Salts hydrates

Cobalt II) halides can be obtained by direct combination of the elements, or by dehydration of their hydrates. Anhydrous cobalt(II) chloride is blue, and the solid contains octahedrally-coordinated cobalt the hydrated salt C0CI2. bHjO is pink, with each cobalt surrounded by four water molecules and two chloride ions in a distorted octahedron. 

Nickel forms yellow anhydrous halides NiXjlX = F. Cl. Br) and a black iodide Nil2 all these halides are made by direct combination of the elements, and the chloride by reaction of sulphur dichloride oxide with the hydrated salt. All dissolve in water to give green solutions from which the hydrates can be crystallised the solutions contain the ion [NifHjOls], and the chloride crystallises as NiCl2.6H2O, nickel(II) chloride hexahydrate. 

The anhydrous chloride is prepared by standard methods. It is readily soluble in water to give a blue-green solution from which the blue hydrated salt CuClj. 2H2O can be crystallised here, two water molecules replace two of the planar chlorine ligands in the structure given above. Addition of dilute hydrochloric acid to copper(II) hydroxide or carbonate also gives a blue-green solution of the chloride CuClj but addition of concentrated hydrochloric acid (or any source of chloride ion) produces a yellow solution due to formation of chloro-copper(ll) complexes (see below). 

Zincill) chloride. ZnCl2, is the only important halide—it is prepared by standard methods, but cannot be obtained directly by heating the hydrated salt. It has a crystal lattice in which each zinc is surrounded tetrahedrally by four chloride ions, but the low melting point and solubility in organic solvents indicate some covalent... 

Table 14.2 shows that all three elements have remarkably low melting points and boiling points—an indication of the weak metallic bonding, especially notable in mercury. The low heat of atomisation of the latter element compensates to some extent its higher ionisation energies, so that, in practice, all the elements of this group can form cations in aqueous solution or in hydrated salts anhydrous mercuryfll) compounds are generally covalent. 

For this preparation, it is particularly necessary that the sodium acetate should be free from traces of water. The anhydrous material can be prepared by gently heating the hydrated salt (CHsCOONa,3HjO) in an esaporating-basin over a small Bunsen flame. The salt dissolves in its water of ciystallisation and resolidifies as this water is driven off further heating then causes the anhydrous material to melt. Stir the molten anhydrous material to avoid charring, and then allow it to cool in a desiccator. Powder the cold material rapidly in a mortar, and bottle without delay. 

Anhydrous sodium sulphide. The hydrated salt, NajS.QH O, is heated in a Pyrex distilling flask or retort in a stream of hydrogen or of nitrogen until water ceases to be evolved. The solid cake of anhydrous sodium sulphide is removed from the vessel with the aid of a copper wire hook or by other suitable means. No attempt should be made to fuse the sodium sulphide since at high temperatiues sodium sulphide is readily oxidised to sodium sulphate. 

These hydrated salts contain bidentate carbonate ligands and no water molecules are bound directly to the central metal atom. The only single-crystal x-ray diffraction studies available are those for salts of (4) (52—54) and the mineral tuliokite [128706 2-3], Na2BaTh(C03)2 -6H20], which contains the unusual Th(C02) 2 anion (5) (55). 

Titanium Trichloride Hexahydrate. Titanium trichloride hexahydrate [19114-57-9] can be prepared by dissolving anhydrous titanium trichloride ia water or by reduciag a solutioa of titanium tetrachloride. Evaporation and crystallisation of the solution yield violet crystals of the hexahydrate. The hydrated salt has had some commercial appHcation as a stripping or bleaching agent ia the dyeiag iadustry, particularly where chlorine must be avoided. 

Anhydrous metal borates may be prepared by heating the hydrated salts to 300—500°C, or by direct fusion of the metal oxide with boric acid or B2O2. Many binary and tertiary anhydrous systems containing B2O2 form vitreous phases over certain ranges of composition (145). 

CeOCl. The anhydrous cerous chloride [7790-86-5] can be made from the hydrated salt by suppressing oxyhahde formation during thermal dehydration by the presence of hydrogen chloride or ammonium chloride. The anhydrous salt is soluble in a variety of organic solvents, eg, alcohols and ethers, has mp 817°C, and can be volatilized at high temperatures in vacuum. 

Ghromium(II) Compounds. The Cr(II) salts of nonoxidizing mineral acids are prepared by the dissolution of pure electrolytic chromium metal ia a deoxygenated solution of the acid. It is also possible to prepare the simple hydrated salts by reduction of oxygen-free, aqueous Cr(III) solutions using Zn or Zn amalgam, or electrolyticaHy (2,7,12). These methods yield a solution of the blue Cr(H2 0)g cation. The isolated salts are hydrates that are isomorphous with and compounds. Examples are chromous sulfate heptahydrate [7789-05-17, CrSO 7H20, chromous chloride hexahydrate... 

