Saturated and supersaturated solutions

Students will compare and contrast the physical properties of unsaturated, saturated, and supersaturated solutions. 

This equilibrium is stable in general, 214.—X84. Solutions. Saturation. Solubility curve, 216.—X85. For a hydrated salt two saturated solutions correspond to each temperature. The solubility curve has two branches, 216.—x86. Non-saturated and supersaturated solutions, 217.—X87. Heat of solutions in saturated solutions, 219.— x88. Displacement of equilibrium by variation of temperature, 219. 

Megrab et al. (1995) measured the uptake of estradiol into stratum corneum from saturated and supersaturated solutions in various propylene glycol-water vehicles. As propylene glycol content in saturated solutions increased, so did uptake of estradiol. As degree of supersaturation increased, so also did the uptake ratio. In addition, the flux of estradiol across the... 

The almost total absence of diffusivity data in concentrated, saturated, and supersaturated solutions makes the estimation of diffusivity difficult in many cases. In order to estimate the diffusivity at the desired conditions, the first step is to find out if any experimental data exists (even at infinite dilution) for the diffusivity of the solute in the solvent of interest. 

In saturated and supersaturated solutions one can observe deep capacitance depressions, which appear to correspond to the formation of polylayers rather than monolayers. The distinguishing feature here seems to be that no stationary capacitance can be reached [17]. 

In this chapter, you learned about solutions. A solution is a homogeneous mixture composed of a solvent and one or more solutes. Solutions may be unsaturated, saturated, or supersaturated. Solution concentration units include percentage, molarity, molality, and mole fraction. The solubility of solids in liquids normally increases with increasing temperature, but the reverse is true of gases dissolving in liquids. The solubility of gases in liquids increases with increasing pressure. 

Heat the test tube with its contents to obtain a transparent solution again, carefully cool it, and rub the inner wall of the test tube containing the solution with a glass rod. Explain the precipitation of crystals. Give definitions of saturated, unsaturated, and supersaturated solutions. 

Although gas evolution is usually endothermic in open systems, and seldom a problem on laboratory scale, industrial batch reactors combine relatively far smaller vents with lower rupture pressures. This can give dangers with even endothermic evolutions. Exothermic gas evolving reactions readily become uncontrollable. A further hazard is nucleation and heating of saturated and supersaturated gas solutions when crystallisation of products occurs this is the cause of many reactions jumping... 

As one progresses from unsaturated to saturated to supersaturated solutions, the number of solute particles increases and therefore the intensity increases. 

In the previous section, you read about saturated, unsaturated, and supersaturated solutions. These terms are all related to the amount of solute that is dissolved into a solvent. However, you probably also know that the temperature of a solvent affects the amount of solute that can dissolve in it. The degree to which the temperature affects dissolving is something specific to each substance, but for most solid solutes, an increase in temperature will lead to an increase... 

Crystals form in supersaturated solutions in which the solute concentration exceeds its solution solubility. Supersaturation is usually expressed as either of the ratios dc or (c — c )lc, where c is the concentration of solute before crystallization and is the solute equilibrium saturation concentration. Supersaturated solutions are thermodynamically metastable. Equilibrium can be restored by reducing the solute concentration through precipitation or formation of nuclei and subsequent crystal growth. The super saturation requirements for nucleation and... 

Figure 7.2. Solubility and saturation. A schematic solubility diagram showing concentration ranges versus pH for supersaturated, metastable, saturated, and undersaturated solutions. A supersaturated solution in the labile concentration range forms a precipitate spontaneously a metastable solution may form no precipitate over a relatively long period. Often an active form of the precipitate, usually a very fine crystalline solid phase with a disordered lattice, is formed from oversaturated solutions. Such an active precipitate may persist in metastable equilibrium with the solution it is more soluble than the stable solid phase and may slowly convert into the stable phase.

The solubility relations of sodium sulphate illustrate very clearly the importance of the solid phase for the definition of saturation and supersaturation. Since the solubility curve of the anhydrous salt has been followed backwards to a temperature of about 18 , it is readily seen, from Fig. 73, that at a temperature of, say, 20 , three different saturated solutions of sodium sulphate are possible, according as the anhydrous salt, the heptahydrate or the decahydrate, is present as the solid phase. Two of these solutions, however, would be metastable and supersaturated with respect to the decahydrate. 

It crystallizeB with 7 Aq. from saturated or supersaturated solutions at 5 (41 F.) or, more usually, with 10 Aq. As usually met with it is in large, colorless, oblique rhombic prisms with 10 Aq which effloresce in air and gradually lose all their Aq. It fuses at 33 (91. 4 F.) in its Aq, which it gr uaUy loses. If fused at 33 (91. 4 F.) and allowed to cool, it remuns liquid in supersaturated solution, firom which it is deposited, the entire mass becoming solid, on contact with a small particle of solid matter. It dissolves in Hd with considerable diminution of temperature. 

Distinguish among saturated, unsaturated, and supersaturated solutions and explain the equilibrium nature of a saturated solution ( 13.3) (EPS 13.29, 13.35)... 

Figure 1.26 Diffusion coefficients in aqueous KCl solutions at 25 °C (solution age = 24 h) in the metastable region, (Reproduced from Y.C. Chang and A.S. Myerson (1985), The Diffusivity of Potassium Chloride and Sodium Chloride in Concentrated, Saturated, and Supersaturated Aqueous Solutions, AIChE 7. 31, pp. 890 894. Used by permission of the American Institute of Chemical Engineers. 1985 AIChE.)...

In the author s experience, however, conductivity measurements are of limited use in crystallization work because of the unreliability of measurement in near-saturated or supersaturated solutions. The temperature dependence of electrical conductivity usually demands a very high precision of temperature control. Torgesen and Horton (1963) successfully operated conductance cells for the control of ADP crystallization, but they had to control the temperature to 0.002 °C. 

We begin by examining different types of solutions that can be formed from the three states of matter solid, liquid, and gas. We also characterize a solution by the amount of solute present as unsaturated, saturated, and supersaturated. (12.1)... 

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