Solutes dissolution

Cellular automata simulations of the dissolution process have been described.42 The solute molecules, S, started in a solid block of cells at the center of the grid. They are endowed with rules PB(S), /(S), PB(WS), and /(WS). The attributes recorded from the dynamics were the /o(S), fraction of solutes unbound to other solute molecules, plus the average number of solute-solute joined faces, T(S), and the average distance that solute molecules have traveled from the center of the block at some specific iteration, D(S). The /o(S) values were interpreted to represent the extent of dissolution of the solute. The decrease in the T(S) values characterize the extent of disruption of the solute block, whereas the D(S) values quantify the extent of diffusion of solutes into the surrounding water. 

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A liquid solution may be separated into its constituents by crystallising out either pure solvent or pure solute, the latter process occurring only with saturated solutions. (At one special temperature, called the cryohydric temperature, both solvent and solute crystallise out side by side in unchanging proportions.) We now consider what happens when a small quantity of solute is separated from or taken up by the saturated solution by reversible processes. Let the saturated solution, with excess of solute, be placed in a cylinder closed below by a semipermeable septum, and the w7hole immersed in pure solvent. The system is in equilibrium if a pressure P, equal to the osmotic pressure of the saturated solution when the free surface of the pure solvent is under atmospheric pressure, is applied to the solution. Dissolution or precipitation of solute can now be brought about by an infinitesimal decrease or increase of the external pressure, and the processes are therefore reversible. If the infinitesimal pressure difference is maintained, and the process conducted so slowly that all changes are isothermal, the heat absorbed when a mol of solute passes into a solution kept always infinitely... 

The solubility of any solid can be either increased or decreased by the addition of an electrolyte to the solvent, a phenomenon known as the salt effect. Salting-out describes the situation in which the solubility of the solid is decreased by the salt effect, whereas salting-in is the term used when the solubility is increased. Salting-out takes place when the added electrolyte sufficiently modifies the water structure so that the amount of water available for solute dissolution is effectively reduced, and it is a procedure convenient for the isolation of highly soluble substances. 

When we speak of the dissolution of an estate, we are applying the common definition and we know that the estate will be broken up into parts. In chemistry, when we discuss the ease of solute dissolution, we are implying a full range of chemical and physical processes that take place when a solute dissolves. 

Fig. 9-14. Dissolution rate of a magnetite electrode observed as a function of electrode potential in sulAuic add solution dissolution rate Vnhe = volt referred to the...

Concentration Polarization As a reactant is consumed at the electrode by electrochemical reaction, there is a loss of potential due to the inability of the surrounding material to maintain the initial concentration of the bulk fluid. That is, a concentration gradient is formed. Several processes may contribute to concentration polarization slow diffusion in the gas phase in the electrode pores, solution/dissolution of reactants/products into/out of the electrolyte, or diffusion of reactants/products through the electrolyte to/from the electrochemical reaction site. At practical current densities, slow transport of reactants/products to/from the electrochemical reaction site is a major contributor to concentration polarization ... 

More complex forms of activity term rate laws involve various ions and complexes in solution. Dissolution and precipitation phenomena are in this approach regarded as a summation of individual reactions taking place at the surface of the solid. The net absolute rate is obtained as a summation of individual terms /, each with its specific rate constant k and activity product (Delany et al., 1986) ... 

Barium carbonate decomposes to barium oxide and carbon dioxide when heated at 1,300°C. In the presence of carbon, decomposition occurs at lower temperatures. Barium carbonate dissolves in dilute HCl and HNO3 liberating CO2. Similar reaction occurs in acetic acid. The solid salts, chloride, nitrate and acetate that are water soluble may be obtained by evaporation of the solution. Dissolution in HF, followed by evaporation to dryness, and then heating to red heat, yields barium fluoride. 

The red oxide is the acid anhydride of two acids, namely, chromic acid, H2Cr04 or Cr02(OH)2 and the dichromic acid H2Cr207. Both the chromic and dichromic acids exist only in the aqueous solution and have not been isolated from the solution. Dissolution of CrOs in water produces H+ ion along with dichromate ion, Cy20i as follows ... 

Components of the sample are retained in the column for different lengths of time due to adsorption-desorption, solution-dissolution, chemical affinity, size exclusion, and other mechanisms of varying nature. Various components are continually washed from one part of the stationary phase and recaptured by another by the moving phase. Different components elute in groups from the column with respect to time from injection. Dispersion in the system causes the bands of components to emerge with... 

Figure 13.5. Transport vs surface controlled dissolution. Schematic representation of concentration in solution, C, as a function of distance from the surface of the dissolving mineral. In the lower part of the figure, the change in concentration (e.g., in a batch dissolution experiment) is given as a function of time, (a) Transport controlled dissolution. The concentration immediately adjacent to the mineral reflects the solubility equilibrium. Dissolution is then limited by the rate at which dissolved dissolution products are transported (diffusion, advection) to the bulk of the solution. Faster dissolution results from increased flow velocities or increased stirring. The supply of a reactant to the surface may also control the dissolution rate, (b) Pure surface controlled dissolution results when detachment from the mineral surface via surface reactions is so slow that concentrations adjacent to the surface build up to values essentially the same as in the surrounding bulk solution. Dissolution is not affected by increased flow velocities or stirring. A situation, intermediate between (a) and (b)—a mixed transport-surface reaction controlled kinetics—may develop.

One important particle property affected by total surface area is solute dissolution, i.e., drug release rate. The drug release rate from a solid as described by the Noyes-Whitney equation is ... 

The maximum equilibrium solubility of a drug in a given medium is of practical pharmaceutical interest because it dictates the rate of solution (dissolution) of the drug (the rate at which the dmg dissolves from the solid state). The higher the solubility, the more rapid is the rate of solution when no chemical reaction is involved. 

Chemical etching is a process for removal of silicon dioxide films through dissolution in solutions. Dissolution of silicon oxides, in the context of this book, is related to the anodic behavior of silicon electrodes. However, the dissolution of anodic oxides is not well studied. In contrast, there is a wealth of information on the dissolution of other types of oxides. Much of this information must also be applicable, at least the qualitative and mechanistic nature, to that of anodic oxides. Also, because oxides of different types are commonly used in device fabrication, compiling the etch rate data of these oxides and those of silicon (presented in Chapter 7) in the same volume would be useful in practice. Additionally, because silica-water interaction, which has been extensively investigated in the geological field, is fundamental to the etching of silicon oxides, some of the results from the investigations on the dissolution of rocks and sands are also included. 

But we must leave these more general descriptions of our Secret Fire, and lead up to the operation or practice, and it will therefore be well to note the different functions that the fire performs in the Work. It has not idly been said that the gold must be tried seven times in the fire, nor are we to imagine that the Solutions, Dissolutions, Putrefactions, Calcinations, Sublimations, Decensions and Coagulations mentioned, are but reiterations of an identical process. Exact details of them are, as we know only too well, not... 

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