Silver chloride

Crystal structure
	__ Ag + __ Cl -
Crystal system	cubic
Space group	Fm 3 m (No. 225)
Lattice parameters	a = 554.91 pm
Coordination numbers	Ag [6], Cl [6]
General
Surname	Silver chloride
other names	Silver (I) chloride; Chlorine silver; Horn silver;
Ratio formula	AgCl
Brief description	colorless crystals, powder appears white
External identifiers / databases
EC number	232-033-3
ECHA InfoCard	100.029.121
PubChem	24561
Wikidata	Q216918
properties
Molar mass	143.32 g mol −1
Physical state	firmly
density	5.56 g cm −3
Melting point	455 ° C
boiling point	1550 ° C
Vapor pressure	1.3 h Pa (912 ° C)
solubility	practically insoluble in water (1.88 mg l −1 at 25 ° C)
Dipole moment	6.08 (6) D (2.0 · 10 −29 C · m )
Refractive index	2.0668
safety instructions
H and P phrases	H: 290-410
	P: 273-390-501
MAK	0.01 mg m −3
Toxicological data	> 5110 mg kg −1 ( LD 50 , mouse , oral )
Thermodynamic properties
ΔH f 0	−127.01 (5) kJ / mol
	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

Silver chloride [also: silver (I) chloride] can be regarded as the silver salt of hydrochloric acid (HCl); As a noble metal , however, silver does not dissolve in hydrochloric acid; instead, silver chloride is formed from water-soluble silver compounds such as silver nitrate and chloride ions.

properties

Silver chloride

Silver chloride
with and without ammonia water

Silver chloride is a white, microcrystalline, light-sensitive substance with a melting point of 455 ° C and a boiling point of 1550 ° C. Silver chloride is sparingly soluble in water as in nitric acid. Its solubility product is 2 ∙ 10 ⁻¹⁰ mol ² / l ² . However, it dissolves very easily with complex formation in ammonia , sodium thiosulphate and potassium cyanide solutions . This forms [Ag (NH ₃ ) ₂ ] ⁺ , [Ag (S ₂ O ₃ ) ₂ ] ³⁻ and [Ag (CN) ₂ ] ^- . The crystal lattice of silver chloride (as well as that of silver fluoride AgF and silver bromide AgBr, but not silver iodide AgI) corresponds to the salt lattice .

Occurrence

Silver chloride occurs naturally as the mineral chlorargyrite .

use

Used for the long-term inactivation of bacteria in drinking water containers.

In the laboratory, the silver content of samples is determined by weight analysis (gravimetric) or dimensional analysis (titrimetric) due to the low solubility in water via the precipitation of silver chloride.

Silver halides are broken down by light into the corresponding elemental halogen and metallic silver. They are therefore used for the photosensitive layer of photographic films, plates and papers. Silver chloride is less sensitive to light than the chemically similar silver bromide AgBr, which is normally used for photography.

A use of silver chloride that is very important for electrochemistry is that in silver-silver chloride reference electrodes , since these are not polarizable and thus enable unadulterated measurements. Since mercury is increasingly being banned from the laboratory and technology, the calomel electrodes that were often used in the past are mostly replaced by Ag / AgCl electrodes, so that these are now used most frequently.

Such an electrode can be made by electrochemical oxidation of a silver wire in hydrochloric acid : For example, if two silver wires are immersed in hydrochloric acid and a voltage (1-2 V, 20-300 s) is applied, the anode (connected to the positive pole) is also connected Silver chloride covered

{\ displaystyle {\ begin {alignedat} {2} & {\ text {Oxidation:}} \ & 2 \; \ mathrm {Ag} +2 \; \ mathrm {HCl} & \ longrightarrow 2 \; \ mathrm {AgCl} +2 \; \ mathrm {H ^ {+}} +2 \; \ mathrm {e ^ {-}} \\ & {\ text {Reduction:}} \ & 2 \; \ mathrm {H ^ {+}} +2 \; \ mathrm {e ^ {-}} & \ longrightarrow \ mathrm {H_ {2}} \\\ hline & {\ text {Total:}} \ & 2 \; \ mathrm {Ag} +2 \; \ mathrm {HCl} & \ longrightarrow 2 \; \ mathrm {AgCl} + \ mathrm {H_ {2}} \ end {alignedat}}}

This process ensures that all silver chloride that is produced is in electrical contact with the electrode.

AgCl is on ECG - electrodes used as the electrolyte.

proof

In contrast to the silver halides AgBr and AgI, silver chloride dissolves in dilute ammonia solution to form a complex :

{\ displaystyle \ mathrm {AgCl + 2 \ NH_ {3} \ longrightarrow [Ag (NH_ {3}) _ {2}] ^ {+} + Cl ^ {-}}}

Silver chloride reacts with excess ammonia to form diammine silver (I) complex ions and chloride ions.

Analogous soluble complexes are also formed with cyanide or thiocyanate, so that silver chloride is dissolved. Silver chloride in concentrated hydrochloric acid to form the chloro complex [Cl-AgCl] ^- partially soluble, which is why you should use excess hydrochloric acid in the precipitation of AgCl no.

For example, insoluble silver salt can be excreted from the ammine complex with sulfide:

{\ displaystyle \ mathrm {2 \ [Ag (NH_ {3}) _ {2}] ^ {+} + S ^ {2 -} \ longrightarrow Ag_ {2} S + 4 \ NH_ {3}}}

Diammine silver (I) ions react with sulfide ions to form silver sulfide and ammonia.

Individual evidence

↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Crystallographic Data on Minerals, pp. 4-157.

↑ http://www.seilnacht.com/Lexikon/Chloride.htm

↑ ^a ^b ^c ^d ^e ^f ^g ^h Entry on silver chloride in the GESTIS substance database of the IFA , accessed on February 1, 2016 (JavaScript required)

↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Dipole Moments, pp. 9-52.

↑ 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. 10-245.

↑ Silver chloride data sheet (PDF) from Merck , accessed on January 19, 2011.

↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, CODATA Key Values for Thermodynamics, pp. 5-1.

↑ ^a ^b ^c ^d ^e ^f ^g Wiberg, Egon., Wiberg, Nils ,: Textbook of inorganic chemistry . 102nd, heavily reworked and verb. Ed. De Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 ( OCLC 180963521 ).

^ ^A ^b Jander, Gerhart, Blasius, Ewald: Jander / Blasius inorganic chemistry. 1 Introduction and qualitative analysis: with 21 formulas and 79 tables and poster "Pocket folder" . 17., completely reworked. Edition Hirzel, Stuttgart 2012, ISBN 3-7776-2134-X ( OCLC 844943271 ).

^ Chlorargyrite Mineral Data. Retrieved March 25, 2020 .

[CRC90_4_157-1] David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Crystallographic Data on Minerals, pp. 4-157.

[2] ttp://www.seilnacht.com/Lexikon/Chloride.htm

[GESTIS-3] ↑ ^a ^b ^c ^d ^e ^f ^g ^h Entry on silver chloride in the GESTIS substance database of the IFA , accessed on February 1, 2016 (JavaScript required)

[CRC90_9_52-4] David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Dipole Moments, pp. 9-52.

[CRC90_10_245-5] 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. 10-245.