Decahydrate, definition

More than 30 years ago, Scott, Obenhaus, and Wilson (135) suggested that for lithium chloride, a solute to solvent ratio of 1 10 corresponded to a definite composition, and they quoted earlier measurements (134) as indicating two distinct, definite values for the magnetic susceptibility of lithium chloride above and below the concentration, corresponding to a decahydrate in solution. Likewise, anomalies were also found in the density of such solutions. Scott, Obenhaus, and Wilson also quoted Hiittig and Keller (83) who found that the densities, refractive indices, and coefficient of extinction of lithium halide solutions showed discontinuous changes with concentration for molar ratios of water to solute of 6, 30, and 75. 

The only definite borate hydrates of cobalt are the CoO - 3B203 - 8H20 and CoO 3B203 10H2O compounds. The octahydrate is prepared by evaporation of acetic acid from cobalt acetate-boric acid mixtures, or by mixing aqueous solutions of cobalt chloride, borax, and boric acid (206). The 1 3 7.5 borate can form as a solid solution and, in the presence of 3% boric acid, affords the decahydrate (117). The crystal structure determination of this 1 3 10 compound shows it to possess the hexaborate ion (380). The IR spectra (402) and thermal decomposition (396) of these compounds have been determined. 

Ammoniates. Review what was said in Chapter II about water of crystallization and hydrates (pp 62-65). Two definite crystalline compounds of sodium carbonate and water are the monohydrate and the decahydrate. Both of these will dissolve in water, but both solutions are absolutely identical. Furthermore, either one or the other of these hydrates can be caused to crystallize from the solution by adjusting the temperature. 

Since, as has already been stated, each solid substance has its own solubility curve, there are three separate curves to be considered in the case of sodium sulphate and water. Where two curves cut, the solution must be saturated with respect to two solid phases at the point B, therefore, the point of intersection of the solubility curve of anhydrous sodium sulphate with that of the decahydrate, the solution must be saturated with respect to these two solid substances. But a system of two components existing in four phases, anhydrous salt—hydrated salt —solution— vapour, is invariant and this invariability will remain even if only three phases are present, provided that one of the factors, pressure, temperature, or concentration of components retains a constant value. This is the case when solubilities are determined in open vessels the pressure is then equal to atmospheric pressure. Under these circumstances, then, the system, anhydrous sodium sulphate — decahydrate—solution, will possess no degree of freedom, and can exist, therefore, only at one definite temperature and when the solution has a certain definite composition. The temperature of this point is 32 383°, or, in round figures, 32 4°, and the solution contains 33 20 per cent, of anhydrous salt. 

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. 

Decahydrate, powder, no definite melting range. Freely sol in watei slightly sol in boiling 95% ethanol practically insol in abs ethanol, acetone, chloroform. pH o( a 2% aq soln 6 to 8. Precipitated From aq solns by acids. 

Water is frequently bound to other chemical compounds. Water bound to a salt in a definite proportion is called water of hydration. An important example is sodium carbonate decahydrate Na2C03 IOH2O. This salt is used in detergents, as... 

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