Devarda's alloy

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Devarda's alloy
Identifiers
ChemSpider
  • none
ECHA InfoCard
 100.209.703 Edit this at Wikidata
UNII
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)
insoluble
Hazards
GHS labelling:
GHS02: Flammable
Warning
H228
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).

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

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

Main article: 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

Main article: Nascent hydrogen

Since the mid-19th century the existence of true

Gedanken artifact of romanticism.[9][10][11]

See also

References

  1. ^ "SICHERHEITSDATENBLATT". Merck.
  2. ^ Devarda, A. (1892). "Ueber die direkte bestimmung des stickstoffs im salpeter". Chemiker Zeitung. 16: 1952.
  3. S2CID 97552792
    .
  4. S2CID 197597366
    .
  5. doi:10.1021/ac60176a018
    .
  6. doi:10.1021/ac50057a044
    .
  7. doi:10.2136/sssaj1981.03615995004500050005x
    .
  8. ISSN 0584-8547
    .
  9. ISSN 1618-2642
    .
  10. S2CID 19542514
    .
  11. S2CID 206900604
    .

External links

Further reading

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