Crystalline pentahydrates

This substance is familiar as the blue crystalline pentahydrate CUSO4.5H2O. In this crystal, each Cu ion is surrounded by four water molecules at the corners of a square, while the fifth water molecule is held by hydrogen bonds (see Figure 13.8). 

Sodium thiosulfate, either the anhydrous salt, Na2S202, or the crystalline pentahydrate, is commonly referred to as hypo or crystal hypo. When a concentrated sodium thiosulfate solution (50—60 wt %) is cooled to <48° C, the pentahydrate, containing 63.7% Na2S202, crystallines in monoclinic transparent prisms as shown in the equiUbrium phase diagram (Fig. 1). The monohydrate [55755-19-6] and the heptahydrate [36989-91-0] are also known. 

Heat of solution at infinite dilution (25°C) 52kJ/mol (crystalline pentahydrate) -38kJ/mol (amorphous) ... 

Borax Na2B407.10 H2O is the most significant borate it has a density of 1.715 g/cm. Careful dehydration yields a pentahydrate heating otherwise results in dehydration and produces a mixture of amorphous borate with crystalline pentahydrate containing 3.4—1.1 molecules of... 

Although 16 different crystalline modifications have been identified (24,25), the a-pentahydrate is the stable form below 48°C. Solutions of sodium thiosulfate in the absence of seed crystals can be easily supercooled below their normal crystallisation temperatures. The dotted line extension of the dihydrate phase in Figure 1 is an indication that, if supercooling takes place below this line, solutions normally giving the pentahydrate may form the dihydrate [36989-90-9] s1ste2id. 

Stannic Chloride Pentahydrate. Stannic chloride pentahydrate [10026-06-9] is a white, crystalline, deHquescent soHd that is soluble in water or methanol and stable at 19—56°C. It is used in place of the anhydrous chloride where anhydrous conditions are not mandatory. It is easier to handle than the fuming anhydrous Hquid form. The pentahydrate is prepared by dissolving stannic chloride in hot water, thereby forming the pentahydrate at a temperature above the melting point and crystallizing by cooling. The cake is broken into small lumps for packaging. 

Crystalline sodium pentaborate pentahydrate is stable in the atmosphere. When heated in vacuum, it is stable to 75°C however, above 75°C, four of its five H2O molecules are lost (73). 

Hypobromites, the salts of hypobromous acid, do not keep well because they gradually disproportionate to bromide and bromate. Solutions are best prepared as needed from bromine and alkafl with cooling. Because disproportionation is catalyzed by cobalt, nickel, and copper (70), these impurities should be avoided. SoHd alkaline earth hypobromites, or more properly, bromide hypobromites such as calcium bromide hypobromite [67530-61 CaBr(OBr), have been known for many years, but the pure crystalline hydrates sodium hypobromite pentahydrate [13824-96-9] NaOBr 5H20, and potassium hypobromite tribydrate [13824-97-0], KOBr 3H20, were not described until 1952 (71). Hypobromites are strong bleaching agents, similar to hypochlorites. 

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. 

Hydrates are compounds that incorporate water molecules in their crystalline structures. The ratio of moles of water to one mole of the compound is a small whole number. For example, in the hydrated compound copper(ll) sulfate pentahydrate (CuS04,5H20), the ratio is 5 1. The ratio of moles of water to one mole of a hydrate can be determined experimentally by heating the hydrate to remove water. 

Sodium pentahydrate is a colorless, odorless, crystalline solid density 1.69 g/cm3 decomposes around 50°C effloresces in dry air above 33°C very soluble in water and oil of turpentine insoluble in ethanol. 

The pentahydrate is a yellowish-white crystalline solid or small, fused lumps faint odor of HCl density 2.04 g/cm decmposes at 56°C very soluble in water soluble in ethanol... 

The pentahydrate is a white crystalline solid very hygroscopic refractive index 1.60 very soluble in water the aqueous solution acidic soluble in alcohol... 

Stoichiometric hydrates are the most important solvates affecting the solubility of marketed pharmaceuticals. Hemihydrates, monohydrates, and dihydrates are the most common stoichiometric ratios of water incorporated into the crystalline lattice of drugs. Pfeiffer et al. (1970) have shown how different hydrates of cephalosporins could be isolated from solvent systems of varying water activity. Cephalexin has a monohydrate and a dihydrate form, which are stable under different relative humidity conditions. Cefazolin has a monohydrate, a sesquihydrate (1.5 moles water), and a pentahydrate form (Byrn and Pfeiffer, 1992). Jozwiakowski et al. (1996) have found that lamivudine can form a 0.2 hydrate, where only one of L ve lamivudine molecules in the crystal lattice is associated with a water molecule. Multiple solvates can be formed for the same drug Stephenson et al. (1994) have shown that dithromycin can crystallize in at least nine solvate forms, including a cyclohexane trisolvate and an acetonitrile trihydrate. In addition, Byrn et al. (1995) have noted that desolvated forms of some drugs have unique properties that differ from their nonsolvated counterparts. 

Raffinose crystallizes from water, or from aqueous alcohols or acetic acid, as the pentahydrate, of m.p. 78°, [a]20D + 105.2° (c 4, in water). No crystalline, characterizing derivatives of raffinose are known. Raffinose may be exactly identified by comparison of its x-ray diffraction powder pattern with that of an authentic standard.28 Other information of value in the identification of raffinose is its extreme ease of acid hydrolysis... 

Notes Borax is available as borax, pentahydrate, but most commonly as borax, decahydrate, the form used in photographic formulas. The old term for decahydrate is crystalline. Borax, decahydrate, and 20 Mule Team Borax are one and the same. 

The hydrate contains water as an integral part of the crystalline structure of the compound. When salt crystallizes from an aqueous solution, the number of water molecules bound to the metal ion are characteristic of the metal and are in a definite proportion. Thus when copper sulfate crystallizes from water, the blue salt copper(II) sulfate pentahydrate, CuS04-5H20, forms. As indicated by the formula, 5 waters of hydration are bound to the copper(II) ion in copper sulfate. Notice how the formula is written—the waters of hydration are separated from the formula of the salt by a dot. 

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