984 ZINC CARBONATE

Uses

Zinc bromide is used in preparing photographic emulsions, and in producing rayon. Concentrated solution is used as a shield in viewing windows for nuclear reactions.

Physical Properties

White crystalline powder; sharp metallic taste; orthorhombic structure; refractive index 1.5452; density 4.20 g/cm3; very hygroscopic; melts at 394°C; vaporizes at 650°C; highly soluble in water 447g/100 mL at 20°C; aqueous solution acidic; very soluble in alcohol, ether, and acetone; soluble in alkali hydroxides and ammonia solution.

Thermochemical Properties
∆Ηƒ° (ZnBr2)	–78.55kcal/mol
∆Ηƒ° (ZnBr2•2H2O)	–224.0 kcal/mol
∆Gƒ° (ZnBr2•2H2O)	–191.1 kcal/mol
∆Gƒ° (ZnBr2)	–74.60 kcal/mol
S° (ZnBr2)	33.1 cal/deg mol
S° (ZnBr2•H2O)	47.5 cal/deg mol

Preparation

Zinc bromide is prepared by mixing barium bromide and zinc sulfate solutions. The product barium sulfate is removed by filtration and the filtrate is evaporated to obtain crystals of zinc bromide:

BaBr2 + ZnSO4 → ZnBr2 + BaSO4

Zinc bromide also may be prepared by the action of zinc with hydrobromic acid followed by crystallization.

Analysis

Elemental composition: Zn 29.03%, Br 70.97%

An aqueous solution is analyzed for zinc metal (see Zinc) by AA, ICP, and other methods, and for Br¯ by ion chromatography.

ZINC CARBONATE

[3486-35-9]

Formula ZnCO3; MW 125.39

Occurrence and Uses

Zinc carbonate occurs in nature as mineral smithsonite and zincspar. The compound is used in ceramics and fire proofing filler for rubber and plastics.

ZINC CHLORIDE 985

Also, it is used in lotions, ointments, cosmetics, and as a topical antiseptic.

Physical Properties

White crystalline solid; orthorhombic structure; refractive index 1.818; Mohs hardness 4.3; density 4.398 g/cm3; decomposes at 300°C forming zinc oxide; practically insoluble in water, 10 mg/L at 15°C; soluble in acids, alkalis, and ammonium salt solutions.

Thermochemical Properties
∆Hƒ°	–194.3 kcal/mol
∆Gƒ°	–174.8 kcal/mol
S°	19.7 cal/deg mol
Cρ	19.05 cal/deg mol

Production

Zinc carbonate is derived from its mineral smithsonite. Also, the compound may be prepared by the reaction of sodium bicarbonate with a soluble zinc salt:

ZnCl2 + NaHCO3 → ZnCO3 + NaCl + HCl

Analysis

Elemental composition: Zn 52.14%, C 9.58%, O 38.28%. Zinc carbonate is identified by effervescence produced upon adding dilute HCl. CO2 evolved is identified by the lime water test or by GC or GC/MS. Characteristic mass for identification of CO2 is 44. Zinc may be analyzed in an acid solution by AA, ICP, and other methods to measure zinc content of the compound.

ZINC CHLORIDE

[7646-85-7]

Formula ZnCl2; MW 136.29

Uses

Zinc chloride is used as a wood preservative and in fireproofing timber. Other uses are as a deodorant in disinfecting fluids; in dental cements; in electroplating; in etching metals and glass; as flux for soldering; as a mordant in printing and dyeing textiles; in making dry batteries; in denaturing alcohols; in vulcanizing rubber; in manufacturing parchment; in making artificial silk; in making activated carbon and cold-water glues; and in refining petroleum. Also, zinc chloride is used as a dehydrating and condensing agent in organic syntheses. In medicine it is used as an astringent and antiseptic.

