Zinc bromide ( Zn Br₂) is an

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemis ...

with the chemical formula Zn Br₂. It is a colourless salt that shares many properties with

zinc chloride Zinc chloride is the name of inorganic chemical compounds with the formula ZnCl2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white, and are highly soluble in water. This salt is hygroscopic ...

(ZnCl₂), namely a high solubility in water forming acidic solutions, and good solubility in organic solvents. It is

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance' ...

and forms a dihydrate ZnBr₂·2H₂O.

Production

ZnBr₂ · 2H₂O is prepared by treating zinc oxide or zinc metal with

hydrobromic acid Hydrobromic acid is a strong acid formed by dissolving the diatomic molecule hydrogen bromide (HBr) in water. "Constant boiling" hydrobromic acid is an aqueous solution that distills at and contains 47.6% HBr by mass, which is 8.77 mol/L. ...

. : ZnO + 2HBr + H₂O → ZnBr₂·2H₂O : Zn + 2HBr → ZnBr₂ + H₂ The anhydrous material can be produced by dehydration of the dihydrate with hot CO₂ or by reaction of zinc metal and bromine. Sublimation in a stream of hydrogen bromide also gives the anhydrous derivative.

Structure

ZnBr₂ crystallizes in the same structure as ZnI₂: four tetrahedral Zn centers share three vertices to form “super-tetrahedra” of nominal composition ²⁻, which are linked by their vertices to form a three-dimensional structure. The dihydrate ZnBr₂ · 2H₂O can be described as ( n(H₂O)₆sup>2+)²( n₂Br₆sup>2-). Gaseous ZnBr₂ is linear in accordance with

VSEPR Valence shell electron pair repulsion (VSEPR) theory ( , ), is a model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms. It is also named the Gillespie-Nyholm the ...

theory with a Zn-Br bond length of 221 pm.

Uses

Zinc bromide is used in the following applications: * In

organic chemistry Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J ...

as a

Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

. * It is the

electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon ...

in the zinc bromide battery. * In oil and natural gas wells, solutions containing zinc bromide are used to displace drilling mud when transitioning from the drilling phase to the completion phase or in well workover operations. The extremely dense brine solution gives the fluid its weight of 20 pounds/gallon, which makes it especially useful in holding back flammable oil and gas particles in high pressure wells. However, the high acidity and

osmolarity Osmotic concentration, formerly known as osmolarity, is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per litre (L) of solution (osmol/L or Osm/L). The osmolarity of a solution is usually expressed as Osm/L ...

cause corrosion and handling problems. Crews must be issued slicker suits and rubber boots because the fluid is so dehydrating. * Zinc bromide solutions can be used as a transparent shield against

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...

. The space between two

glass Glass is a non- crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenchin ...

panes is filled with a strong aqueous solution of zinc bromide with a very high

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...

, to be used as a window on a

hot cell Shielded nuclear radiation containment chambers are commonly referred to as hot cells. The word "hot" refers to radioactivity. Hot cells are used in both the nuclear-energy and the nuclear-medicines industries. They are required to protect in ...

. This type of window has the advantage over

lead glass Lead glass, commonly called crystal, is a variety of glass in which lead replaces the calcium content of a typical potash glass. Lead glass contains typically 18–40% (by weight) lead(II) oxide (PbO), while modern lead crystal, historically a ...

in that it will not darken as a result of exposure to radiation. All glass will darken slowly over time due to radiation, however this is especially true in a hot cell, where exceptional levels of radiation are present. The advantage of an aqueous salt solution is that any radiation damage will last less than a

millisecond A millisecond (from '' milli-'' and second; symbol: ms) is a unit of time in the International System of Units (SI) equal to one thousandth (0.001 or 10−3 or 1/1000) of a second and to 1000 microseconds. A unit of 10 milliseconds may be calle ...

, so the shield will undergo self-repair.

Safety

Safety considerations are similar to those for zinc chloride, for which the toxic dose for humans is 3–5 g.

References

{{bromine compounds

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

Metal halides

bromide A bromide ion is the negatively charged form (Br−) of the element bromine, a member of the halogens group on the periodic table. Most bromides are colorless. Bromides have many practical roles, being found in anticonvulsants, flame-retardant ...

Production

Structure

Uses

Safety

See also

References