Heptahydrate

Evaporation and crystallisation of the sodium sulphite solution gives crystals of the heptahydrate NajSOj.THjO. However, on evaporation of the hydrogensulphite solution, the solid obtained is chiefly sodium pentaoxodisulphate(IV) ( metabisulphite ) Na2S20j, and contains little if any of the hydrogensulphite. However, the hydrogen sulphite ion is obtained when the solid redissolves in water ... 

Other iron(If) salts include, notably the green sulphate heptahydrate FeS04.7H2O which on heating yields first the white anhydrous salt FeS04 and then decomposes ... 

Granular magnesium sulphate Is prepared by heating the heptahydrate gently (at 150-175°) in an oven until most of the water of hydration has been... 

Mineral hydrates, such as alumina trihydrate and magnesium sulfate heptahydrate, are used in highly filled thermoset resins. 

Standard Zinc Solution. Dissolve exactly 13.629 g of zinc chloride, ACS reagent grade, or 28.754 g of zinc sulfate heptahydrate, and dilute to 1 E for O.IOOOM solution. 

A mixed valency pale yeHow crystalline iron pentafluoride heptahydrate, FeF 7H20, is prepared by dissolving iron powder in 40% HF in the presence of air (16). No appHcations have been reported for this material. 

Magnesium sulfate heptahydrate may be prepared by neutralization of sulfuric acid with magnesium carbonate or oxide, or it can be obtained directly from natural sources. It occurs abundantly as a double salt and can also be obtained from the magnesium salts that occur in brines used for the extraction of bromine (qv). The brine is treated with calcium hydroxide to precipitate magnesium hydroxide. Sulfur dioxide and air are passed through the suspension to yield magnesium sulfate (see Chemicals frombrine). Magnesium sulfate is a saline cathartic. 

Sulfates. Iron(II) sulfate heptahydrate [7782-63-0] FeSO forms blue-green monoclinic crystals that are very soluble in water and... 

The main impurity of the filtrate is the iron(II) sulfate which can be crystallized as the heptahydrate, FeS04-7H2 O, by cooling the solution to a temperature below 15°C. This process is most often carried out in vacuum crystallizers. The crystals of iron sulfate are separated by centrifugation or filtration (qv). To prevent premature hydrolysis of titanium dioxide, the temperature of the above processes should not exceed 70°C. 

The largest volume of synthetic red iron oxide is produced by the two-step calcination of iron(II) sulfate. In the first step, the iron(II) sulfate heptahydrate is dehydrated to a monohydrate ... 

Physical Properties. Anhydrous sodium sulfite [7757-83-7] Na2S02, is an odorless, crystalline soHd and most commercial grades other than by-product materials are colorless or off-white (331—334). It melts only with decomposition. The specific gravity of the pure soHd is 2.633 (15.4°C). Sodium sulfite is quite soluble in water. It has a maximum solubiHty of 28 g/100 g sol at 33.4°C at higher and lower temperatures, it is less soluble in water. Below this temperature, the heptahydrate crystallizes above this temperature, the anhydrous salt crystallizes. Sodium sulfite is soluble in glycerol but insoluble in alcohol, acetone, and most other organic solvents. 

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. 

The solubihty of zinc sulfate increases almost linearly with temperature from 27.6 wt % (as ZnSO at —7° C to 41.4 wt % at 39°C. In this range, the heptahydrate is the soHd phase. As the temperature rises, the soHd phase becomes the hexahydrate and its solubihty increases to a maximum of 47.7 wt % at 70°C. Above this temperature, the soHd phase is the monohydrate and solubihty declines with temperature to 44.0 wt % at the boiling point (105°C). 

Ziac sulfate was made by 15 companies ia 1980 from secondary materials (93%) and from roasted ore, ie, ziac oxide (7%). The ziaciferous material reacts with sulfuric acid to form a solution, which is purified. After filtration, the solution is heated to evaporation and heptahydrate crystals are separated. It is sometimes sold ia this form but usually as the monohydrate [7446-19-7] which is made by dehydration at ca 100°C. Very pure ziac sulfate solution is made ia the manufacture of the pigment Hthopone [1345-05-7] ZnS-BaSO, and of ziac by electrowinning (see ZiNC AND ZINC ALLOYS). 

Dicesium tetraborate pentahydrate [12228-83-0] 5H20, and dicesium diborate heptahydrate [66634-85-3] Qs O 7H20, also exist. 

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... 

Cobalt(Il) sulfate heptahydrate [10026-24-17, CoSO is a reddish pink monoclinic crystalline material that effloresces in dry air to form the... 

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