Potassium bromide

Crystal structure
__ K +      __ Br -
Crystal system	cubic
Space group	Fm 3 m (No. 225)
Coordination numbers	K [6], Br [6]
General
Surname	Potassium bromide
other names	Potassium bromide Potassium bromate
Ratio formula	KBr
Brief description	colorless, hygroscopic crystals
External identifiers / databases
CAS number 7758-02-3 EC number 231-830-3 ECHA InfoCard 100.028.937 PubChem 253877 Wikidata Q2546
properties
Molar mass	119.01 g mol −1
Physical state	firmly
density	2.75 g cm −3 (20 ° C)
Melting point	732 ° C
boiling point	1435 ° C
Vapor pressure	1.3 h Pa (795 ° C)
solubility	easily in water (650 g l −1 at 20 ° C)
Refractive index	1.5598
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 319 P: 305 + 351 + 338
Toxicological data	3070 mg kg −1 ( LD 50 ,  rat ,  oral )
Thermodynamic properties
ΔH f 0	−392 kJ mol −1
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Potassium bromide is the potassium - salt of hydrobromic forms, the colorless crystal dice even better than potassium chloride are soluble in water.

presentation

The classic method for the production of KBr takes place from the reaction between potassium carbonate and iron (II, III) bromide. The Fe ₃ Br ₈ is produced beforehand from scrap iron with excess bromine and a layer of water:

${\displaystyle {\ce {4K2CO3 + Fe3Br8 -> 8KBr + Fe3O4 + 4CO2}}}$

In the laboratory, for example, potassium bromide can be produced by reacting potassium hydroxide solution with bromine in an ammoniacal solution. This also creates water and nitrogen :

${\displaystyle {\ce {6KOH + 3Br2 + 2NH3 ->6KBr + 6H2O + N2}}}$

The bromination of potash also provides potassium bromide, the less soluble potassium bromate is deposited:

${\displaystyle {\ce {3K2CO3 + 3Br2 -> 5KBr + KBrO_3 v + 3CO2 ^}}}$

The production from the elements has no technical meaning:

${\displaystyle {\ce {2K + Br2 -> 2KBr}}}$

The equations of the ion formation reaction are:

Partial equations:

${\displaystyle {\ce {TG1: K -> K ^{+}+ 1e-}}}$

${\displaystyle {\ce {TG2: Br_2 + 2e- -> 2Br^{-}}}}$

Overall equation:

${\displaystyle {\ce {GS: 2K + Br_{2}-> 2K^+ + 2Br^{-}}}}$

properties

Potassium bromide behaves like a cold liquid under pressure and appears transparent in IR light. It does not form hydrates .

The standard enthalpy of formation of potassium bromide is Δ H _f ⁰  = −392 kJ / mol.

The salt is very soluble in water. The solubility increases with increasing temperature.

solubility in water
temperature	in ° C	−10	0	20th	40	60	80	100	120
solubility	in g / 100 g H 2 O	48.8	54.0	65.6	76.1	85.9	95.3	105	115

Potassium contains 0.0118% of the isotope ⁴⁰ K, this provides 10242 Bq per kilogram KBr, of which 89.28% is beta radiation and 10.72% is gamma radiation with 1.46083 MeV.

use

Potassium bromide

Potassium bromide is used to produce silver bromide emulsions on films and plates for photographic films. In photographic developers, it counteracts fogging and delays development.

Because of the high optical transparency for electromagnetic waves in the range from 0.23 to 26.0 μm, single crystals of KBr are used for the production of optical components, such as e.g. B. Lenses and prisms, used for infrared optics. Since it also flows slightly cold (see above), solids for infrared spectroscopy are embedded in it, so-called potassium bromide pellets.

Potassium bromide was also used as the mid-19th century medicines for the treatment of seizures and as a sedative used. It is thus the oldest anti-epileptic . At that time z. Sometimes very high doses were used, which led to chronic bromine poisoning. This so-called bromism was characterized by excessive sedation , dizziness, headaches, lack of concentration, loss of memory, hallucinations, or rhinitis. Skin symptoms such as bromine acne or bromoderm with painful, purulent skin lumps (mostly on the limbs ) also often appeared . In the first half of the 20th century, the bromine preparations were replaced by the barbiturates .

Even today, potassium bromide is used as Dibro-Be mono for the treatment of a special form of epilepsy, the early childhood grand mal epilepsy. Bromism is rare now that lower doses are used. Today it is no longer used as a sedative.

Individual evidence

1. ↑ ^{a b c d e f g} Entry on potassium bromide in the GESTIS substance database of the IFA , accessed on February 17, 2017(JavaScript required) .
2. ↑ ^{a b} Data sheet potassium bromide (PDF) from Merck , accessed on January 19, 2011.
3. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Index of Refraction of Inorganic Crystals, pp. 10-246.
4. ^ AF Holleman , N. Wiberg : Inorganische Chemie . 103rd edition. Volume 1: Basics and main group elements. Walter de Gruyter, Berlin / Boston 2016, ISBN 978-3-11-049585-0 (Reading sample: Part A - Basics of the chemistry of hydrogen. Google book search ).
5. ↑ Chemdat .
6. ^ ^{A b c} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 , p. 1170.
7. ↑ ^{a b} Yoffe, D .; Frim, R .; Ukeles, SD; Dagani, MJ; Barda, HJ; Benya, TJ; Sanders, DC: Bromine Compounds , in: Ullmanns Enzyklopädie der Technischen Chemie , Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2013; doi : 10.1002 / 14356007.a04_405.pub2 .
8. ^ Locock C. Discussion of a paper by EH Sieveking: Meeting of the Royal Medical and Surgical Society of London. Lancet. 1857; 1: 527.
9. ↑ Hans Bangen: History of the drug therapy of schizophrenia. Berlin 1992, ISBN 3-927408-82-4 . P. 24