Solubility Changes with Temperature

If A is a gas at ambient temperature and pressure, AsoiVH° can be determined experimentally by calorimetric methods or from measurements of the solubility change with temperature [42-44], When A is a liquid or a solid, its solvation enthalpy in a given solvent is usually calculated from its standard solution enthalpy (Asin//°) and its standard vaporization or sublimation enthalpy ... 

It is instructive to compare the thermochemical values with those obtained by the same authors when they assumed the ideal gas model (i.c.,/co = pco) and neglected the CO solubility change with temperature ArH%12 = 45.5 kJ mol-1 and ATS 72 = 267 J K-1 mol-1. 

Solubility of solids in liquids V I is usually given in units of grams of solute per 100 mL of solvent. Because solubility changes with temperature, the temperature is also specified (usually 20°C room temperature). 

The fact that solubility changes with temperature and that some substances become more soluble with increasing temperature is the key to forming supersaturated solutions. A supersaturated solution contains more dissolved solute than a saturated solution at the same temperature. To make a supersaturated solution, a saturated solution is formed at a high temperature and then cooled slowly. The slow cooling allows the excess solute to remain dissolved in solution at the lower temperature, as shown in Figure 14.16. 

We have studied oxide solubilities in molten CsCl-KCl-NaCl at 600 and 700"C in order to estimate oxide solubility changes with temperature. Oxide solubilities were lower than those predicted by Shreder s equation but estimations of their thermal changes usually were in a good agreement with those calculated from Shreder s equation. Oxides solubilities (in molar fractions) in KCl-NaCl and CsCl-KCl-NaCI have been found to be close at the same temperature. 

Graph solubility as a function of temperature and observe how the solubility changes with changing temperature. 

FIGURE 12.8 A graph showing how the solubility of a substance (in a hypothetical solvent) can change with temperature. 

In the monotropic case the relative solubility of the two polymorphs does not change with temperature if Form I is the most stable and least soluble at low temperatures then it will also be the same at all other temperatures, Figure 3. An example of this behavior is the Cimetidine Form A and B relationship presented in the case study of section 6. 

Explain qualitatively how the aqueous solubility of a (a) liquid, (b) solid, and (c) gaseous compound changes with temperature. Which thermodynamic quantity(ies) do you need to know for quantifying this temperature dependence ... 

The liquid crystalline regions obey the general rules for the liquid phases, but only where the hydrocarbon content is high. Along the water-emulsifier axis the changes with temperature are small in the PIT range this indicates that the structure of the liquid crystalline phase depends mainly on short range emulsifier-water interactions, which limits the solubility of water into the emulsifier. 

Reference electrode potentials change with temperature. Both electrochemical reactions (Nernstian thermodynamics) and chemical solubilities, e.g. of the inner reference electrode solution, are affected. Accordingly, the temperature coefficient, dE/dT (mV °C4), varies from one type of reference electrode to another. To minimise errors in potential readings the coefficient should be low and at least known. Examples of temperature coefficients are given in Table 2.2. 

As the solubility of a solute changes with temperature, and as the magnitude of the change in the two solvents may not be the same, the distribution coefficient (K) is found to vary with change in temperature. 

The Change in Apparent Calcium Carbonate Solubility Constants with Temperature (After Horse et al. (35))... 

An elegant confirmation of this conclusion is to be found in the change of solubility of slightly soluble electrolytes with temperature. For barium sulphate, e. g., the equilibrium between soluble and insoluble salt is expressible by... 

In addition, the solubility of calcium sulfate changes with temperature, going through a maximum at 35 °C and then diminishing drastically with increasing temperature as shown in Figure 31. 

The recrystallization technique is also effective for sparingly soluble salts e.g. KCIO4, when the solubility of the salt greatly changes with temperature. However, highly soluble salts such as KHCO3 caimot be effectively purified by reciystallization. 

Figure 13.20 shows how the solubilities of six different solutes change with temperature. 

The solubility of ammonium sulfate [(NH4)2 SOJ changes with temperature. The amount of (NH4)2 S04 needed to saturate 1,000 mL of H20 at 4° C is about 707 g. The saturated ammonium sulfate solution is prepared at room temperature by adding the solid salt to the desired volume of H20 with continuous stirring until some does not dissolve. Continue the stirring overnight. Adjust the pH to 7.4 with... 

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