Zinc chloride
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| Structure of α-zinc chloride: __ Zn 2+ __ Cl - |
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| General | ||||||||||||||||
| Surname | Zinc chloride | |||||||||||||||
| other names |
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| Ratio formula | ZnCl 2 | |||||||||||||||
| Brief description |
white, granular powder made of hexagonal-rhombohedral flakes |
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| properties | ||||||||||||||||
| Molar mass | 136.29 g · mol -1 | |||||||||||||||
| Physical state |
firmly |
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| density |
2.91 g cm −3 (25 ° C) |
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| Melting point |
290 ° C |
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| boiling point |
732 ° C |
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| solubility | ||||||||||||||||
| safety instructions | ||||||||||||||||
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| MAK |
Switzerland: 1 mg m −3 (measured as respirable dust ) |
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| Toxicological data | ||||||||||||||||
| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | ||||||||||||||||
Zinc chloride (ZnCl 2 ) is a white, granular powder that is formed when zinc is heated in chlorine or zinc sulfate with calcium chloride , also when zinc, zinc oxide or zinc blende react with hydrochloric acid .
history
Zinc chloride was presented in 1648 by Johann Rudolph Glauber from Galmei and in 1741 by Johann Heinrich Pott from zinc.
Extraction and presentation
To produce pure zinc chloride, zinc is reacted with hydrochloric acid, whereby the metal must ultimately be present in excess, the solution is treated with chlorine to convert impurities from iron into iron (III) chloride (FeCl 3 ), then the iron hydroxide falls through Digest with zinc oxide, filter and evaporate until a drop solidifies on a cold porcelain plate.
With stronger evaporation hydrochloric acid escapes, and the preparation then gives a cloudy solution due to the formation of basic zinc chlorides, complex compositions. If it is evaporated to dryness, a sublimate of anhydrous zinc chloride is obtained if the temperature is increased.
On a large scale, zinc chloride is obtained by reacting zinc furnace fragments (zinc oxide) with hydrochloric acid, by treating zinc blende with hydrochloric acid, whereby the escaping hydrogen sulfide gas (H 2 S) is used for the production of sulfuric acid, and also by leaching roasted glare-containing sulfur pebbles.
properties
Anhydrous zinc chloride is whitish, translucent (zinc butter), melts at over 318 ° C, distills in red heat, is very hygroscopic and very easily soluble in ethanol . The solution becomes syrupy on evaporation and, with a little hydrochloric acid added, gives colorless, very deliquescent crystals with one molecule of water.
Zinc chloride has a burning taste, has a strong corrosive effect , dissolves plant fibers , removes water from many organic substances - in the same way as concentrated sulfuric acid - carbonizes wood, for example, converts alcohol into ether (ether), paper into parchment paper, etc.
use
To use zinc chloride for the impregnation of wood , for the preservation of animal substances in the refining of oil , in the preparation of parchment paper, vulcanized fiber , ether , stearic acid ; With chlorinated lime for bleaching the paper, in dyeing as a stain for aniline blue , for the representation of some tar colors and garancin , for staining and dyeing the brass , for gluing the paper pulp , for disinfecting, in chemical work as a dehydrating agent, in medicine as a caustic agent , a concentrated solution for heating vessels evenly to a certain higher temperature.
A solution of syrupy zinc chloride, mixed with zinc oxide, solidifies and gives a white, very hard mass consisting of basic zinc chloride, which can be used as tooth and metal putty, especially if you add a little glass powder. Paints in which zinc oxychloride forms have also been recommended.
For example, 4 liters of acid-free zinc chloride solution of 58 ° Bé (corresponding to a density of 1.74 g / cm 3 ) are mixed with 10 liters of a solution containing 2% carbonate of soda, and zinc oxide is added to the appropriate consistency. This odorless and cheap mixture must be consumed immediately. The paint is permanent, but does not tolerate any coloring additives. A solution of zinc chloride with a specific gravity of 1.7, boiled with excess zinc oxide, dissolves silk.
Soldering fluid and soldering salt
Ammonium zinc chloride (NH 4 ) 2 [ZnCl 4 ] ( soldering salt ) crystallizes from mixed, very concentrated solutions of zinc chloride and salmia or from a solution of zinc oxide or zinc hydroxide in salmia . A solution of zinc in concentrated hydrochloric acid, which contains as much ammonia as zinc ( soldering water ), removes the oxides from a piece of metal (copper, iron) before it is soldered or tinned .
Alternatively, an approximately 30% solution of zinc chloride in water acidified with a little hydrochloric acid with the addition of a little ammonium chloride can be used as soldering water. It is used in technology as a wetting and surface activating agent for tinning at around 300 ° C. The zinc chloride is able, especially in the heat on the surfaces such. B. to dissolve oxides (Fe 2 O 3 ) found in steel by complex formation, to dissipate them from the steel surface and, after tinning, to enable direct contact between steel and tin: A firm bond is created between steel and tin.
In smoke or smoke, zinc chloride is produced in finely divided form by burning a mixture of zinc oxide , hexachloroethane and powdered aluminum . In addition to zinc chloride, the smoke produced in this way also contains hydrochloric acid and other organochlorine compounds .
proof
Sodium hydroxide solution (NaOH) with zinc chloride results in a gelatinous precipitate of zinc hydroxide Zn (OH) 2 , which dissolves again in excess of the precipitant to form the tetrahedral, complex tetrahydroxidozincate (II) [Zn (OH) 4 ] 2− . With ammonia solution instead of sodium hydroxide solution, the hydroxide initially formed dissolves to form the tetrammine complex.
If silver nitrate is added to a solution of zinc chloride, a white precipitate of silver chloride forms :
From a hydrochloric acid, acetate-buffered solution, the zinc with potassium hexacyanidoferrate (II) precipitates as a slightly soluble, whitish precipitate:
![{\ mathrm {3 \ Zn ^ {{2 +}} + 2 \ K_ {4} [Fe (CN) _ {6}] \ longrightarrow 6 \ K ^ {+} + K_ {2} Zn_ {3} [ Fe (CN) _ {6}] _ {2} \ downarrow}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/0b032b12065b94674d6430631701c743541c5715)
Zinc can also be detected as Rinman's green .
Web links
Individual evidence
- ↑ a b entry on zinc chloride. In: Römpp Online . Georg Thieme Verlag, accessed on September 29, 2014.
- ↑ a b c d e f Entry on zinc chloride in the GESTIS substance database of the IFA , accessed on February 1, 2016(JavaScript required) .
- ↑ Entry on Zinc chloride in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
- ↑ Swiss Accident Insurance Fund (Suva): Limit values - current MAK and BAT values (search for 7646-85-7 or zinc chloride ), accessed on November 2, 2015.
- ↑ Zinc chloride data sheet (PDF) from Merck , accessed on January 19, 2011.
- ^ H. Brill .: trade sheet for the Grand Duchy of Hesse. H. Brill., 1890, p. 21 ( limited preview in Google book search).
- ↑ a b c d Jander, Blasius: Introduction to the inorganic-chemical practical course , 14th edition 1995