Temperature vs. solubility

Fig. 1. R,i (zt)-Malic acid solubility in water, showing maximum solubilities vs temperature (4).

The curve shown in Fig. 6 for sodium dodecyl sulfate is characteristic of ionic surfactants, which present a discontinuous and sharp increase of solubility at a particular temperature [80]. This temperature is known as the Krafft temperature. The Krafft temperature is defined by ISO as the temperature [in practice, a narrow range of temperatures] at which the solubility of ionic surface active agents rises sharply. At this temperature the solubility becomes equal to the critical micelle concentration (cmc). The curve of solubility vs. temperature intersects with the curve of the CMC vs. temperature at the Krafft temperature. 

Fig. 13. Quartz ai>d amorphous silica solubility vs. temperature along the vapour saturation curve. The dashed lines show the silica concentration in water initially in equilibrium with quartz during adiabatic boiling to 100 C and subsequent cooling. The increase in aqueous silica concentrations during boiling is the consequence of steam formation. Amorphous silica saturation (shown by the dots) is attained at 188 C in the case of the 300 C aquifer water, but at 94 C in the case of the 200 C aquircr water. It was assumed that the pH of the water is not raised sufficiently during boiling to cause significant ionization of the aqueous silica. If some ionization had occurred, amorphous silica saturation would be reached at lower temperatures than those indicated in Fig. 13.

Bertram (1989) showed, in dissolution studies of magnesian calcites, that their solubilities decrease with increasing temperature. This trend and its relationship to solubility vs. temperature trends for calcite and aragonite are discussed in Chapter 7. 

Figure 1. Solubility vs. temperature and log solubility vs. reciprocal temperature plots for MgDS ( ) and CaDS (O). Data from Ref. 10 included...

These equations and correlation coefficients were obtained by fitting solubility vs. temperature data to a polynomial regression (2° or 3°) program supplied with a Hewlett Packard 9830A Calculator. 

The solubility of over 300 common inorganic compounds in water is tabulated here as a function of temperature. Solubility is defined as the concentration of the compound in a solution that is in equilibrium with a solid phase at the specified temperature. In this table the solid phase is generally the most stable crystalline phase at the temperature in question. An asterisk on solubility values in adjacent columns indicates that the solid phase changes between those two temperatures (usually from one hydrated phase to another or from a hydrate to the anhydrous solid). In such cases the slope of the solubility vs. temperature curve may show a discontinuity. 

Figure 2.30 Various salts solubility vs. temperature (Macioszczyk, 1987).

Figure 2.45 Quartz and amorphous silica solubility vs. temperature (Krauskopf and Bird D. K., 1995).

Hayduk and Laudie (14) observed that all gases solubilities in a given solvent have a common value as the solvent critical temperature is approached. By extrapolating bilogarithmic curves of gas solubilities vs temperature to the solvent critical temperature, they determined reference solubilities in a number of polar and non-polar solvents. Beutier and Renon (18) confirmed the previous observations of Hayduk and Laudie (14) and they derived from thermodynamic considerations an exact value of the reference solubi1ity. 

In Experiments 3A and 3B, and in most of the experiments in this textbook, you are told what solvent to use for the crystallization procedure. Some of the factors involved in selecting a crystallization solvent for sulfanilamide are discussed in Technique 11, Section 11.5. The most important consideration is the shape of the solubility curve for the solubility vs. temperature data. As can be seen in Technique 11, Figure 11.2, the solubility curve for sulfanilamide in 95% ethyl alcohol indicates that ethyl alcohol is an ideal solvent for crystallizing sulfanilamide. 

Find a solvent with a steep solubility-vs.-temperature characteristic (done by trial and error using small ammmts of material or by consulhng a handbook). 

Listed below are solubility-vs.-temperature data for an organic substance A dissolved in water. 

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