Solubility rules for inorganic compounds

TABLE 11.46 General Solubility Rules for Inorganic Compounds ... 

For most analyses, standard solutions are aqueous solutions containing several percent of a mineral acid such as HCl or nitric acid. When mixing different elements in acids, it is important to remember basic chemistry and solubility rules for inorganic compounds. The elements must be compatible with each other and soluble in the acid used so that no precipitation reactions occur. Such reactions would change the solution concentration of the elements involved in the reaction and make the standard useless. Combinations to be avoided are silver and HCl, barium and sulfuric acid, and similar... 

SOME SOLUBILITY RULES FOR INORGANIC SALTS IN WATER Compound Solubility ... 

Use the Handbook of Chemistry and Physics or other suitable reference to find solubility data for inorganic compounds. What are some qualitative rules that relate to solubilities ... 

As a general rule, organic compounds are usually more soluble in liquid ammonia than they are in water. Inorganic salts are usually more soluble in water unless the cation forms stable complexes with NH3. For example, AgCl is more soluble in liquid ammonia than it is in water because of the stability of Ag(NH3)2+. Because the basic species in liquid NH3 is NH2, reactions that involve strongly basic materials can frequently be carried out in liquid NH3 more readily than they can in water because NH2 is a stronger base than OH-. Some of the important physical properties of liquid NH3 are shown in Table 5.5. 

The test identifies the substance to be examined as a salt of potassium, K+. As with other alkali metals, potassium is exclusively found as the monovalent cation. Since almost all salts of potassium are water soluble and it is a very inert ion, as a rule these do not contribute to the characteristics of its salt. For this reason its function in the compounds enrolled in the pharmacopoeia is to be an indifferent counter-ion, both for simple inorganic anions but also for anionic active pharmaceutical ingredients. Reference to potassium is made in about twenty-five monographs. In about half of them test (b) is dictated in about one-quarter and in the last quarter both tests have to be performed. The anions in the organic salts are, with the exception of Acesulfame, carboxylic acids. Due to the high water solubility of potassium, sample preparation is in most cases just a simple dilution in water. 

Intermetallic compounds form a particular class in the inorganic chemistry. They present different behaviours large fields of solid solubility and simple stnjctures as in the brass alloys, but also in most cases fixed composition and complicated structures. Anyway, the formula of an intermetallic compound is not in principle a priori known, as it does not follow the normal rules of the valence. Some formulae, for example AB, AB2, A5B3, occur very frequently, but we have also exotic formulae as CoZn.13, Ca3 Sn2o, Sm.. Cd45. Therefore, the determination of the crystal structure must be preliminary to any other measurement or property investigation. 

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