Solubility coefficient definition

Treatment of class (c) membranes, on the other hand, presents a considerably more complicated problem. Here, S and DT in Eqs. (1) and (2) are functions of the spatial coordinates. The problem becomes much more acute if S and DT are also dependent on C 4,5). Under these conditions, transformation of Eqs. (2) into (3) is not generally possible and there are no standard methods, as in the previous cases, of fully characterizing the membrane-penetrant system 3 "5). There is usually no difficulty in determining an overall or effective solubility coefficient but the definition of useful effective diffusion coefficients is a more difficult matter, which, not surprisingly, is a major concern of current research in the field. 

Polyethylene terephthalate) (PET), with an oxygen permeability of 8 iiiuol/(ius-GPa), is not considered a barrier polymer by die old definition however, it is an adequate barrier polymer for holding carbon dioxide in a 2-L bottle for carbonated soft drinks. The solubility coefficients for carbon dioxide are much larger than for oxygen. For the case of the PET soft drink bottle, the principal mechanism for loss of carbon dioxide is by sorption in the bottle walls as 500 kPa (5 atm) of carbon dioxide equilibrates with the polymer. For an average wall thickness of 370 pm (14.5 mil) and a permeabdity of 40 nmol/(m-s-GPa), many months are required to lose enough carbon dioxide (15% of initial) to be objectionable. 

The dimensionless partition coefficient K = cp/cl = Sr, also known as a relative solubility coefficient, is defined as the ratio of the concentration of a substance in the polymer cP to that in the liquid (food) cLat equilibrium. While D is practically independent of the liquid phase in contact with the polymer in these measurements, the K values are determined by the nature of the polymer and liquid contact phases. From the definition Sr = K, a relative peremeability coefficient can be calculated, Pr = Sr D, with the dimension D. Here, accordingly to Eq. (9-2) and the solubility constant in the polymer and in the liquid phases expressed as SP = cP/p and Sl = C Jp, respectively, the following relationship results between the absolute and relative permeability coefficients ... 

The concentration of dissolved CO2 includes the small amount of undissociated (dissolved) carbonic acid. It can be expressed as cdC02 = a x PCO2, where a is the solubility coefficient for CO2. CHCO3 then represents ctC02 minus cdC02, which includes carbonic acid. The bicarbonate concentration by this definition includes undissociated sodium bicarbonate, carbonate (NaCOs) and carbamate (carbamino-C02 RCNHCOO ), which are present in exceedingly small amounts in plasma. 

The driving force of a membrane for gas separation is the pressure difference across the membrane. The yield of the separated gas can be expressed in terms of membrane permeance, which can be characterised by the amount of permeated gas that passes through a certain membrane area in a given time at a definite pressure difference. The values of permeability are often quoted in Barter (1 Barter=10 cm s cm cm Hg = 3.35 x 10 mol m m s Pa STP, standard temperature and pressure). Gas permeation phenomena can be described by a simple solution diffusion model, which involves (l) sorption or dissolution of the permeating gas in the membrane at the higher pressure side, (2) diffusion through the membrane and (3) desorption or dissolution at the lower pressure side. Thus, the permeability coefficient P can be determined by the product of the solubility coefficient S and the mutual diffusion coefficient D [eqn (5.1)] ... 

Permeability is defined as the product of the diffusion constant and the solubility coefficient. Water vapor permeability (WVP] is defined as the time rate of water vapor transmission through unit area of flat material with a definite unit thickness induced by unit vapor pressure difference between two specific surfaces, and under indicated temperature and humidity conditions. (ASTM E 96, Standard Test Method for Water Vapor Transmission of Materials]. 

The solubilities of gases in liquids may be expressed in various ways. In the definition of the Bunsen coefficient the solubility is expressed as the volume of the ideal gas reduced to O C and 1 atm pressure soluble in a unit volume of liquid under the gas pressure of 1 atm and at the temperature of measurement. The Ostwald solubility ki — Vgl V oiy is defined as the ratio of the volume of absorbed gas to the volume of the absorbing liquid, measured at the same temperature. The Bunsen solubility coefficient a and the Ostwald coefficient L on the assumption of ideal gas behavior are related to the simple g-moles/liter concentration scale c by the relationships which are applicable when P = 1 atm ... 

Special care has to be taken if the polymer is only soluble in a solvent mixture or if a certain property, e.g., a definite value of the second virial coefficient, needs to be adjusted by adding another solvent. In this case the analysis is complicated due to the different refractive indices of the solvent components [32]. In case of a binary solvent mixture we find, that formally Equation (42) is still valid. The refractive index increment needs to be replaced by an increment accounting for a complex formation of the polymer and the solvent mixture, when one of the solvents adsorbs preferentially on the polymer. Instead of measuring the true molar mass Mw the apparent molar mass Mapp is measured. How large the difference is depends on the difference between the refractive index increments ([dn/dc) — (dn/dc)A>0. (dn/dc)fl is the increment determined in the mixed solvents in osmotic equilibrium, while (dn/dc)A0 is determined for infinite dilution of the polymer in solvent A. For clarity we omitted the fixed parameters such as temperature, T, and pressure, p. 