Cu(N03 )26H2 0, is produced by crystallization from solutions below the transition poiat of 26.4°C. A basic copper nitrate [12158-75-7] Cu2(N02)(0H)2, rather than the anhydrous product is produced on dehydration of the hydrated salts. The most common commercial forms for copper nitrate ate the ttihydtate and solutions containing about 14% copper. Copper nitrate can be prepared by dissolution of the carbonate, hydroxide, or oxides ia nitric acid. Nitric acid vigorously attacks copper metal to give the nitrate and evolution of nitrogen oxides. 

The actual yield may be obtained from algebraic calculations or trial-and-error calculations when the heat effects in the process and any resultant evaporation are used to correc t the initial assumptions on calculated yield. When calculations are made by hand, it is generally preferable to use the trial-and-error system, since it permits easy adjustments for relatively small deviations found in practice, such as the addition of wash water, or instrument and purge water additions. The following calculations are typical of an evaporative ciy/staUizer precipitating a hydrated salt, if SI units are desired, kilograms = pounds X 0.454 K = (°F 459.7)/I.8. 

For calculations involving hydrated salts, it is convenient to make the calculations based on the hydrated solute and the free water, ... 

Naphthionic acid (4-aminonaphthalene-l-sulfonic acid) [84-86-6] M 223.3, m > 300°(dec), pK 2.68. It crystallises from H2O as needles of the 0.5 hydrate. Salt solns fluoresce strongly blue. 

Other finite-complex anions occur in the oxyfluorides. For example the hydrated salts K2[- S2F]q0].H20 and Rb2[As2F]oO].H20... 

The most stable solid hypochlorites are those of Li, Ca, Sr and Ba (see below). NaOCl has only poor stability and cannot be isolated pure KOCl is known only in solution, Mg yields a basic hypochlorite and impure Ag and Zn hypochlorites have been reported. Hydrated salts are also known. Solid, yellow, hydrated hypobromites Na0Br.xH20 (x = 5, 7) and K0Br.3H20 can be crystallized from solutions obtained by adding Br2 to cold cone solutions of MOH but the compounds decompose above 0°C. No solid metal hypoiodites have yet been isolated. 

In the crystallization of these hydrated salts from aqueous solutions it is essential that a low pH (high level of acidity) is maintained, otherwise hydrolysis occurs and yellow impurities contaminate the products. Similarly, if the salts are redissolved in water, the solutions turn yellow/brown. The hydrolytic processes are complicated, and, in the presence of anions with appreciable coordinating tendencies, are further confused by displacement of water from the coordination sphere of the iron. However, in aqueous solutions of salts such as the perchlorate the following equilibria are important ... 

Many of the hydrated salts and their aqueous solutions contain the octahedral, pink... 

The oxide (p. 1209), chalcogenides (p. 1210) and halides (p. 1211) have already been described. Of them, the only ionic compound is HgF2 but other compounds in which there is appreciable charge separation are the hydrated salts of strong oxoacids, e.g. the nitrate, perchlorate, and sulfate. In aqueous solution such salts are extensively hydrolysed (HgO is only very weakly basic) and they require acidification to prevent the formation of polynuclear hydroxo-bridged species or the precipitation of basic salts such as Hg(OH)(N03) which contains infinite zigzag chains ... 

Table 30.6 Magnetic and spectroscopic properties of Ln ions in hydrated salts...

Hydrated salts with all the common anions can be crystallized from aqueous solutions and frequently, but by no means invariably, they contain the [Ln(H20)9] + ion. An enormous number of salts of organic acids such as oxalic, citric and... 

The salt was prepared by dissolving the free acid form of the penicillin in the equivalent amount of aqueous sodium bicarbonate and freeze drying the resulting solution. The hydrated salt so obtained was shown by alkalimetric assay to be 94% pure and to contain 6% water. 

Hydrated salts, as a rule, do not make good standards because of the difficulty of efficient drying. However, those salts which do not effloresce, such as sodium tetraborate Na2B407, 10H2O, and copper sulphate CuS04,5H20, are found by experiment to be satisfactory secondary standards.2... 

The Karl Fischer procedure was applied to the determination of water present in hydrated salts or adsorbed on the surface of solids. The procedure, where applicable, was more rapid and direct than the commonly used drying process. A sample of the finely powdered solid, containing 5-10 millimoles (90-180 mg) of water, was dissolved or suspended in 25 mL of dry methanol in a 250-mL glass-stoppered graduated flask. The mixture was titrated with standard Karl Fischer reagent to the usual electrometric end point. A blank titration was also carried out on a 25 mL sample of the methanol used to determine what correction (if any) needed to be applied to the titre obtained with the salt. 

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