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Devarda's alloy - Wikipedia

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Devarda's alloy
Identifiers

CAS Number	8049-11-4
ChemSpider	none
ECHA InfoCard	100.209.703
PubChem CID	16211762
UNII	GSX651880X^Y
CompTox Dashboard (EPA)	DTXSID50583479
Properties
Density	5.79 g/cm³
Melting point	490 to 560 °C (914 to 1,040 °F; 763 to 833 K)^[1]
Boiling point	906 °C (1,663 °F; 1,179 K)
Solubility in water	insoluble
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H228
Precautionary statements	P210, P240, P241, P280, P378
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

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

Devarda's alloy is used as reducing agent in analytical chemistry for the determination of nitrates 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 Chile saltpeter.^[2]^[3]^[4]

It was often used in the quantitative or qualitative analysis of nitrates in agriculture and soil science before the development of ion chromatography, the predominant analysis method largely adopted worldwide today.^[5]^[6]

General mechanism

When a solution of nitrate ions is mixed with 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.^[7]

The reduction of nitrate by the Devarda's alloy is given by the following equation:

3 NO⁻
₃ + 8 Al + 5 OH⁻
+ 18 H
₂O → 3 NH
₃ + 8 [Al(OH)
₄]⁻

Distinction between NO₃⁻ and NO₂⁻ with spot tests

To distinguish between nitrate and nitrite, dilute HCl must be added to the nitrate. The brown ring test can also be used.

Similarity with the 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 (AsH₃), while in hyperalkaline solution, the degassing of the reduced ammonia (NH₃) is greatly facilitated.

Long-debated question of the 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 H₂ molecule, the labile H· free radicals are more reactive than molecular H₂, 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^[8] has closed the nascent hydrogen debate, presently considered to be a Gedanken artifact of romanticism.^[9]^[10]^[11]

References

^ "SICHERHEITSDATENBLATT". Merck.
^ Devarda, A. (1892). "Ueber die direkte bestimmung des stickstoffs im salpeter" [On the direct determination of nitrogen in saltpetre]. Chemiker Zeitung (in German). 16: 1952.
^ Devarda, A. (1894). "Eine neue methode zur bestimmung des stickstoffs im chilisalpeter" [A new method for the determination of nitrogen in Chile saltpetre]. Zeitschrift für analytische Chemie (in German). 33 (1): 113–114. doi:10.1007/bf01335775. S2CID 97552792.
^ Devarda, A.; Fields, J. (1899). "Ueber stickstoffbestimmung" [On nitrogen determination]. Zeitschrift für analytische Chemie (in German). 38 (1): 55–57. doi:10.1007/bf01386922. S2CID 197597366.
^ Feigl, Fritz (1961). "Spot tests based on redox reactions with Devarda's alloy and Raney alloy". Analytical Chemistry. 33 (8): 1118–1121. doi:10.1021/ac60176a018.
^ O'Deen, William A.; Lynn K. Porter (1980). "Devarda's alloy reduction of nitrate and tube diffusion of the reduced nitrogen for indophenol ammonium and nitrogen-15 determinations". Analytical Chemistry. 52 (7): 1164–1166. doi:10.1021/ac50057a044.
^ Liao, Christina F.H. (1981). "Devarda's alloy method for total nitrogen determination". Soil Science Society of America Journal. 45 (5): 852–855. Bibcode:1981SSASJ..45..852L. doi:10.2136/sssaj1981.03615995004500050005x.
^ Laborda, F.; Bolea, E.; Baranguan, M. T.; Castillo, J. R. (2002). "Hydride generation in analytical chemistry and nascent hydrogen: when is it going to be over?". Spectrochimica Acta Part B: Atomic Spectroscopy. 57 (4): 797–802. Bibcode:2002AcSpB..57..797L. doi:10.1016/S0584-8547(02)00010-1. ISSN 0584-8547.
^ Tommasi, D. (1897). "Comment on the Note of R. Franchot entitled "Nascent Hydrogen"". The Journal of Physical Chemistry. 1 (9): 555. doi:10.1021/j150591a004. ISSN 1618-2642.
^ Meija, Juris; D’Ulivo, Alessandro (2008). "Nascent hydrogen challenge". Analytical and Bioanalytical Chemistry. 391 (5): 1475–6. doi:10.1007/s00216-008-2143-4. ISSN 1618-2642. PMID 18488209. S2CID 19542514.
^ Meija, Juris; D’Ulivo, Alessandro (2008). "Solution to nascent hydrogen challenge". Analytical and Bioanalytical Chemistry. 392 (5): 771–772. doi:10.1007/s00216-008-2356-6. ISSN 1618-2642. PMID 18795271. S2CID 206900604.

External links

Cahen, Edward (1910). "A comparison of Pozzi-Escot's and Devarda's method for the estimation of nitrates". The Analyst. 35 (412): 307–308. Bibcode:1910Ana....35..307C. doi:10.1039/AN9103500307.
Kieselbach, Richard (1944). "Microdetermination of nitrates by Devarda method". Industrial & Engineering Chemistry Analytical Edition. 16 (12): 764–766. doi:10.1021/i560136a017.

v t e Aluminium alloys
Introduction	Aluminium Aluminum powder Aluminium alloys History of aluminium
Al 1000 series (pure)	1050 1060 1070 1100 1145 1199 1200 1230 1350 1370 1420 1421 1424 1430 1440 1441 1445 1450 1460 1461 1464 1469
Al-Cu 2000 series	2004 2011 2014 2017 2020 2024 2025 2029 2036 2048 2055 2080 2090 2091 2094 2095 2097 2098 2099 2124 2195 2196 2197 2198 2218 2219 2224&2324 2297 2319 2397 2519 2524 2618
Al-Mn 3000 series	3003 3004 3005 3102 3102&3303 3105 3203
Al-Si 4000 series	4006 4007 4015 4032 4043 4047 4543
Al-Mg 5000 series	5005&5657 5010 5019 5024 5026 5050 5052&5652 5056 5059 5083 5086 5154&5254 5182 5252 5356 5454 5456 5457 5557 5754
Al-Mg-Si 6000 series	6005 (6005A) 6009 6010 6013 6022 6060 6061 6063 6065 6066 6070 6081 6082 6101 6105 6113 6151 6162 6201 6205 6262 6351 6463 6951
Al-Zn 7000 series	7005 7010 7022 7034 7039 7046 7050 7055 7065 7068 7072 7075 7079 7085 7090 7091 7093 7116 7129 7150 7178 7255 7475
8000 series (misc.)	8006 8009 8011 8014 8019 8025 8030 8090 8091 8093 8176
Named alloys	Aluminium–lithium alloys AlBeMet Alclad Alnico AlSiC Alumel Aluminium granules Alusil Birmabright Devarda's alloy Duralumin Hiduminium (aka R.R. alloys) Hydronalium Italma Lo-Ex Magnalium Magnox (alloy) MKM steel Nickel aluminide Aluminium–scandium alloys Y alloy Al-Ca composite Hypereutectic piston Aluminium bronze AlSi10Mg

General mechanism

Distinction between NO₃⁻ and NO₂⁻ with spot tests

Similarity with the Marsh test

Long-debated question of the nascent hydrogen

See also

References

External links

Further reading

General mechanism

Distinction between NO3− and NO2− with spot tests

Similarity with the Marsh test

Long-debated question of the nascent hydrogen

See also

References

External links

Further reading

Distinction between NO₃⁻ and NO₂⁻ with spot tests