Hydration variability

Typically, when the cations are introduced they are hydrated. Variable amounts of water are represented by modification of this formula to also include an .mH20 term. A schematic diagram of a zeolite structure with cavities and cations is shown in Figure 7.12. 

All that can be concluded from the data given in the preceding example is that the particle is not an unsolvated sphere. However, when an appropriate display of contours is examined for f/fo (e.g.. Ref. 2), the latter is found to be consistent with an unsolvated particle of axial ratio about 4 1 or with a spherical particle hydrated to the extent of about 0.48 g water (g polymer). Of course, there are a number of combinations of these variables which are also possible, and some additional experimental data—such as the intrinsic viscosity—are needed to select that combination which is consistent with all experimental observations. 

Mag nesia. ndAlumina. Suspension. A mixture of salts, available as Maalox, Mylanta, Gelusil, and Aludrox, contains magnesium hydroxide [1309-42-8] Mg(OH)2, and variable amounts of aluminum oxide in the form of aluminum hydroxide and hydrated aluminum oxide, ie, 2.9—4.2% magnesium hydroxide and 2.0—2.4% aluminum oxide, Al O, for a mixture of 4.9—6.6% combined magnesium hydroxide and aluminum oxide. This mixture may contain a flavoring and antimicrobial agents in a total amount not to exceed 0.5% (see Aluminum compounds, aluminum oxide). 

X 10 J/T (5.71 //g) at room temperature. It is air stable at 25°C, but is slowly converted to Fe202 and bromine at 310°C. The light yellow to brown hydroscopic sohd is soluble ia water, alcohol, ether, and acetonitrile. Iron(II) bromide forms adducts with a wide range of donor molecules. Pale green nona-, hexa-, tetra-, and dihydrate species can be crystallized from aqueous solutions at different temperatures. A hydrate of variable water content,... 

Tricalcium phosphate, Ca2(P0 2> is formed under high temperatures and is unstable toward reaction with moisture below 100°C. The high temperature mineral whidockite [64418-26-4] although often described as P-tricalcium phosphate, is not pure. Whidockite contains small amounts of iron and magnesium. Commercial tricalcium phosphate prepared by the reaction of phosphoric acid and a hydrated lime slurry consists of amorphous or poody crystalline basic calcium phosphates close to the hydroxyapatite composition and has a Ca/P ratio of approximately 3 2. Because this mole ratio can vary widely (1.3—2.0), free lime, calcium hydroxide, and dicalcium phosphate may be present in variable proportion. The highly insoluble basic calcium phosphates precipitate as fine particles, mosdy less than a few micrometers in diameter. The surface area of precipitated hydroxyapatite is approximately... 

Over 50 acidic, basic, and neutral aluminum sulfate hydrates have been reported. Only a few of these are well characterized because the exact compositions depend on conditions of precipitation from solution. Variables such as supersaturation, nucleation and crystal growth rates, occlusion, nonequilihrium conditions, and hydrolysis can each play a role ia the final composition. Commercial dry alum is likely not a single crystalline hydrate, but rather it contains significant amounts of amorphous material. 

Hydrated Stannic Oxide. Hydrated stannic oxide of variable water content is obtained by the hydrolysis of stannates. Acidification of a sodium stannate solution precipitates the hydrate as a flocculent white mass. The colloidal solution, which is obtained by washing the mass free of water-soluble ions and peptization with potassium hydroxide, is stable below 50°C and forms the basis for the patented Tin Sol process for replenishing tin in staimate tin-plating baths. A similar type of solution (Staimasol A and B) is prepared by the direct electrolysis of concentrated potassium staimate solutions (26). 

In general, hydrated borates of heavy metals ate prepared by mixing aqueous solutions or suspensions of the metal oxides, sulfates, or halides and boric acid or alkali metal borates such as borax. The precipitates formed from basic solutions are often sparingly-soluble amorphous soHds having variable compositions. Crystalline products are generally obtained from slightly acidic solutions. 

Calcium siHcate hydrate is not only variable ia composition, but is very poody crystallised, and is generally referred to as calcium siHcate hydrate gel or tobermorite gel because of the coUoidal sizes (<0.1 fiva) of the gel particles. The calcium siHcate hydrates ate layer minerals having many similarities to the limited swelling clay minerals found ia nature. The layers are bonded together by excess lime and iatedayer water to form iadividual gel particles only 2—3 layers thick. Surface forces, and excess lime on the particle surfaces, tend to bond these particles together iato aggregations or stacks of the iadividual particles to form the porous gel stmcture. 

The drying mechanisms of desiccants may be classified as foUows Class 1 chemical reaction, which forms either a new compound or a hydrate Class 2 physical absorption with constant relative humidity or vapor pressure (solid + water + saturated solution) Class 3 physical absorption with variable relative humidity or vapor pressure (soHd or liquid + water + diluted solution) and Class 4 physical adsorption. 

Water-Holding Capacity (WHC). AU polysaccharides are hydrophilic and hydrogen bond to variable amounts of water. HydratabUity is a function of the three-dimensional stmcture of the polymer (11) and is kifluenced by other components ki the solvent. Fibrous polymers and porous fiber preparations also absorb water by entrapment. The more highly crystalline fiber components are more difficult to hydrate and have less tendency to sweU. Stmctural features and other factors, including grinding, that decrease crystallinity or alter stmcture, may iacrease hydratioa capacity and solubUity. 

