CRYSTALLINE HYDRATES — substances which part of crystals water molecules are. Education To. is the cornerstone of use in a lab. to practice of some salts as dehumidifiers [CaCl 2 , Mg (ClO 4 ) 2 , CuSO 4 I. A number of medicinal substances (PASK, sulfaguanidine, quinacrine, analginum, etc.) is produced in a look To. Broad use in medical practice (surgery, orthopedics, stomatology) has gypsum (see), astringencies to-rogo are caused by turning into To. Many salts, including applied in medicine (sodium sulfates, magnesium, zinc, calcium chloride, sodium citrate), are
K. K. represent a special case of kristallosolvat, i.e. the crystals containing molecules of solvent in the structure (see. Solvation ).
To. are formed at crystallization of the corresponding anhydrous substances of water or other solvents, watered, and also owing to pulling by such substances of atmospheric moisture or other ways. The water which is a part To., is called crystallizational. Amount of crystal water in To. can be very variously: from fractional number of moths on mol of anhydrous substance, e.g. CaSO 4 - 0,5H 2 O, to a large amount of water [Al 2 (SO 4 ) 3 - 18H 2 O]. Depending on conditions, hl. obr. temperatures, the same connection can hold various number of water molecules, e.g. CuSO 4 - H 2 O, CuSO 4 - 3H 2 O, CuSO 4 - 5H 2 O. To exist in a look To. some simple substances (nonmetals) and many inorganic and organic compounds of various classes (to - you, the bases, salts, etc.), and also natural minerals can. LiOH-H are examples 2 O, FeSO 4 - 7H 2 O, CH 4 - 5,75H 2 O, CHCl 3 - 17H 2 O, piperazin (with 6H 2 O), caffeine (with 1 H 2 O), cholesterol (with 1 H 2 O). Some To. (e.g., Na 2 CO 3 - 10H 2 O) on air spontaneously lose crystal water or a part it, being exposed to so-called aeration; usually elimination of water from To. (dehydration) demands heating or keeping over dehumidifiers.
To. salts of metals are formed as a result of coordination of water molecules by oxygen atoms around a cation, hydrogen atoms of water can also participate in education To., interacting with anion; types such To. are characterized by features of coordination of water in a crystal lattice. To. gases, hydrocarbons and some other organic compounds represent connections of inclusion in which the main molecules are placed in emptiness of a crystal lattice of ice. See also Hydration , Liquid crystals , Crystallization , Crystals .
Bibliography: Bernal Dzh. D. Rol of water in crystal substances, Usp. chemical, t. 25, century 5, page 643, 1956, bibliogr.; Nekrasov B. V. Fundamentals of the general chemistry, t. 1, page 155, t. 2, page 53, M., 1973.
A. I. Tochilkin.