The correlation (or lack of correlation) of other physiochemical characteristics has not yet been established. For instance, are all surfactants irritants Can one classify severity by the size of the molecule Can octanol water partition coefficients predict irritation potential does a propensity to partition out of the ocular fluid mean that a compound presents more of an irritation hazard than one which is more water soluble Theoretically, these data should reflect the ability of a compound to penetrate the eye and cause an irreversible lesion. However, until definitive data are available, physical and chemical parameters will probably have limited utility in an overall assessment of irritation. 

K generally varies only by factors of three to five for a given solute (12). K typically correlates well with physico-chemical properties of the sorbate, such as aqueous solubility (S) or the octanol-water partition coefficient (K ), again suggesting that hydrophobic interaction predominates. The correlation of Koc with K has led to the definition of linear free-energy relationships (LFER) of the form... 

Sigma (a) bonds Sigma bonds have the orbital overlap on a line drawn between the two nuclei, simple cubic unit cell The simple cubic unit cell has particles located at the corners of a simple cube, single displacement (replacement) reactions Single displacement reactions are reactions in which atoms of an element replace the atoms of another element in a compound, solid A solid is a state of matter that has both a definite shape and a definite volume, solubility product constant (/ p) The solubility product constant is the equilibrium constant associated with sparingly soluble salts and is the product of the ionic concentrations, each one raised to the power of the coefficient in the balanced chemical equation, solute The solute is the component of the solution that is there in smallest amount, solution A solution is defined as a homogeneous mixture composed of solvent and one or more solutes. 

A system with clearly defined disperse (A) and continuous (B) component phases is afforded by copolymers of styrene (A) grafted onto a polydimethyl siloxane matrix (B)101 Lack of appreciable interaction between the components was indicated by gas solubility and Tg measurements. The permeability coefficient of propane and other paraffins over a composition range vA = 0 — 0.55 followed the trend described by Eqs. (30)—(33) (with PA = 0, in view of the fact that the polystyrene phase is practically impermeable). Of particular relevance to the present discussion is the close agreement with the Bruggeman, and definite deviation from the Bottcher, equations at higher vA (cf. Fig. 11). Corresponding block copolymer membranes with vA = 0.34 also fitted into this pattern, except in one case where the structure was found to be lamellar and P was considerably lower. 

Note that when water is added to CaSO f Os, the latter dissolves until its rate of dissolution is equal to its rate of precipitation. This is, by definition, the chemical equilibrium point. If, at this point, a certain amount of NaCl (a very water-soluble salt) is added, it suppresses the single-ion activity coefficient of Ca2+ and SO2". Hence, the... 

The compound [Pt(terpy)(SCH2CH20H)]N03 is a dark red-purple microcrystalline material that is extremely water soluble. The complex is stable in cold aqueous solution for periods up to several weeks. High pH or heating (T >60°) leads to decomposition, however. The electronic absorption spectra of the ter-pyridine thiolato compounds are characteristically definitive in the 300-350 nm region and may be used to determine product purity. Solutions of [Pt(terpy)-(SCH2 CH2 OH)] N03 of less than 15 pM obey Beer s law and exhibit the following absorption maxima and molar extinction coefficients 475 (890), 342 (12,900), 327 (10,700), 311 (10,300), 277 (20,300), and 242 (28,700) nm. 

Palytoxin is a white, amorphous, hydroscopic solid that has not yet been crystallized. It is insoluble in nonpolar solvents such as chlorophorm, ether, and acetone sparingly soluble in methanol and ethanol and soluble in pyridine, dimethyl sulfoxide, and water. The partition coefficient for the distribution of palytoxin between 1-butanol and water is 0.21 at 25°C based on comparison of the absorbance at 263 nm for the two layers. In aqueous solutions, palytoxin foams on agitation, like a steroidal saponin, probably because of its amphipathic nature. The toxin shows no definite melting point and is resistant to heat but chars at 300°C. It is an optically active compound, having a specific rotation of -i-26° 2° in water. The optical rotatory dispersion curve of palytoxin exhibits a positive Cotton effect with [a]25o being -i-700° and [a]2,j being +600° (Moore and Scheuer 1971 Tan and Lau 2000). 

Activity Coefficients from Solubility Measurements.—The activity coefficient of a sparingly soluble salt can be determined in the presence of other electrolytes by making use of the solubility product principle. In addition to the equations already given, this principle may be stated in still another form by introducing the definition of the mean ionic concentration, i.e., c , which is equal to c+clr, into equation (109) this equation then becomes... 

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