Physical Properties

White crystalline powder or granules; hygroscopic; density 2.907 g/cm3; melts at 290°C; vaporizes at 732°C; vapor pressure 1 torr at 428°C and 20 torr

986 ZINC CYANIDE

at 536°C; highly soluble in water, 432 g/100mL at 25°C; aqueous solution acidic in litmus test; also soluble in ethanol, glycerol, and acetone.

Thermochemical Properties
∆Hƒ° (cry)	–99.2 kcal/mol
∆H ƒ° (gas)	–63.6 kcal/mol
∆G ƒ° (gas)	–88.3 kcal/mol
S° (cry)	26.6 cal/deg mol
Cρ (cry)	17.0 cal/deg mol
∆Hfus	30.1 kcal/mol

Preparation

Zinc chloride is prepared by the reaction of zinc oxide or zinc metal with dilute hydrochloric acid, followed by crystallization:

ZnO + 2HCl → ZnCl2 + H2O

Zn + 2HCl → ZnCl2 + H2

Analysis

Elemental composition: Zn 47.97%, Cl 52.03%. The compound usually contains small amounts of oxychloride and water. An aqueous solution may be analyzed for zinc by AA, ICP, and other methods (See Zinc), and for chloride ion by titration against a standard solution of silver nitrate using potassium chromate indicator. Chloride ion also may be determined by ion chromatography after sufficient dilution.

Toxicity

Inhalation of zinc chloride fumes can injure lungs and respiratory tract. Dusts or fumes also cause dermatitis, boils, conjunctivitis, and gastrointestinal tract upset (Lewis(Sr), R.J. 1996. Sax’s Dangerous Properties of Industrial Materials, 9th ed. New York: Van Nostrand Reinhold).

LD50 oral (rat): 350mg/kg

LCLO (inhalation): 1.960 g/m3/10 min

ZINC CYANIDE

[557-21-1]

Formula Zn(CN)2; MW 117.42

Uses

Zinc cyanide is used in electroplating; as an insecticide; and for separating ammonia from producer gas.

Physical Properties

White powder; orthorhombic crystals; density 1.852 g/cm3; decomposes at

ZINC FLUORIDE 987

800°C; insoluble in water (about 5mg/L at 20°C); soluble in alkalies, potassium cyanide and ammonia solutions; insoluble in alcohol.

Thermochemical Properties

∆Ηƒ°	22.9 kcal/mol

Preparation

Zinc cyanide is precipitated by mixing solutions of potassium cyanide and a soluble zinc salt, such as zinc chloride or sulfate:

Zn2+ (aq) + 2CN¯(aq) → Zn(CN)2(s)

Analysis

Elemental composition: Zn 55.68%, C 20.46%, N 23.86%. A small and measured amount is treated with dilute sulfuric acid. Hydrogen cyanide generated is swept with a purging gas and collected in sodium hydroxide solution. The solution is analyzed for cyanide by a colorimetric method using pyridinebarbituric acid reagent or by cyanide ion-specific electrode (See Hydrogen Cyanide, Analysis). The acid solution may be analyzed for zinc to measure its content in the compound.

Toxicity

The compound is toxic by oral and intraperitoneal routes. The intraperitoneal lethal dose in rat is 100 mg/kg.

ZINC FLUORIDE

[7783-49-5]

Formula ZnF2; MW 103.39; forms a tetrahydrate, ZnF2•4H2O [13986-18-0], MW 175.45

Uses

Zinc fluoride is used in the manufacture of phosphors for fluorescent lights. It also is used in electroplating baths, in preservation of wood, in glazes and enamels for ceramics, and in fluorination reactions of organics.

Physical Properties

Anhydrous zinc fluoride is a white hygroscopic solid; tetragonal needles; density 4.9 g/cm3; melts at 872°C; vaporizes at 1,500°C; vapor pressure 1 torr at 1,243°C and 5 torr at 1,328°C; practically insoluble in water, 5.2 mg/L; sparingly soluble in HCl, HNO3 and ammonia solution.

The hydrated salt, ZnF2•4H2O, is a white crystalline solid; rhombohedral crystals; density 2.30 g/cm3; loses water of crystallization at 100°C; sparingly