Moderately concentrated solution

This involves the Flory-Huggins parameter x and hence assumes the same limitation as the rest of the Flory-Huggins approach, i.e. a moderately concentrated solution. Flory and Krigbaum rewrote this equation in terms of some other parameters, i.e. 

Experiments—Carbon dioxide is passed into a moderately concentrated solution of /3-naphthol in sodium hydroxide solution until the free naphthol is precipitated. 

The final goal of all attempts is a description, and hopefully also a reliable prediction, of the macromolecular properties in bulk and in moderately concentrated solutions. It may be useful to recall that even the polymerization processes are conducted either in the melt or in fairly concentrated solutions. Under such conditions a complex interplay between the structures of the individual macro-molecules with strong mutual interactions takes place. In order to disentangle the complexity it will be helpful to derive at first a precise picture of the structure of individual macromolecules. Their properties can most adequately be studied... 

Therefore, the distribution ratio of B remains constant only if the ratio of the activity coefficients is independent of the total concentration of B in the system, which holds approximately in dilute solutions. Thus, although solutions of metal chelates in water or nonpolar organic solvents may be quite nonideal, Nernst s law may still be practically obeyed for them if their concentrations are very low (JCchehte< 10" ). Deviations from Nernst s law (constant D ) will in general take place in moderately concentrated solutions, which are of particular importance for industrial solvent extraction (see Chapter 12). 

Figure 9.13. Schematic representation of matrix polymerization of urea and formaldehyde in the presence of PAA (a) moderately concentrated solution of PAA and monomers (monomer molecules are not indicated), (b) 1st step of the process - gel formation (composite polycomplex + excess of PAA), (c) polycomplex PAA-PFU =1 1, (d) composite polycomplex + excess of PFU. Reprinted from I. M. Papisov, 0. E. Kuzovleva, S. V. Markov and A. A. Litmanovich, Eur. PoZy/n. J.,20,195(1984),...

Lead rhodanate, Pb(CNS)2 is formed, when a solution of lead nitrate, slightly acidified with nitric acid, is treated with a moderately concentrated solution of the rhodanate of an alkali metal. 

Common commercial crystallized carbon a ta of soda contains a still greater proportion of water titan the salt last named. These crystals are a combination of ono equivalent of carbonate of soda with ten equivalent of water, and are consequently represented by the foimula Na 0, CO, 10HO. They are formed from a moderately concentrated solution, at a temperature below 92°. Their crystelline form is that of tho oblique prism.. . 

Cornet, C.F. The determination of unperturbed dimensions of polymer molecules by viscometry of moderately concentrated solutions. Polymer (London) 6, 373-384 (1965). 

The pure acid has not been isolated, but the moderately concentrated solution is an odourless, dear, slightly viscous liquid, which is not very strongly acidic, although it possesses an acid taste. The heat of formation1 of the acid from its elements is given by the equation ... 

Although the quantitative theory of reactions in moderately concentrated solutions of strong acids is unsatisfactory, we do have a good qualitative idea of the processes involved in the acid-catalyzed hydrolysis and formation of esters. Under conditions where the degree of protonation of the substrate is small it is not possible to separate with confidence the factors which affect the solvolytic process and those which affect the preliminary protonation equilibrium. But there have been a number of recent studies of t ie behaviour of carboxylic acids and esters in very strongly acidic media, in. which they are essentially completely protonated. Under these conditions it is possible to observe the behaviour of the protonated species directly. It is appropriate to summarize the results of this research before discussing the reactions under more normal solvolytic conditions. 

A series of double compounds of arsenious oxide and the iodides of bivalent light and heavy metals has been described.6 The compounds are obtained in crystalline form by saturating hot moderately concentrated solutions of the iodides with arsenious oxide and allowing to cool. The following have been prepared ... 

Arsenic pentasulphide may also be prepared from aqueous arsenic acid or a solution of an arsenate by the action of hydrogen sulphide, but the nature of the product depends upon conditions. Berzelius reported 2 the formation of the pentasulphide when the gas acted on a moderately concentrated solution of arsenic acid, but Wackenroder stated 3 that the arsenic acid was first reduced by hydrogen sulphide to arsenious acid, even in the presence of hydrochloric acid, and that a mixture of arsenic trisulphide and sulphur was then precipitated. Rose,4 after passing hydrogen sulphide into a solution of arsenic acid, heated the solution and filtered off the precipitate, and then by the addition of silver nitrate showed that both arsenious and arsenic acids were present in the filtrate. It was therefore accepted that reduction takes place and the reaction was represented thus ... 

Exercise 15-3 What type of infrared absorption bands due to hydroxyl groups would you expect for frans-cyclobutane-1,2-diol and butane-1,2-diol (a) in very dilute solution, (b) in moderately concentrated solution, and (c) as pure liquids Give your reasoning. 

When a very dilute cold aqueous solution of the 1 1-dichloride is treated with chloroplatinic acid, the chloroplatinate separates as a pale yellow microcrystalline powder, sintering at 190° C. and decomposing at 216° C. It is almost insoluble in water, but dissolves in chloroform or benzene. If the chloroplatinic add be added to a hot, moderately concentrated solution of the 1 1-dichloride, sparingly soluble orange bis-1 -chlorocycloselenipentane 1-chloroplatinate is precipitated. This decomposes at 160° C., is insoluble in organic solvents with the exception of alcohol, and has the constitution... 

