Differential crystalline hydrates

The heat absorbed upon dissolution of salts with univalent ions, not capable of hydrate formation, will increase according as the ionic radii of the ions become greater, since the energy of hydration decreases in the same sense Upon dissolution of KI and NaCl more heat per gram equivalent is absorbed in the former case. Sometimes the differential heat of dissolution of the anhydrous salt is positive in concentrated solutions and becomes negative upon further dilution. This will occur if the salt forms a crystalline hydrate, which then dissolves with absorption of heat... 

The mineralogical, structural, physical, and thermodynamic properties of the various crystalline alumiaa hydrates are Hsted ia Tables 1, 2, and 3, respectively. X-ray diffraction methods are commonly used to differentiate between materials. Density, refractive iadex, tga, and dta measurements may also be used. 

Other approaches use Laser-Raman spectra to differentiate five conformational states of lactose, including a-lactose monohydrate, /3-lactose, and lactose glass (Susi and Ard 1974). Differential thermal analysis has also been used to measure the concentration of crystalline lactose, especially a-lactose hydrate (Ross 1978B). The specialized equipment required by these procedures may limit their use. 

A study of the relaxational transitions and related heat capacity anomalies for galactose and fructose has been described which employs calorimetric methods. The kinetics of solution oxidation of L-ascorbic acid have been studied using an isothermal microcalorimeter. Differential scanning calorimetry (DSC) has been used to measure solid state co-crystallization of sugar alcohols (xylitol, o-sorbitol and D-mannitol), and the thermal behaviour of anticoagulant heparins. Thermal measurements indicate a role for the structural transition from hydrated P-CD to dehydrated P-CD. Calorimetry was used to establish thermodynamic parameters for (1 1) complexation equilibrium of citric acid and P-CD in water. Several thermal techniques were used to study the decomposition of p-CD inclusion complexes of ferrocene and derivatives. DSC and derivative thermogravimetric measurements have been reported for crystalline cytidine and deoxycytidine. Heats of formation have been determined for a-D-glucose esters and compared with semiempirical quantum mechanical calculations. ... 

Acetal is available as a homopolymer and a copolymer. Both types burn with a blue flame and give off a toxic formaldehyde odor. They are both crystalline with a specific gravity of 1.41. The homopolymer can be distinguished from the copolymer by a Fisher-Johns melting-point test. The copolymer acetal has a lower melting point than the homopolymer. Both types are soluble in hexafluoroacetone sesqui-hydrate. However, owing to the extreme toxicity of this solvent, it is rarely used for identification purposes. A differential thermal analysis (DTA) can also be used to distinguish a homopolymer from a copolymer. 

X-ray diffraction furnishes a rapid, accurate method for identifying crystalline phases present in a material. Sometimes, it is the only method available for determining which of the possible polymorphic forms of a substance are present—for example, carbon in graphite or diamond. Differentiating among various oxides, such as FeO, FcjOj, and Fc304 or between materials present in such mixtures as KBr -i- NaCl, KCl + NaBr, or all four, is easily accomplished with X-ray diffraction, whereas chemical analysis indicates only the ions present, and not the actual state of combination. The presence of various hydrates is another possibility. 

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