8 junio, 2024

Potassium bromide (KBr): structure, properties, uses

He potassium bromide It is an inorganic salt whose chemical formula is KBr. It is formed by the electrostatic union of a bromide anion, Br–, and a potassium cation, K+, in a 1:1 ratio; that is, we have the same amount of Br– as K+ in the KBr crystals.

Potassium bromide is a solid white or crystalline salt, it is odorless, very soluble in water, and slightly soluble in ethanol and ether. It was used during the final part of the 19th century and much of the 20th century in the treatment of epilepsy and as a sedative.

Until 1975 it continued to be sold freely, the year in which its use decreased due to the toxic effects it produced on patients. Currently it is still used in several species of animals in the treatment of seizures, although from 1912 it was replaced by sodium phenobarbital.

Potassium bromide is used in optical studies corresponding to the near-infrared region of the electromagnetic spectrum. It also serves as material used in the field of photography.

[toc]

link type

Potassium bromide is a binary salt, product of the combination of a bromine atom with an oxidation state -1, with a potassium atom with an oxidation state +1. Therefore, an electrical attraction is established between the Br– ion and the K+ ion.

This type of electrical or electrostatic interaction is known as an ionic bond, which dissociates when the potassium bromide salt dissolves in water, releasing the K+ and Br– ions.

These ions are separated by the property of water to keep electrical charges of opposite sign separated.

Potassium bromide structure

Potassium bromide has a face-centered cubic (fcc) crystal structure: face-centered cubic), equal to that observed in sodium chloride.

In this structure, each Br– anion is bound or coordinated with six K+ cations, and in turn, each K+ has six Br– as neighbors in the crystal lattices.

Nomenclature

Potassium bromide is classified as an alkali metal halide or halide. The names of these salts are constructed by removing the final letter of the halogen name (chlorine, bromine, iodine, fluorine, and astatine), with the exception of fluorine, and replacing the final letter with the suffix -ide. The name of the metal is written below without modification.

For example: sodium chloride, potassium iodide, calcium fluoride, etc. That is why KBr is called potassium bromide or potassium bromide (according to the traditional nomenclature).

Potassium bromide properties

Physical appearance

Colorless crystal, crystalline or white powder or granules.

Smell

Lavatory

Flavor

At a high concentration it has a bitter and pungent taste.

molar mass

119.02 g/mol

Density

2.74 g/cm3 at 25ºC

Melting point

734ºC

Boiling point

1435ºC

Water solubility

535 g/L at 0ºC

678 g/L at 25ºC

1020 g/L at 100ºC

1 gram of the salt dissolves in 1 mL of boiling water, indicating that it is highly soluble in water.

glycerol solubility

217g/L

1 gram of potassium bromide dissolves in 4.6 mL of glycerol.

Solubility in ethanol

47.6 g/L at 80ºC.

1 gram of potassium bromide is dissolved in 250 mL of ethanol.

Vapor density

7.14 in relation to the air taken as the unit.

Stability

Stable if stored under recommended conditions. Incompatible with oxidizing agents, strong acids, bromine trifluoride and bromine trichloride.

Decomposition

When heated to decomposition emits harmful products such as hydrogen bromide and potassium oxide.

Refractive index (nD)

1,559

pH

In aqueous solution it produces a neutral pH, around 7.

ignition point

1435ºC

Dissolution and reactivity

In aqueous solution, KBr completely dissociates to give a neutral pH solution.

The salt is a source of bromide that can be used for the production of silver bromide, AgBr, a compound used in developing photographs:

KBr (aq) + AgNO3 (aq) → AgBr (s) + KNO3 (aq)

Also, KBr is a weak reducing agent, incompatible with mercury and silver salts. Produces a violent reaction with bromine trifluoride. It can react with many salts, alkaloids and starch.

It also reacts with acids, for example with concentrated sulfuric acid, releasing hydrogen bromide.

Applications

Treatment of epilepsy and seizures

The anticonvulsant properties of potassium bromide were first exposed by Sir Charles Locock, at a meeting of the Royal Medicine and Chirurgical Society in 1857, which prompted its use in the treatment of epilepsy.

Potassium bromide was used as the priority drug in the treatment of epilepsy and as a sedative until 1912, when sodium phenobarbital was introduced.

Even so, it continued to be used as an adjunct to sodium phenobarbital in the treatment of seizures associated with epilepsy.

In 1975, due to its toxic nature, the US FDA (Food & Drug Administration) decided to no longer recommend the use of potassium bromide, both in humans and in animals. However, some countries continued to administer it.

Potassium bromide has been used as a hypnotic and sedative in cattle, horses, sheep, and pigs. It was also used in the treatment of colic and tetany in horses, and in the treatment of convulsions in dogs.

infrared optics

Due to the transparency of potassium bromide in a range of wavelengths between ultraviolet and near-infrared light, it is used as a component of windows for various electromagnetic radiations, especially infrared radiations.

Several techniques are used in this regard. One of them consists of making two crystalline disks of potassium bromide, placing a film of the material to be analyzed in the infrared between the disks. The studies are carried out in the near infrared between 780 nm and 3000 nm.

Photography

Potassium bromide has had numerous uses and applications in photography, for example, it has been used to formulate photographic developers, in the manufacture of photographic film, as a film thickener, and as a color photographic whitener.

It is used to improve the differentiation between exposed and unexposed silver halide crystals, to increase the print density of thin negatives, and as a secondary halide, in combination with iodides, for processing paper negatives.

It has also been used in combination with bichloride of mercury, copper sulfate, or potassium ferricyanuride in photographic whiteners. It has also served as a limiter in alkaline developers used for gelatin plates and developing papers.

Chemical analysis

KBr is used in the determination of the valuation of copper and silver, in the polarographic analysis of indium, cadmium and arsenic.

Other uses

It is used in lithography engraving processes, in oil processing, in the thermal stabilization of nylon, in the manufacture of fibers, and finally in the manufacture of special soaps.

References

Whitten, Davis, Peck & Stanley. (2008). Chemistry. (8th ed.). CENGAGE Learning.
Shiver & Atkins. (2008). Inorganic chemistry. (Fourth edition). Mc Graw Hill.
Day, R., & Underwood, A. (1986). Quantitative Analytical Chemistry (fifth ed.). PEARSON Prentice Hall.
Wikipedia. (2020). Potassium bromide. Retrieved from: en.wikipedia.org
National Center for Biotechnology Information. (2021). Potassium bromide. PubChem Compound Summary for CID 253877. Retrieved from: pubchem.ncbi.nlm.nih.gov
Emea. (1999). Bromide, Potassium Salt: Summary Report. [PDF]. Retrieved from: ema.europa.eu
The Sevier BV (2020). Potassium Bromide. Science Direct. Retrieved from: sciencedirect.com

Deja una respuesta

Tu dirección de correo electrónico no será publicada. Los campos obligatorios están marcados con *