Devarda's alloy
Encyclopedia
Devarda's alloy 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 nitrate
s after their reduction to ammonia
under alkaline conditions. It owes its name to the Italian chemist Arturo Devarda (1859–1944), who synthezised 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 nitrate
s in agriculture and soil science before the development of ion chromatography, the predominant analysis method largely adopted worldwide today.
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:
and nitrite
dilute HCl must be added to the nitrate. The Brown Ring Test
can also be used.
that was commonly used in wet analytical chemistry
to produce in situ the so-called nascent hydrogen
in alkaline conditions. 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.
was repeatedly challenged. It was assumed by the supporters of this theory that before that 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 metal catalyst. Nascent hydrogen was supposed to be responsible of the reduction of arsenate or nitrate in arsine
or ammonia
respectively. Nowadays, isotopic evidences have closed the nascent hydrogen debate, presently considered as a Gedanken artifact of romanticism.
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
of aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
(44% – 46%), copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
(49% – 51%) and zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
(4% – 6%).
Devarda's alloy is used as reducing agent
Reducing agent
A reducing agent is the element or compound in a reduction-oxidation reaction that donates an electron to another species; however, since the reducer loses an electron we say it is "oxidized"...
in analytical chemistry
Analytical chemistry
Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of...
for the determination of nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
s after their reduction to ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
under alkaline conditions. It owes its name to the Italian chemist Arturo Devarda (1859–1944), who synthezised it at the end of the 19th century to develop a new method to analyze nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
in Chile saltpeter
Sodium nitrate
Sodium nitrate is the chemical compound with the formula NaNO3. This salt, also known as Chile saltpeter or Peru saltpeter to distinguish it from ordinary saltpeter, potassium nitrate, is a white solid which is very soluble in water...
.
It was often used in the quantitative or qualitative analysis of nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
s in agriculture and soil science before the development of ion chromatography, the predominant analysis method largely adopted worldwide today.
General mechanism
When a solution of nitrate ions is mixed with aqueousWater
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
sodium hydroxide, adding Devarda's alloy and heating the mixture gently, liberates ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
. After conversion under the form of ammonia, the total nitrogen is then determined by Kjeldahl method
Kjeldahl method
The Kjeldahl method or Kjeldahl digestion in analytical chemistry is a method for the quantitative determination of nitrogen in chemical substances developed by Johan Kjeldahl in 1883.- Method :...
.
The reduction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
of nitrate by the Devarda's alloy is given by the following equation:
- 3 + 8 Al + 5 + 18 → 3 + 8
Distinction between NO3− and NO2− with spot tests
To distinguish between nitrateNitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
and nitrite
Nitrite
The nitrite ion has the chemical formula NO2−. The anion is symmetric with equal N-O bond lengths and a O-N-O bond angle of ca. 120°. On protonation the unstable weak acid nitrous acid is produced. Nitrite can be oxidised or reduced, with product somewhat dependent on the oxidizing/reducing agent...
dilute HCl must be added to the nitrate. The Brown Ring Test
Nitrate test
A nitrate test is a chemical test used to determine the presence of nitrate ion in solution. Testing for the presence of nitrate via wet chemistry is generally difficult compared with testing for other anions, as almost all nitrates are soluble in water. In contrast, many common ions give insoluble...
can also be used.
Similarity with the Marsh test
The Devarda's alloy is a reducing agentReducing agent
A reducing agent is the element or compound in a reduction-oxidation reaction that donates an electron to another species; however, since the reducer loses an electron we say it is "oxidized"...
that was commonly used in wet analytical chemistry
Analytical chemistry
Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of...
to produce in situ the so-called nascent hydrogen
Nascent hydrogen
Atomic hydrogen is the species denoted by H , contrasted with dihydrogen, the usual 'hydrogen' commonly involved in chemical reactions. It is claimed to exist transiently but long enough to effect chemical reactions...
in alkaline conditions. In the Marsh test
Marsh test
The Marsh test is a highly sensitive method in the detection of arsenic, especially useful in the field of forensic toxicology when arsenic was used as a poison...
