Solubility maxima, definition

Gay-Lussac had determined the solubilities of several salts in water at different temperatures and plotted solubility curves. He recognised that the solubility is definite at a given temperature in presence of the solid salt (toujours en contact avec le sel). He noticed the break in the solubility curve of Glauber s salt (Na2S04,ioH20) and that this occurs at a maximum of solubility, but he did not explain this as due to the formation of a new solid phase (Na2S04). This was stated independently by Kopp and by Berzelius. The production of crystalline anhydrous sodium sulphate from hot solutions of Glauber s salt had, however, been described by Thomson in 1826. ... 

Solutions are mixtures, and therefore do not have definite compositions. For example, in a glass of water it is possible to dissolve 1 teaspoonful of sugar or 2 or 3 or more. However, for most solutions there is a limit to how much solute will dissolve in a given quantity of solvent at a given temperature. The maximum concentration of solute that will dissolve in contact with excess solute is called the solubility of the solute. Solubility depends on temperature. Most solids dissolve in liquids more at higher temperatures than at lower temperatures, while gases dissolve in cold liquids better than in hot liquids. 

Solutions are mixtures and therefore do not have definite compositions. For most solutions there is a limit to how much solute will dissolve in a given quantity of solvent at a given temperature. The maximum concentration of solute that will dissolve in contact with excess solute is called the solubility of the... 

The choice of 20 mN m" as a standard value of surface tension lowering for the definition of adsorption efficiency is convenient, but, as mentioned, somewhat arbitrary. When one discusses the effectiveness of adsorption, as defined as the maximum lowering of surface tension regardless of surfactant concentration, the value of o-min is determined only by the system itself and represents a more firmly fixed point of reference. The value of oinm for a given surfactant will be determined by one of two factors (1) the solubility limit or Krafft temperature (Tk) of the compound, or (2) the critical micelle concentration (cmc). In either case, the maximum amount of surfactant adsorbed is reached, for all practical purposes, at the maximum bulk concentration of free surfactant. 

The membrane process can be kinetically or thermodynamically controlled. Thermodynamic control exists if there is a limit set by the distribution coefficient or a reaction equilibrium constant which is approached asymptotically at a slow rate. The process will be kinetically controlled if it is far away from the thermodynamic limit or if this limit is removed. The removal of amaonia from an aqueous effluent by the liquid membrane process will be used as an example to illustrate the difference between the two definitions. On account of solubility of ammonia in the membrane phase the same distribution coefficient will apply at the two surfaces of the membrane phase. The internal phase thus cannot take up more ammonia than given by the distribution coefficient at the internal surface. In turn, the maximum amount of ammonia... 

Data obtained from typical CRH determinations uti-li2ing the method described above are shown in Hgurc 18.11. The data obtained for prilled urea are typical of relatively pure materials, in that the critical point is quite definite. There was no moisture absorption in 3 hours at 70% relative humidity, but there was continuous absorption at 75%. The data shown for the fertilizer grade diammonium phosphate, on the other hand, illustrate typical behavior of fertilizers that contain small amounts of soluble impurities. It is obvious that the CRH of the main constituent is between 70% and 75% for practical purposes, however, it would have to be recognized that exposed product would pick up some moisture at relative humidities between 60% and 70%. At 70% relative humidity, a maximum of 2% would be absorbed. For most diammonium phosphate products, this is insufficient to cause intergranule transfer of moisture thus, only the surface granules would be affected in a bulk... 

A quantitative definition of solubility is the maximum number of grams of a solute that will dissolve in a given volume of water at a particular temperature. Describe an experiment that would enable you to determine the solubility of a soluble compound. 

The results presented so far have been obtained with Combination 1 [4] of solubility and diffusivity laws (Table 10.2). Calculations have been made for Combinations 2 and 3 in order to determine the influence of the diffusivity and solubility parameters. Results show that the choice of the combination of solubility and diffusivity laws strongly influences the amount of hydrogen obtained at the interface. This is particularly the case for Combination 2, where the differences between base materials and overlay have been maximised. This is illustrated on Fig. 10.4 where the maximum hydrogen content obtained from Combinations 1 and 2 are compared. The relationship between maximum hydrogen contents calculated from Combination 1 and 2 is a linear one. This means that whatever the choice of diffusivity and solubility laws (in the range of variation considered), definitions of equivalent testing conditions for laboratory tests will be similar. 

Recall the definition of a saturated solution. It has the maximum number of grams of a solute that can be dissolved (solubility). 2. Use the solubility in g/L as a conversion factor to find the mass needed to prepare 298 mL of a saturated solution. ... 

---