In the following sections we discuss some aspects of solute-solvent interactions. This discussion is not a complete, current survey but rather an attempt to bring together some divergent experimental facets of water-solute interactions which often are not discussed by either theoreticians or experimentalists. For more detailed, general information see Refs. 18, 19, 20, and 73. The two essential points we wish to make are (1) even in moderately concentrated solutions, there is evidence for the persistence of structural elements of the type found in pure water and especially in dilute solutions (2) there is evidence for what appears to be discrete changes with concentration in the behavior of some aqueous solutions of both electrolytes and nonelectrolytes, and for nonelectrolytes this may be caused by the existence of discrete sites available to the solute molecules. Unfortunately, we shall be able to discuss only electrolyte-water interactions to any extent the often more interesting nonelectrolyte-water interactions will be discussed in a later paper. This is all the more... 

Artificial Sweetening Substances.—These are detected in a moderately concentrated solution of the substance by the methods given for liqueurs (see Spirits and Liqueurs). 

A peculiar method of desalting water is the osmionic demineralization developed by G. W. Murphy (702,103). In a multicell are circulated side by side a very concentrated salt solution, a moderately concentrated salt solution and a dilute salt solution to be desalted. The arrangement is now such that only Na+ and Cl- ions can move from the brine to the moderately concentrated salt solution, when simultaneously also Na+ and Cl- ions can move from the dilute salt solution to this moderately concentrated solution. In this manner the dilute solution is desalted. 

An absence of the Gibbs-Marangoni effect is the main reason why pure liquids do not foam. It is also interesting, in this respect, to observe that foams from moderately concentrated solutions of soaps, detergents, etc., tend to be less stable than those formed from more dilute solutions. With the more concentrated solutions, the increase in surface tension which results from local thinning is more rapidly nullified by diffusion of surfactant from the bulk solution. The opposition to fluctuations in film thickness by corresponding fluctuations in surface tension is, therefore, less effective. 

J. O. Park and G. C. Berry, Moderately concentrated solutions of polystyrene. III. Viscoelastic properties at the Flory theta temperature , Macromolecules, 22, 3022 (1989). 

These conclusions are in agreement with results reported by Janeschitz-Kriegl (1969), who measured the shear compliance JeR of highly concentrated to very dilute solutions of a series of polystyrenes with narrow molecular weight distributions. For the melt down to moderately concentrated solutions JeR appeared to be equal to 0.4, which is the value to be expected for free-draining solutions. In very dilute solutions JeR tended to decrease to the non-draining case, where /eR=0.205. 

We have made a number of assumptions in this calculation, the most notable being that the ionic solutions are ideal, in that there are no interactions (attractive or repulsive) between solute molecules. It is most unlikely that this is the case, especially in moderately concentrated solutions of ions. In order to correct for nonideality (interactions between solute molecules), we need to substitute the activities of solute molecules for their concentrations in all thermodynamic calculations. The activity (a) of a solute molecule is related to its concentration (C) by an activity coefficient (y). 

The viscosities of concentrated solutions of phosphoric acid are high those of moderately concentrated solutions are given below —... 

Neutral solutions of benzoates yield a salmon colored precipitate with ferric chloride TS. From moderately concentrated solutions of benzoate, 2 A sulfuric acid precipitates free benzoic acid, which is readily soluble in ether. 

Potassium compounds impart a violet color to a nonluminous flame if not masked by the presence of small quantities of sodium. In neutral, concentrated or moderately concentrated solutions of potassium salts, sodium bitartrate TS (10%) slowly produces a white, crystalline precipitate that is soluble in 6 N ammonium hydroxide and in solutions of alkali hydroxides or carbonates. The precipitation may be accelerated by stirring or mbbing the inside of the test tube with a glass rod or by the addition of a small amount of glacial acetic acid or alcohol. 

The complexes are very soluble in methanol, ethanol, butanol, methyl Cellosolve (2-methoxyethanol), and ethyl Cellosolve (2-ethoxyethanol), and to a fair degree, quite soluble in 1,2-dimethoxyethane and di- and triglyme. They are initially quite soluble in tetrahydrofuran, acetone, pyridine, nitro-methane, acetonitrile, dimethyl sulfoxide, and iV,A/-dimethyl-formamide, but usually precipitation of the nickel halide-solvent complex occurs if attempts are made to prepare moderately concentrated solutions in these solvents. They are only very slightly soluble, or are quite insoluble in dioxane, ethyl ether, hexane, dichloromethane, ethyl acetate, and methyl- and butyl-cellosolve acetate (2-methoxyethyl and 2-butoxyethyl acetate). 

Barium chloride solution white precipitate of barium thiosulphate, BaS203, from moderately concentrated solutions. 

Condensations of bis(o-mercapto)phenyl sulfide with paraformaldehyde or diiodomethane in moderately concentrated solutions gave dibenzo[//,g][l,3,6]trithiocine 56 in 28—49%> yields, accompanied with 6-10% yields of the product of 2 2 condensation, hexathiacyclohexadecine 131 (Scheme 33). Condensation with diiodomethane in diluted solution afforded trithiocine 56 as a sole product in 90% yield. Interestingly, when carbonyl or thiocarb-onyl diimidazoles were used as dielectrophile, formation of a 16-membered ring was predominant and the eight-membered product 132 was not observed <1999H(50)103>. 

Aminotetrazole on treatment with nitrous acid in dilute aqueous solution yields a diazonium salt which undergoes the usual coupling reactions.37 On treatment with alkali the solution becomes yellow and probably diazotetrazole is present. However, if the reaction is carried out in moderately concentrated solution, an explosive mixture is obtained The reviewer has had dramatic, if harmless, experience of this system. After one originally mild explosion had shattered the reaction vessel, the solution, now scattered about the room and the experimenter, produced small detonations for the next 4 hours The very formula of the compound explains its instability (64). 

In principle one can also obtain data on refractive-index differences by measuring the indices of solutions, but this method suffers from a number of problems. Even for moderately concentrated solutions, the absolute index differences are small, and it is difficult to be certain that they are not masked by effects of small variations in temperature or concentration. 

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