Editing Devarda's alloy

{{Chembox
| ImageFile1 = File:Devarda's alloy.ვკ.jpg
|Section1={{Chembox Identifiers
| CASNo = 8049-11-4
| ChemSpiderID = none
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = GSX651880X 
| PubChem = 16211762
}}
|Section2={{Chembox Properties
| Formula = <!-- nicht angebbar, da Stoffgemisch. Aus der Zusammensetzung 45% Al, 50% Cu und 5% Zn (Massenprozente) ergibt sich eine [[Verhältnisformel]] von Al<sub>21,8</sub>Cu<sub>10,3</sub>Zn oder gerundet ungefähr Al<sub>22</sub>Cu<sub>10</sub>Zn. //-->
| Density = 5.79 g/cm<sup>3</sup><!-- <ref name="merck" /> -->
| MeltingPtC = 490 to 560
| MeltingPt_ref = <ref>{{cite web|title=SICHERHEITSDATENBLATT|url=http://www.merckmillipore.com/INTERSHOP/web/WFS/Merck-DE-Site/de_DE/-/EUR/ShowDocument-File?ProductSKU=MDA_CHEM-105341&DocumentId=105341_SDS_DE_DE.PDF&DocumentType=MSD&Language=DE&Country=DE|website=Merck}}</ref> 
| BoilingPtC = 906
| BoilingPt_ref =
| Solubility = insoluble 
  }}
|Section7={{Chembox Hazards
| GHSPictograms = {{GHS02}}
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|228}}
| PPhrases = {{P-phrases|210|240|241|280|378}}
}}
}}

'''Devarda's alloy''' (CAS # 8049-11-4) is an [[alloy]] of [[aluminium]] (44%&nbsp;–&nbsp;46%), [[copper]] (49%&nbsp;–&nbsp;51%) and [[zinc]] (4%&nbsp;–&nbsp;6%).

Devarda's alloy is used as [[reducing agent]] in [[analytical chemistry]] for the determination of [[nitrate]]s after their reduction to [[ammonia]] under alkaline conditions. It is named for Italian chemist [[Arturo Devarda]] (1859–1944), who synthesised it at the end of the 19th century to develop a new method to analyze [[nitrate]] in [[Sodium nitrate|Chile saltpeter]].<ref>{{Cite journal |last=Devarda |first=A. |year=1892 |title=Ueber die direkte bestimmung des stickstoffs im salpeter |trans-title=On the direct determination of nitrogen in saltpetre |journal=Chemiker Zeitung |language=de |volume=16 |pages=1952}}</ref><ref>{{Cite journal |last=Devarda |first=A. |year=1894 |title=Eine neue methode zur bestimmung des stickstoffs im chilisalpeter |trans-title=A new method for the determination of nitrogen in Chile saltpetre |url=https://zenodo.org/record/1428194 |journal=Zeitschrift für analytische Chemie |language=de |volume=33 |issue=1 |pages=113–114 |doi=10.1007/bf01335775 |s2cid=97552792}}</ref><ref>{{Cite journal |last1=Devarda |first1=A. |last2=Fields |first2=J. |year=1899 |title=Ueber stickstoffbestimmung |trans-title=On nitrogen determination |url=https://zenodo.org/record/1447427 |journal=Zeitschrift für analytische Chemie |language=de |volume=38 |issue=1 |pages=55–57 |doi=10.1007/bf01386922 |s2cid=197597366}}</ref>

It was often used in the quantitative or qualitative analysis of [[nitrate]]s in agriculture and soil science before the development of [[ion chromatography]], the predominant analysis method largely adopted worldwide today.<ref>{{Cite journal
| last = Feigl
| first = Fritz
| year = 1961
| title = Spot tests based on redox reactions with Devarda's alloy and Raney alloy
| journal = Analytical Chemistry
| volume = 33
| issue = 8
| pages = 1118–1121
| doi = 10.1021/ac60176a018
}}</ref><ref>{{Cite journal
| last = O'Deen
| first = William A.
| author2 =Lynn K. Porter
| year = 1980
| title = Devarda's alloy reduction of nitrate and tube diffusion of the reduced nitrogen for indophenol ammonium and nitrogen-15 determinations
| journal = Analytical Chemistry
| volume = 52
| issue = 7
| pages = 1164–1166
| doi = 10.1021/ac50057a044
}}</ref>

==General mechanism==
When a solution of nitrate ions is mixed with [[water|aqueous]] [[sodium hydroxide]], adding Devarda's alloy and heating the mixture gently, liberates [[ammonia]] [[gas]]. After conversion under the form of ammonia, the total nitrogen is then determined by [[Kjeldahl method]].<ref>{{Cite journal
| doi = 10.2136/sssaj1981.03615995004500050005x
| last = Liao
| first = Christina F.H.
| year = 1981
| title = Devarda's alloy method for total nitrogen determination
| journal = [[Soil Science Society of America Journal]]
| volume = 45
| issue = 5
| pages = 852–855
| bibcode = 1981SSASJ..45..852L
}}</ref>

The [[chemical reaction|reduction]] of nitrate by the Devarda's alloy is given by the following [[ionic equation|equation]]:

:3 {{chem|NO|3|-}} + 8 Al + 5 {{chem|OH|-}} + 18 {{chem|H|2|O}} → 3 {{chem|NH|3}} + 8 {{chem|[Al(OH)|4|]|-}}

==Distinction between NO<sub>3</sub><sup>−</sup> and NO<sub>2</sub><sup>−</sup> with spot tests==
To distinguish between [[nitrate]] and [[nitrite]], dilute HCl must be added to the nitrate. The [[nitrate test|brown ring test]] can also be used.

