Efflorescent compounds

Gopper(II) Sulfates. Copper(II) sulfate pentahydrate [7758-99-8] CuS04-5H20, occurs in nature as the blue triclinic crystalline mineral chalcanthite [13817-21 -5]. It is the most common commercial compound of copper. The pentahydrate slowly effloresces in low humidity or above 30.6°C. Above 88°C dehydration occurs rapidly. 

In recent years this simple picture has been completely transformed and it is now recognized that the alkali metals have a rich and extremely varied coordination chemistry which frequently transcends even that of the transition metals. The efflorescence is due to several factors such as the emerging molecular chemistry of lithium in particular, the imaginative use of bulky ligands, the burgeoning numbers of metal amides, alkoxides, enolates and organometallic compounds, and the exploitation of multidentate... 

Potassium Tetrathiocyanato-dipyridino-chromium, [Cr py2 (SCN)4]K.2H,0, is prepared by heating potassium ehromithiocyanate with anhydrous pyridine. The melt is reerystallised from a little wTater, and on cooling a stable red powder separates. The thiocyanato-groups are all within the complex, and the salt in solution therefore gives no coloration with ferric chloride. It is decomposed by chlorine in presence of cold water with formation of tetraquo-dipyridino-chromic chloride. If crystallised in the dry state from pyridine it forms transparent red crystals of the addition compound, [Cr py2(SCN)JK.4py, which quickly effloresce in air. 

The hexammino-salts are yellow or brownish compounds, easily crystallised and fairly stable. They withstand the action of boiling water for some time, and can therefore be crystallised from aqueous solution if crystallisation be carried out quickly. Acid solutions of the salts are very stable, but alkaline and neutral solutions are decomposed on heating. The salts are more soluble than the corresponding aquo-pentammino-salts, and their solutions are brownish yellow in colour. The hydrated salts effloresce in air and become opaque and reddish brown in colour. On heating they lose ammonia, leaving eobaltic oxide and a cobaltous salt. In cold solution they give no precipitate with sodium hydroxide, ammonium hydroxide, or alkali... 

When organic matter decays, say, in the soil of cattle yards and stables, ammonia and ammonium compounds are produced by the action of certain bacteria. If the soil be fairly dry, but not too dry, a white scum appears on the exposed surface. The scum is made up of small crystals of potassium nitrate and, after a time, if the soil be extracted with water and strained, the liquid, on evaporation, furnishes yellowish-brown crystals of crude nitre. The crude nitre can be purified by resolution and crystallization. The white efflorescence sometimes seen on the walls of stables, etc., is sometimes, though not always, due to the formation of nitrates in this way. 

A great many compounds exert a considerable vapor pressure because of thermal dissociation, with the production of one or more gaseous components. Such is the case with efflorescent hydrates. Other examples are the compounds (NH4)2S, WC16, PCU and many ammoniates, such as AgCl-3NH3. The extent of dissociation is... 

Nitric acid also occurs in combination with potassa or soda, in the form of an efflorescence in the soil, especially in tropical climates, as in some ports of India and Pern. The compound formed with soda constitutes the nitre, and with potassa, the saltpetre of commerce. 

The description of sources and methods of obtaining and purifying saltpeter is the earliest complete account of the preparation of that salt. It is apparently the basis of the somewhat condensed description in Agricola s De Be Metallica. Biringuccio says that saltpeter (sal nitro) is a compound of several substances, extracted by fire and water from dry earth containing manure, or from the efflorescence produced on new walls in damp places, or from the mouldy earth which is found in tombs or in unoccupied caves where rains cannot enter. After describing its physical properties and its explosive character, as in gunpowder, he continues ... 

Jilulc HNO, and concentrating the solution. The compound deliquesces in moist air and effloresces in dry air. The pink anhydrous cobaltous nitrate cannot he formed by dehydrating Ihe hexahydrate but by treating Ihe salt with nitrogen pentoxide gas (or in solution in concentrated HNOi). The salt is used mainly in the preparation of catalysts. 

Tetrapotassium hexakiscyanoferrate trihydrate [14459-95-1], K4[Fe(CN)J H20, is an efflorescent lemon yellow compound known as yellow prussiate of potash. The anhydrous material [13943-58-3] is obtained at 70°C. The compound is soluble in water and acetone, but insoluble in alcohol, ether, and ammonia. It is oxidized to hexakiscyanoferrate(3—) by oxygen in acidic solution, or by oxidants such as ozone, C, Br2, H202, or MnO. A large number of insoluble or slightly soluble mixed salts of the general formula K2MII[Fe(CN)(5] and KMIII[Fe(CN)(5] are known, eg, M11 = cobalt(II)... 

Sulfates. Iron(II) sulfate heptahydrate [7782-63-0], FeS04TH O, forms blue-green monoclinic crystals that are very soluble in water and somewhat soluble in alcohols. It is known by many other names including cupperas, green vitriol, and iron vitriol. The compound is efflorescent in dry air. In moist air, the compound oxidizes to yellow-brown basic iron(III) sulfate. Aqueous solutions tend to oxidize. The rate of oxidation increases with an increase in pH, temperature, and light. The compound loses three waters of hydration to form iron(II) sulfate tetrahydrate [20908-72-0], FeS04 TH O, at... 

The crystals effloresce slowly when exposed to air and are decomposed by carbon dioxide. Consequently, they must be kept sealed off from air. This compound is, moreover, very soluble in water. 

In the second column the behavior of the crystallized salt when it is exposed to the air of the laboratory is indicated s = stable, i.e. unchanged by exposure to atmosphere e = efflorescent d = deliquescent d, e = deliquescent or efflorescent, according as to whether the humidity is above or below the average C02 = absorbs carbon dioxide and falls to a white powder Ox - compound is oxidized, especially in presence of moisture Hyd = hydrolyzed, even by the water vapor of the air. 

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