Temperature dependence, solubility minimum

Solubility is a function of temperature because both P and y are temperature dependent. Usually y falls with increasing temperature thus solubility increases. This implies that the process of dissolution is endothermic. Exceptions are frequent and in some cases, such as benzene, there may be a solubility minimum as a function of the temperature at which the enthalpy of dissolution is zero. 

There is a minimum in the experimental temperature dependence of hydrogen solubility in the FeV-H alloy [28]. For this alloy the condition... 

We turn now to the temperature dependence of the cmc. Eqn (6.1) gives little indication of how the cmc should vary with temperature. The observed cmcs all have a minimum between 20-30°C, for sodium n-dodecyl, n-decyl and 2-decyl sulphates, and for n-dodecyl trimethylammonium bromide. While the temperature dependence of the term lyaojkT could be estimated from data on the surface tension of water and decreases with temperature, we have no information on the temperature dependence of the hydrophobic term g—g. However, evidenceon the solubilities and enthalpy of solution of the sequence ethane, propane, butane,... 

Salting out much depends on the pH and temperature of the solution. Proteins show minimum solubility around their isoelectric point (PI) in water and a little lower solubility in buffer solution, in other words, in the presence of salt. Regarding temperature, the solubility of proteins generally decreases at higher temperature in buffer solution with higher ionic strength. 

The temperature dependence of hydrophobicity is interesting and has helped in understanding the phenomenon. With an increase in temperature of the solution from 0 °C, the solubility of a hydrophobic solute first decreases, reaches a minimum around 25 °C, and then continues to increase up to 100. Thus, the hydrophobicity... 

It is a characteristic feature of ionic surfactant micelliza-tion that the CMC is, to a first approximation, independent of the temperature. The temperature-dependence of the CMC of sodium dodecyl sulfate (SDS), displayed in Figure 19.6, is a good illustration of this. The CMC varies in a non-monotonic way by ca. 10-20% over a wide range. The shallow minimum at around 25°C can be compared with a similar minimum in the solubility of hydrocarbons in water. Nonionic surfactants of the polyoxyethylene type deviate from this behaviour and show typically a monotonic, and much more pronounced, decrease in CMC with increasing temperature. As will be discussed briefly at the end of this chapter, this class of nonionics behaves differently from other surfactants with respect to temperature effects. 

Gas solubilities are generally strongly temperature-dependent, so much so that the logarithm of solubility (In Xg) versus inverse temperature (1 / T) yields a straight line. Intuitively, gas solubility should diminish as a function of the temperature, but experimental measurements have shown that a minimum in gas solubility at a certain temperature is a common behavior (Figure A8.1) [3]. 

The marked temperature dependence of borate solubility may be useful in certain oilfield chemical applications. It is also notable that water solubility varies with the ratio of min (the compound s molar content of M2O/B2O3) with solubility maxima corresponding approximately with the compounds disodium octaborate (min = 0.25) and sodium metaborate (min = 1.0) and with a minimum that corresponds with disodium tetraborate (borax) (m n = 0.5) [13,14]. 

Minimum In the temperature dependency of hydrocarbon solubility In water... 

Table 4.19 gives the Henry constants for a few common gaseous components. The chemical nature is also a dominant factor. The effect of temperature is moderate note that the solubility passes through a minimum that depends on the hydrocarbon in question and that it is around 100°C. 

Since the satiuation concentration is a function of pressme as well as temperature, the geothermometer temperature is dependent on pressmes. At 1000 bar, which is roughly equivalent to a depth below the seafloor of 1.6 km (750 bar) in a 2.5-km water depth (250 bar), the regression line intersects the solubility ciuwe of quartz at 345°C. Thus, the quartz geothermometer estimates a minimum temperature of 345°C for the undiluted hydrothermal fluid at the Galapagos vents. 

NOTE Calcium carbonate is in fact sparingly soluble (typically the solubility ofCaCOi is to the extent of 15 to 20 ppm depending on temperature and other factors). If a decrease in cooling water pH occurs and there is a resultant increase in CO2. in excess of the minimum necessary to establish equilibrium, this can, under certain conditions, resolublize some or all of the calcium carbonate scale. 

The dependence of the mutual solubility with water on the temperature cannot be described by a simple expression, since it is the result of opposing effects. Many solvents experience a shallow minimum in the solubility near room temperature, but this is by no means a universal behaviour. 

The dependence of the solubility on the temperature Sq (T) or S° (T) shows that these functions may have a minimum under the condition... 

The initial raw material should contain the minimum impurities and admixtures of sulphates, calcium and magnesium salts. A sodium chloride solution is applied in a saturated state potassium chloride solutions are generally unsaturated to prevent the danger of the pipes becomming clogged at an unexpected cooling of the solution as the solubility of this salt depends to a considerable degree upon the temperature. 

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