Devarda's alloy
| Identifiers | |
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| ChemSpider |
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| ECHA InfoCard | 100.209.703 |
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| Properties | |
| Density | 5,79 g·cm−3 |
| Melting point | 490 to 560 °C (914 to 1,040 °F; 763 to 833 K) |
| Boiling point | 906 °C (1,663 °F; 1,179 K) |
| insoluble | |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| 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 owes its name to the 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.
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.
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.
The reduction of nitrate by the Devarda's alloy is given by the following equation:
To distinguish between nitrate and nitrite dilute HCl must be added to the nitrate. The Brown Ring Test can also be used.
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 volatily 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.
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