Transition curve solubility curves

The equation shows that the solubility curve must be continuous all breaks indicate that the solid phase in contact with the saturated solution has altered in character, and we really have to do with two distinct solubility curves meeting at an angle. This occurs, for example, with Glauber s salt at 32° 6, for this is the transition temperature for the reaction... 

The curve below 32° 6 is the solubility curve of Na2S04.10H20 that above 32° 6 is the solubility curve of Na2S04. The idea that such breaks correspond with changes of hydration in the solution is quite unfounded, because all the properties of the homogeneous solution pass continuously through the transition temperature. 

Second, x-ray diffraction will, directly, give spacings in the crystal and reveal differences between samples. Finally, solubility curves can be carried out, and if a nick in the solubility curve is found (Fig. 9), this is a transition temperature. If no nick is found, there is no transition temperature, but if the dissolution curves are as shown in Fig. 5, there is polymorphism, and it may... 

Figure 6.3a shows the plot of log S versus pH of an ampholyte (ciprofloxacin, pKa values 8.62 and 6.16, log So — 3.72 [pION]). In Figs. 6.1b, 6.2b, and 6.3b are the log-log speciation profiles, analogous to those shown in Figs. 4.2b, 4.3b, and 4.4b. Note the discontinuities shown for the solubility speciation curves. These are the transition points between a solution containing some precipitate and a solution where the sample is completely dissolved. These log-log solubility curves are important components of the absorption model described in Section 2.1 and illustrated in Fig. 2.2. 

In the enantiotropic case the relative solubility and stability changes at a specific transition temperature where the two solubility curves cross. A given polymorph may be more soluble (less stable) above the transition point, but less soluble below and vice versa, Figure 4. An example of this relationship is the Form C and A or B relationships for Cimetidine in the case study. 

A plot of the ideal solubility curves can be used to identify the transition temperatures for the enantiotropic relationships. Form C is the most stable polymorph at high temperature, with a transition to Form B at 20 °C. The Form C to A transition occurs at 11 °C. 

In Fig. 42, let the curves SA and SB respectively denote the solubilities of an anhydrous salt and one of its hydrates associated with n mols. of water. Let T be the transition temp, where the vap. press, of a mixture of the two solids is equal to the vap. press, of their common sat. aq. soln. If a foreign solute be added to the, soln., the vap. press, is reduced, the transition temp, in the new soln. will be reduced to T, and the solubility curves of the anhydride and its hydrate will cross at T just as they cross at T when the pure solvent is used. Since the transition temp. T is lower than T, it will be necessary for the solubility of at least one of the two solids to be changed by the presence of the foreign substance. In that case it can be shown that (1) the solubility of the anhydride SA which forms a hydrate in soln. will be changed to SA (2) the solubility SB of the hydrate will likewise be increased to S (3) when a number of hydrates are formed in aq. soln., the solubility of the hydrate which has the greatest proportion of water will be increased and (4) when a number of hydrates are formed in aq. soln., the solubility of the hydrate, which has less water than the hydrate in the solid phase, will be increased, and, conversely, the solubility of those hydrates with more water than is present in the solid phase, will be diminished. 

The transition temperature of dodecahydrate /3-disodium hydrophosphate, stable at ordinary temp., into dodecahydrated d-disodium hydrophosphate, is 29-6°, and this is marked by a well-defined break in the solubility curve. 

Since the Zimm-Bragg parameters o and s of the naturally occurring amino acids (In water) cannot be obtained from studies of the helix-coil transition in homopolymers, because of experimental difficulties, a technique Is developed to circumvent these problems. It involves the study of the thermally induced transition curves for random copolymers of "guest amino acid residues in a water-soluble host" po y(amino acid). The data may be interpreted with the aid of suitable theories for the helix-coil transition in random copolymers to obtain a and s for the "guest" residues. It is shown in this paper that, for the usual ranges of parameters found for polylamino acids), one of the two lowest order approximations (corresponding to earlier treatments by Lifson and Allegra) is completely adequate. In essence, the low-order approximations hoid if o and s for the two constituents of the copolymer do not differ appreciably from each other. 

The anhydrous salt is obtained1 by heating the crystals to 120° C, If crystallisation takes place at the ordinary temperature, the dodeca-hydrate, Na2HAs04.12H20, is obtained while if the crystals are formed above 36° C. the heptahydrate, Na2HAs04.7H20, is produced. The transition point determined from the solubility curve of sodium monohydrogen arsenate in water 2 is at 22° C. 

Frthe SWJhHydmzineieSu°l- ammonium sulphate. The solubility curve, Fig. 53, phates. consists of two branches, intersecting at the transition... 

H3P04.H20 B is the melting point of this hydrate (29-35°) BC, the effect of phosphoric acid on the m.p. of the hemihydrate CD, the solubility curve of 10H3P04.H20 and C is the eutectic point (23-5°) of the two hydrates D is the transition point (26-2°) DE is the solubility curve of orthophosphoric acid and E is the melting point (42-30°) of orthophosphoric acid. W. H. Ross and R. M. Jones observed no break in the curve at D, and were unable to confirm the existence of the hydrate, 10H3P04.H20. J. Kendall and co-workers studied the hydrate formation with this and related acids. 

Mevcrhoffcr1 has plotted the solubility-curve (fig. G). The transition-temperature of the dihydrate into the anhydrous salt 3 (D) is 50-G71° C., and that of the pentahydrate into the dihydrate (C) is —24° C. 

The solubility-curve (fig. 7) is in conformity with the existence of a pentahydrate, the transition-point to the dihydrate 5 (D) being —13-5° C.,... 

In systems as described above, the rate of cooling must be significantly faster than the rate of nucleation in order for a glass to be formed. Effectively, the system must be cooled rapidly through the crystallization zone of the state diagram bounded by the solubility curve and the glass transition curve. Systems that crystallize more rapidly than they can be cooled will not form glasses. 

Figure 12-5. Intersecting solubility curves (dependence of the logarithm of the saturation concentration on the inverse temperature) indicate an enantiotropic nature of the polymorps, while parallel curves are indicative for monotropic polymorphs. The intercept for enantiotrops corresponds to the transition temperature.

Two very good illustrations of Meyerhoffer s law, according to which, at a transition point, a sharp bend occurs in the solubility curve for the salt suffering transformation, but not for that which remains unchanged ... 

Change other than solvation may occur in the stable solid phase. Thus rhombic sulfur (Chap. 17) is less soluble in suitable solvents than is monoclinic sulfur at temperatures below 95.5° C, the transition temperature between the two forms above this temperature the monoclinic form is the less soluble. The principles of thermodynamics require that the temperature at which the solubility curves of the two forms cross be the same for all solvents, and be also the temperature at which the vapor pressure curves intersect. 

The point E, intersection of the solubility curves of MgClj SHsOa and MgCl GH O this is a transition-paint for which... 

It is probable that in the neighborhood of 260 theie trould be found the intersection of the solubility curves of CaClj-H O and of CaCl, which would be a new transition-point. 

BIVARIANT SYSTEMS. TRANSITION AND EUTEXIA. 259 solubility curve of IGa this is a eutectic point for which... 

SOS. Common point to the solubility curves of two hydrates. Three cases to distinguish, page 240.—203. Transition point, 241.—... 

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