, used for arsenic determination, hydrogen is generated by contacting zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
powder with hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric 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
Arsine
Arsine is the chemical compound with the formula AsH3. This flammable, pyrophoric, and highly toxic gas is one of the simplest compounds of arsenic...
gas (AsH3), while in hyperalkaline solution, the degassing of the reduced ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
(NH3) is greatly facilitated.
Long-debated question of the nascent hydrogen
Since the mid-19th century the existence of true nascent hydrogenNascent hydrogen
Atomic hydrogen is the species denoted by H , contrasted with dihydrogen, the usual 'hydrogen' commonly involved in chemical reactions. It is claimed to exist transiently but long enough to effect chemical reactions...
was repeatedly challenged. It was assumed by the supporters of this theory that before that 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 metal catalyst. Nascent hydrogen was supposed to be responsible of the reduction of arsenate or nitrate in arsine
Arsine
Arsine is the chemical compound with the formula AsH3. This flammable, pyrophoric, and highly toxic gas is one of the simplest compounds of arsenic...
or ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
respectively. Nowadays, isotopic evidences have closed the nascent hydrogen debate, presently considered as a Gedanken artifact of romanticism.
See also
- Kjeldahl methodKjeldahl methodThe Kjeldahl method or Kjeldahl digestion in analytical chemistry is a method for the quantitative determination of nitrogen in chemical substances developed by Johan Kjeldahl in 1883.- Method :...
- Nitrate testNitrate testA nitrate test is a chemical test used to determine the presence of nitrate ion in solution. Testing for the presence of nitrate via wet chemistry is generally difficult compared with testing for other anions, as almost all nitrates are soluble in water. In contrast, many common ions give insoluble...
- Nitrite testNitrite testA nitrite test is a chemical test used to determine the presence of nitrite ion in solution.-Chemical method:A common nitrite test can be performed by adding 4 M sulfuric acid to the sample until acidic, and then adding 0.1 M iron sulfate to the solution...
- Nascent hydrogenNascent hydrogenAtomic hydrogen is the species denoted by H , contrasted with dihydrogen, the usual 'hydrogen' commonly involved in chemical reactions. It is claimed to exist transiently but long enough to effect chemical reactions...
- Marsh testMarsh testThe Marsh test is a highly sensitive method in the detection of arsenic, especially useful in the field of forensic toxicology when arsenic was used as a poison...
- Detection of:
- ArsineArsineArsine is the chemical compound with the formula AsH3. This flammable, pyrophoric, and highly toxic gas is one of the simplest compounds of arsenic...
- StibineStibineStibine is the chemical compound with the formula SbH3. This colourless gas is the principal covalent hydride of antimony and a heavy analogue of ammonia. The molecule is pyramidal with H–Sb–H angles of 91.7° and Sb–H distances of 1.707 Å...
- Arsine
- Raney nickelRaney nickelRaney nickel is a solid catalyst composed of fine grains of a nickel-aluminium alloy, used in many industrial processes. It was developed in 1926 by American]] engineer Murray Raney as an alternative catalyst for the hydrogenation of vegetable oils in industrial processes...
, prepared from an Al, Ni alloy also dissolved in concentrated NaOH
External links
- http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?sid=24856330Devarda's alloy - Substance Summary (SID 24856330) (PubChem SubstancePubChemPubChem is a database of chemical molecules and their activities against biological assays. The system is maintained by the National Center for Biotechnology Information , a component of the National Library of Medicine, which is part of the United States National Institutes of Health . PubChem can...
)] - Safety data for Devarda's alloy
- Sigma Aldrich: Devarda’s alloy purum, for preparative purposes, grit
- GFS Chemicals: Devarda's alloy, reagent (ACS)
- National Pollutant Inventory - Copper and compounds fact sheet