Silver bromide (I)

Silver bromide
Silver bromide
Are common
Systematic ; name	Silver bromide
Chem. formula	AgBr
Physical properties
condition	solid
Molar mass	187.7722 g / mol g / mol
Density	6.47 g / cm³
Thermal properties
T. melt.	424 ° C
T. bale.	1505 ° C
Like heat resistant.	52.3 J / (mol · K)
Enthalpy of Education	-100.7 kJ / mol
Specific Heat of Evaporation	942600 J / kg
Specific heat of fusion	46865 J / kg
Chemical properties
Solubility in water	g / 100 ml at 20 ° C
Classification
Reg. CAS number
PubChem
Reg. EINECS number
Smiles
Inchi
ChemSpider

Silver bromide (also obsolete. Bromite or bromargirite ^[1] ) is a light yellow crystalline substance, insoluble in water, has an ionic structure.

Content

Physical Properties

Diamagnetic yellow cubic face-centered crystals, space group Fm3m, Z = 4 (a = 0.5549 nm). At temperatures> 259 ° C, it goes into the rhombic modification.

May form colloidal solutions.

Getting

Known for the natural mineral bromargirite ( born Bromargyrite ) consisting of AgBr with impurities of chlorine and iodine. Represents transparent or translucent crystals, yellowish, greenish-brown or bright green, depending on impurities. Deposits in Mexico , Chile and Western Europe .

Silver bromide can be obtained by reacting any soluble silver salt with a solution of any bromide or hydrobromic acid . Most commonly used is silver nitrate and potassium or sodium bromide:

{\mathsf {AgNO_{3}+NaBr\rightarrow AgBr\downarrow +NaNO_{3}}}

{\ displaystyle {\ mathsf {AgNO_ {3} + NaBr \ rightarrow AgBr \ downarrow + NaNO_ {3}}}}

In this reaction, a precipitate of finely crystalline slightly yellow silver bromide. This reaction is often used in analytical chemistry for the qualitative and quantitative determination of silver. Under certain conditions (purity and concentration), a colloidal solution may form instead of a precipitate.

It is possible to obtain silver bromide directly from the elements:

{\mathsf {2Ag+Br_{2}{\xrightarrow {150-200^{o}C}}2AgBr}}

{\ displaystyle {\ mathsf {2Ag + Br_ {2} {\ xrightarrow {150-200 ^ {o} C}} 2AgBr}}}

Chemical Properties

Like many other silver compounds, bromide is able to form soluble complexes with some ligands (CN ^- , NH ₃ , etc.):

{\mathsf {AgBr+2CN^{-}\rightarrow [Ag(CN)_{2}]^{-}+Br^{-}}}

{\ displaystyle {\ mathsf {AgBr + 2CN ^ {-} \ rightarrow [Ag (CN) _ {2}] ^ {-} + Br ^ {-}}}}

{\mathsf {AgBr+2NH_{3}\rightarrow [Ag(NH_{3})_{2}]^{+}+Br^{-}}}

{\ displaystyle {\ mathsf {AgBr + 2NH_ {3} \ rightarrow [Ag (NH_ {3}) _ {2}] ^ {+} + Br ^ {-}}}}

Silver bromide undergoes photolytic dissociation:

{\mathsf {2AgBr{\xrightarrow {h\nu }}2Ag+Br_{2}}}

{\ displaystyle {\ mathsf {2AgBr {\ xrightarrow {h \ nu}} 2Ag + Br_ {2}}}}

This reaction underlies most photographic processes.

In chemical laboratories, as a rule, waste from working with silver compounds is not discarded, but regenerated again. To do this, the precipitation mixture of silver salts is separated from the silver-free supernatant, washed and reacted with zinc and a small amount of strong mineral acid (for example, sulfuric). Since the precipitation of silver salts is sparingly soluble, the concentration of silver ions over the precipitate is low, so the reaction with zinc proceeds very slowly (a day or more). Reaction Scheme:

{\mathsf {AgBr{\xrightarrow[{H_{2}SO_{4}}]{Zn}}Ag}}

{\ displaystyle {\ mathsf {AgBr {\ xrightarrow [{H_ {2} SO_ {4}}] {Zn}} Ag}}}

Silver in this reaction is released in the form of a gray fine powder. After that, it can be melted or dissolved in nitric acid to form silver nitrate - the main silver preparation from which the remaining compounds are obtained.

Application

The phenomenon of photodissociation of silver bromide is used in photography (in black and white or mixed with sensitizers in color). Also, silver bromide is used to create special glasses that change their transparency in different light conditions. Upon irradiation of glass with an admixture of silver bromide, the latter decomposes with the formation of finely divided particles of silver - the glass darkens. In the dark, the reverse process occurs (because free bromine is not able to leave the resulting cavities in the glass) and the glass becomes transparent again.

Toxicity

The solubility of silver bromide in water is small, so when consuming silver bromide orally, most of it is excreted in the feces. With systematic use, accumulation in the body and deposition of metallic silver in the illuminated areas of the body is possible, which is accompanied by the acquisition by the skin of a gray tint ( argyrosis ). In this case, no negative sensations are observed in patients, but it indicates the best resistance of the body to diseases, which confirms the bactericidal properties of silver.

Notes

↑ ¹ ² Levinson-Lessing F. Yu. Bromite or Bromargyrite // Encyclopedic Dictionary of Brockhaus and Efron : 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.

[Викитека_ЭСБЕ-1] ¹ ² Levinson-Lessing F. Yu. Bromite or Bromargyrite // Encyclopedic Dictionary of Brockhaus and Efron : 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.