==Similarity with the Marsh test==
{{main|Marsh test}}
Devarda's alloy is a [[reducing agent]] that was commonly used in wet [[analytical chemistry]] to produce so-called [[nascent hydrogen]] under alkaline conditions ''in situ''. In the [[Marsh test]], used for arsenic determination, hydrogen is generated by contacting [[zinc]] powder with [[hydrochloric acid]]. So, hydrogen can be conveniently produced at low or high pH, according to the volatility of the species to be detected. Acid conditions in the Marsh test promote the fast escape of the [[arsine]] gas (AsH<sub>3</sub>), while in hyperalkaline solution, the degassing of the reduced [[ammonia]] (NH<sub>3</sub>) is greatly facilitated.

==Long-debated question of the nascent hydrogen==
{{main|Nascent hydrogen}}
Since the mid-19th century the existence of true [[nascent hydrogen]] has repeatedly been challenged. It was assumed by the supporters of this theory that, before two hydrogen atoms can recombine into a more stable H<sub>2</sub> molecule, the labile H· free radicals are more reactive than molecular H<sub>2</sub>, a relatively weak [[reductant]] in the absence of a metal catalyst. Nascent hydrogen was supposed to be responsible for the reduction of arsenate or nitrate in [[arsine]] or [[ammonia]] respectively. Nowadays, isotopic evidence<ref>{{Cite journal
| last1=Laborda 
| first1=F. 
| first2=E. |last2=Bolea 
| first3=M. T. |last3=Baranguan 
| first4=J. R. |last4=Castillo 
| year = 2002
| title = Hydride generation in analytical chemistry and nascent hydrogen: when is it going to be over?
| journal = Spectrochimica Acta Part B: Atomic Spectroscopy
| volume = 57
| issue = 4
| pages = 797–802
| doi = 10.1016/S0584-8547(02)00010-1
| issn = 0584-8547
| bibcode = 2002AcSpB..57..797L }}</ref> has closed the nascent hydrogen debate, presently considered to be a ''[[Gedanken]]'' artifact of romanticism.<ref>{{Cite journal
| last = Tommasi
| first = D.
| year = 1897
| title = Comment on the Note of R. Franchot entitled "Nascent Hydrogen"
| journal = The Journal of Physical Chemistry
| volume = 1
| issue = 9
| pages = 555
| doi = 10.1021/j150591a004
| issn = 1618-2642
| url = https://zenodo.org/record/1428786
}}</ref><ref>{{Cite journal
| last1=Meija |first1=Juris 
| last2=D’Ulivo |first2=Alessandro 
| year = 2008
| title = Nascent hydrogen challenge
| journal = Analytical and Bioanalytical Chemistry
| volume = 391
| issue = 5
| pages = 1475–6
| doi = 10.1007/s00216-008-2143-4
| issn = 1618-2642
| pmid = 18488209
|s2cid=19542514 
}}</ref><ref>{{Cite journal
| last1=Meija |first1=Juris 
| last2=D’Ulivo |first2=Alessandro 
| year = 2008
| title = Solution to nascent hydrogen challenge
| journal = Analytical and Bioanalytical Chemistry
| volume = 392
| issue = 5
| pages = 771–772
| doi = 10.1007/s00216-008-2356-6
| issn = 1618-2642
| pmid = 18795271
|s2cid=206900604 
}}</ref>

==See also==
* [[Kjeldahl method]]
* [[Nitrate test]]
* [[Nitrite test]]
* [[Nascent hydrogen]]
* [[Marsh test]]
* Detection of:
** [[Arsine]]
** [[Stibine]]
* [[Raney nickel]], prepared from an Al, Ni alloy also dissolved in concentrated [[NaOH]]
* [[Zinc-copper couple]]

==References==
{{reflist|30em}}

==External links==
* [https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?sid=24856330 Devarda's alloy - Substance Summary  (SID 24856330)] ([[PubChem|PubChem Substance]])
* [http://msds.chem.ox.ac.uk/DE/devarda%27s_alloy.html Safety data for Devarda's alloy]{{Dead link|date=April 2024 |bot=InternetArchiveBot |fix-attempted=yes }}
* [http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=81966|FLUKA&N5=SEARCH_CONCAT_PNO|BRAND_KEY&F=SPEC Sigma Aldrich: Devarda’s alloy purum, for preparative purposes, grit]
* [https://web.archive.org/web/20100325131239/http://www.gfschemicals.com/statics/productdetails/DEVARDA_S_ALLOY_5399.html GFS Chemicals: Devarda's alloy, reagent (ACS)]
* [https://web.archive.org/web/20080302034606/http://www.npi.gov.au/database/substance-info/profiles/27.html National Pollutant Inventory - Copper and compounds fact sheet]

==Further reading==
* {{Cite journal
| last = Cahen
| first = Edward
| year = 1910
| title = A comparison of Pozzi-Escot's and Devarda's method for the estimation of nitrates
| journal = The Analyst
| volume = 35
| issue = 412
| pages = 307–308
| doi = 10.1039/AN9103500307
| bibcode = 1910Ana....35..307C }}
* {{Cite journal
| last = Kieselbach
| first = Richard
| year = 1944
| title = Microdetermination of nitrates by Devarda method
| journal = Industrial & Engineering Chemistry Analytical Edition
| volume = 16
| issue = 12
| pages = 764–766
| doi = 10.1021/i560136a017
}}
{{aluminium alloys}}

[[Category:Aluminium alloys]]
[[Category:Copper alloys]]
[[Category:Name reactions]]
[[Category:Hydrogen]]
[[Category:Reducing agents]]
[[Category:Aluminium–copper alloys]]