt, is mixed with the oxygenated solvent. With thorium nitrate as the test salt, it is seen (Fig. 2) that, whereas addition... 

Id) Solubility Slightly soluble in water (1 g/350 mL at 25°C) miscible with methanol, ethanol, benzene, diethyl ether, petroleum ether, carbon tetrachloride, chloroform, carbon disulfide, dimethylformamide and oils. Has the highest solvent power of the chlorinated hydrocarbons (Lide, 1995 Budavari, 1996)... 

In some a)kali works, to assist the solvent power of tho water employed in tho Iixiviation of black ash, it is usual to heat it to about 90° to 100°. This end may ho conveniently attained by passing the water through a coil cf pipes Contained in a steam boiler. The practice of heating the water, though it undoubtedly aids the process of Iixiviation, is nevertheless very objectionable, principally because sulphide of calcium is dissolved and decomposed by hot water, giving rise to the formation of sulphide of sodium, and the hotter the water tho greater Will this proportion of sulphida be, or rather of the donble sulphide of sodium and iron contained in the vat liquor. 

Take first one pound of vitriol of Cyprus and a half pound of salpeter and a quarter pound of laminated alum and extract the water at the red heat of the alembic, for the solvent power is great, and make use of it in the fore-mentioned chapters it will be made much sharper if you dissolve with that a fourth part of sal ammoniac, because it then dissolves gold, sulphur and silver. ... 

The separation in the isobaric decaffeination processes is executed with absorption of caffeine, that means, the caffeine dissolved in CO2 is carried over into water by means of a packed washing column, or by adsorption with activated charcoal, but without recovery therefrom. Other separation methods under investigation are the use of membranes, since the difference in molecular weight between extract and solvent is high enough, or by the addition of substances of low solvent power. It is questionable whether the advantage of the possible isobaric process can compensate for the investment for the additional process steps required. 

The term solvent action is understood (o mean any process of making substances water soluble but in a broader interpretation the term is understood to be the phenomenon of making a substance soluble in a solvent. Solvent power, diluting power, solvency and similar expressions indicate the property of solvents to disperse the molecules of a solute or vehicle therehy causing a decrease in viscosity. 

The most common solvent is water. Water dissolves a great many gases, liquids, and solids, and is much used for this purpose. Other liquids similarly dissolve many substances without reacting chemically with them. Important considerations in connection wfith the choice of solvent for a given case are (1) vapor pressure and boiling point, (2) solvent power under stated conditions of temperature. (3) ease and completeness of recoverability by evaporation and condensation, and completeness of separation from dissolved material by evaporation. (4) heat of vaporization, (5) miscibility with water or other liquid, if present, (6) inertness to chemical reaction with the materials present, and with the apparatus, (7) inflammability and explosiveness. (8) odor and toxicity (9) cost of solvent, loss in process, cost of recovering. 

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