Aluminium fluoride (anhydrous) [7784-18-4] M 84.0, m 250°. Technical material may contain up to 15% alumina, with minor impurities such as aluminium sulfate, cryolite, silica and iron oxide. Reagent grade AIF3 (hydrated) contains only traces of impurities but its water content is very variable (may be up to 40%). It can be dried by calcining at 600-800° in a stream of dry air (some hydrolysis occurs), followed by vacuum distn at low pressure in a graphite system, heated to approximately 925° (condenser at 900°) [Henry and Dreisbach J Am Chem Soc 81 5274 1959]. 

Sodium borate (decahydrate, hydrated borax) [1303-96-4] M 381.2, m 75 (loses 5H2O at 60 ), d 1.73. Crystd from water (3.3mL/g) keeping below 55° to avoid formation of the pentahydrate. Filtered at the pump, washed with water and equilibrated for several days in a desiccator containing an aqueous solution saturated with respect to sucrose and NaCl. Borax can be prepared more quickly (but its water content is somewhat variable) by washing the recrystd material at the pump with water, followed by 95% EtOH, then Et20, and air dried at room temperature for 12-18h on a clock glass. 

Figure 5 Time dependence of RMSD of atomic coordinates from canonical A- and B-DNA forms m two trajectories of a partially hydrated dodecamer duplex. The A and B (A and B coiTespond to A and B forms) trajectories started from the same state and were computed with internal and Cartesian coordinates as independent variables, respectively. (From Ref. 54.)...

Since 17a-ethynyl-17 -hydroxy steroids are so readily prepared, they represent attractive starting materials for conversion to 20-ketopregnanes. Standard methods for the hydration of aliphatic acetylenes (e.g, mercuric salts alone, with aniline, or with BF3) give variable results, and sometimes no product at all, due to D-homo rearrangement. 233,235,265-7 mercury... 

Many salts crystallize from aqueous solution not as the anhydrous compound but as a well-defined hydrate. Still other solid phases have variable quantities of water associated with them, and there is an almost continuous gradation in the degree of association or bonding between the molecules of water and the other components of the crystal. It is convenient to recognise five limiting types of interaction though the boundaries between them are vague... 

There has been considerable discussion about the extent of hydration of the proton and the hydroxide ion in aqueous solution. There is little doubt that this is variable (as for many other ions) and the hydration number derived depends both on the precise definition adopted for this quantity and on the experimental method used to determine it. H30" has definitely been detected by vibration spectroscopy, and by O nmr spectroscopy on a solution of HF/SbFs/Ha O in SO2 a quartet was observed at —15° which collapsed to a singlet on proton decoupling, 7( 0- H) 106 Hz. In crystalline hydrates there are a growing number of well-characterized hydrates of the series H3O+, H5O2+, H7O3+, H9O4+ and H13O6+, i.e. [H(0H2) ]+ n = 1-4, Thus... 

Of the many molybdenum sulfides which have been reported, only MoS, M0S2 and M02S3 are well established. A hydrated form of the trisulfide of somewhat variable composition is precipitated from aqueous molybdate solutions by H2S in classical analytical separations of molybdenum, but it is best prepared by thermal decomposition of the thiomolybdate, (NH4)2MoS4. MoS is formed by heating the calculated amounts of Mo and S in an evacuated tube. The black M0S2, however, is the most stable sulfide and, besides being the principal ore of Mo,... 

Treatment of the hydroxides of Zn and Cd with aqueous H2O2 produces hydrated peroxides of rather variable composition. That of Zn has antiseptic properties and is widely used in cosmetics. 

Both our original prediction about the effect of ionization energy on acid-base behavior and the trend which we have observed in the first three elements lead us to expect that the hydroxide or oxide of silicon should not be basic, but perhaps should be weakly acidic. This is in fact observed. Silicon dioxide, Si02, can exist as a hydrated solid containing variable amounts of water,... 

Recent experiments2 on the equilibrium Hu ice gas at — 3°C in the system HaS-propane-water confirm that these two gases also form mixed hydrates of variable composition, as shown in Fig. 10. In this respect the present system is similar to the system me thane-propane-water of Fig. 7, but unlike the latter it exhibits a minimum pressure (azeotrope). It was further shown that the solution theory of clathrates can account for this interesting phenomenon. For details the reader is referred to ref. 29. 

Al(III) is an example of an aquatic ion that forms a series of hydrated and protonated species. These include AlOrf Al(OH)J, Al(OH)3, and other forms in addition to AP. (For simplicity, we omit the H2O molecules that complete the structures of these complexes.) Most of these species are amphoteric (able to act as an acid or a base). Thus the speciation of Al(III) and many other aquatic ions is sensitive to pH. In this case, an aggregate variable springs from the conservation of mass condition. In the case of dissolved aluminum, the total dissolved aluminum is given by... 

The first term is related to the van der Waals interaction, with A being the Hamaker constant. The second term includes other forces that decay exponentially with distance. As discussed, these may include double-layer, solvation, and hydration forces. In our data analysis, B and C were used as fitting variables the Hamaker constant A was calculated using Lifshitz theory [6]. 

Another variable that influences the saturation solubility of a drug molecule is its degree of solvation. Since the anhydrous, hydrated, and alcoholated forms of a drug have slightly different solubilities, they may well have different dissolution rates and, therefore, different rates of absorption. However, these differences may not be clinically significant [35],... 

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