Solid-solution solubilities

Recently (Ruckenstein and Shulgin, 2003c), a method was suggested to calculate the activity coefficient of a poorly soluble solid in an ideal multicomponent solvent in terms of its activity coefficients at infinite dilution in some subsystems of the multicomponent solvent. The method, based on the fluctuation theory of solutions (Kirkwood and Buff, 1951), provided the following expression for the activity coefficient of a poorly soluble solid solute in an ideal multicomponent solvent ... 

Thermodynamic equilibrium measurements of solid-solution solubilities would be the ideal method for obtaining solid-solution excess-free-energies. Unfortunately, thermodynamic equilibrium states commonly can not be obtained in the laboratory, as solid-solution recrystallisation experiments have indicated (4). SSAS systems with highly soluble solid-solutions capable of rapid recrystallisation, such as the K(Cl,Br) - H O system, are a significant exception to this rule (Glynn and Reardon, Am. L Sci. in press). 

A water-soluble mixture may be in the form of a mixture of water-soluble solids or in the form of a liquid. The liquid mixtimes are frequently aqueous solutions. The prelirninary examination of a liquid mixture (see 1) will indicate whether a volatile solvent (i.e., removable on a boiling water bath) is present. If a volatile solvent is present, distil 20 g. of the mixtime from a water bath until no more hquid passes over set aside the volatile solvent for identification. Dissolve the residue (B) in water as detailed below for a mixture of solids. 

In report separately discuss the peculiarities of determination of the anion composition of the solid solutions, that conditioned by ability of diphosphate anion to destruction in water solutions. In given concrete case by most acceptable method of control of the diphosphate anion in the hydrated solid solutions is a traditional method of the quantitative chromatography on the paper. Methodical ways which providing of minimum destruction of the diphosphate anion in the time of preparation of the model to analysis (translation in soluble condition) and during quantitative determination of the P.,0, anion are considered. 

As you can see from the tables in Chapter 1, few metals are used in their pure state -they nearly always have other elements added to them which turn them into alloys and give them better mechanical properties. The alloying elements will always dissolve in the basic metal to form solid solutions, although the solubility can vary between <0.01% and 100% depending on the combinations of elements we choose. As examples, the iron in a carbon steel can only dissolve 0.007% carbon at room temperature the copper in brass can dissolve more than 30% zinc and the copper-nickel system - the basis of the monels and the cupronickels - has complete solid solubility. 

Fig. 10.5. TTT diagram for the precipitation of CuAh from the Al + 4 wt% Cu solid solution. Note that the equilibrium solubility of Cu in Al at room temperature is only 0.1 wt% (see Fig. 10.3). The quenched solution is therefore carrying 4/0.1 = 40 times as much Cu as it wants to.

The alloy aluminium-4 wt% copper forms the basis of the 2000 series (Duralumin, or Dural for short). It melts at about 650°C. At 500°C, solid A1 dissolves as much as 4 wt% of Cu completely. At 20°C its equilibrium solubility is only 0.1 wt% Cu. If the material is slowly cooled from 500°C to 20°C, 4 wt% - 0.1 wt% = 3.9 wt% copper separates out from the aluminium as large lumps of a new phase not pure copper, but of the compound CuAlj. If, instead, the material is quenched (cooled very rapidly, often by dropping it into cold water) from 500°C to 20°C, there is not time for the dissolved copper atoms to move together, by diffusion, to form CuAlj, and the alloy remains a solid solution. 

An intermediate compound A2B3 melts at 1230°C. It has a limited solid solubility for A, forming solid solution and no solid solubility for B. 

The solution was filtered and evaporated in vacuum over concentrated sulfuric acid. The sodium salt is then obtained as a creamy white water-soluble solid. Glycyrrhetinic acid is obtainable from licorice root. 

Platinum is unaffected by most organic compounds, although some compounds may catalytically decompose or become oxidised on a platinum surface at elevated temperatures, resulting in an etched appearance of the metal. Carbon and sulphur do not attack platinum at any temperature up to its melting point. Molten platinum may dissolve carbon, but the solubility of the latter in solid solution is virtually zero. 

Let x and x denote the mole fractions of the two sparingly soluble solids in their respective saturated solutions let y and y denote their mole ratios, m and ml their molalities, and a and a their activities on the molality scale. If the saturated solutions are sufficiently dilute, we may, with sufficient accuracy, neglect the differences between the four ratios x/x, y/yf, m/m, and a/a. We can express the difference between the cratic terms by means of any of these quantities, thus,... 

One way to establish equilibrium between a slightly soluble solid and its ions in solution is to stir the solid with water to form a saturated solution. As you might expect, the solubility of the solid, s, in moles per liter, is related to the solubility product constant, Ksp. In the case of barium sulfate dissolving in water we have... 

The less soluble solid precipitates first the more soluble solid stays in solution. 

A solid solution of starch in urea may also be employed. Reflux 1 g of soluble starch and 19 g of urea with xylene. At the boiling point of the organic solvent the urea melts with little decomposition, and the starch dissolves in the molten urea. Allow to cool, then remove the solid mass and powder it store the product in a stoppered bottle. A few milligrams of this solid added to an aqueous solution containing iodine then behaves like the usual starch indicator. 

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