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Devarda's alloy (CAS # 8049-11-4) is an
alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...
of
aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
(44% – 46%),
copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
(49% – 51%) and
zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...
(4% – 6%). Devarda's alloy is used as
reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are common reducing agents include hydrogen, carbon ...
in
analytical chemistry Analytical skill, Analytical chemistry studies and uses instruments and methods to Separation process, separate, identify, and Quantification (science), quantify matter. In practice, separation, identification or quantification may constitute t ...
for the determination of
nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...
s after their reduction to
ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
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 Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...
in Chile saltpeter. It was often used in the quantitative or qualitative analysis of
nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...
s in agriculture and soil science before the development of
ion chromatography Ion chromatography (or ion-exchange chromatography) is a form of chromatography that separates ions and ionizable polar molecules based on their affinity to the ion exchanger. It works on almost any kind of Charge (chemistry), charged molecule ...
, the predominant analysis method largely adopted worldwide today.


General mechanism

When a solution of nitrate ions is mixed with
aqueous An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, also known as sodium chloride (NaCl), in wat ...
sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base (chemistry), ...
, adding Devarda's alloy and heating the mixture gently, liberates
ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
gas Gas is a state of matter that has neither a fixed volume nor a fixed shape and is a compressible fluid. A ''pure gas'' is made up of individual atoms (e.g. a noble gas like neon) or molecules of either a single type of atom ( elements such as ...
. After conversion under the form of ammonia, the total nitrogen is then determined by
Kjeldahl method The Kjeldahl method or Kjeldahl digestion () in analytical chemistry is a method for the quantitative determination of a sample's organic compound, organic nitrogen plus ammonia/ammonium (NH3/NH4+). Without modification, other forms of inorganic ni ...
. The reduction of nitrate by the Devarda's alloy is given by the following
equation In mathematics, an equation is a mathematical formula that expresses the equality of two expressions, by connecting them with the equals sign . The word ''equation'' and its cognates in other languages may have subtly different meanings; for ...
: :3 + 8 Al + 5 + 18 → 3 + 8


Distinction between NO3− and NO2− with spot tests

To distinguish between
nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...
and
nitrite The nitrite polyatomic ion, ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name ...
, 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 In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are common reducing agents include hydrogen, carbon ...
that was commonly used in wet
analytical chemistry Analytical skill, Analytical chemistry studies and uses instruments and methods to Separation process, separate, identify, and Quantification (science), quantify matter. In practice, separation, identification or quantification may constitute t ...
to produce so-called
nascent hydrogen Nascent hydrogen is an outdated concept in organic chemistry that was once invoked to explain dissolving-metal reactions, such as the Clemmensen reduction and the Bouveault–Blanc reduction. Since organic compounds do not react with H2, a specia ...
under alkaline conditions ''in situ''. In the
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. It was developed by the chemist James Marsh and first published in 1836. The meth ...
, used for arsenic determination, hydrogen is generated by contacting
zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...
powder with
hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...
. 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 Arsine (IUPAC name: arsane) is an inorganic compound with the formula As H3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic. Despite its lethality, it finds some applications in th ...
gas (AsH3), while in hyperalkaline solution, the degassing of the reduced
ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
(NH3) is greatly facilitated.


Long-debated question of the nascent hydrogen

Since the mid-19th century the existence of true
nascent hydrogen Nascent hydrogen is an outdated concept in organic chemistry that was once invoked to explain dissolving-metal reactions, such as the Clemmensen reduction and the Bouveault–Blanc reduction. Since organic compounds do not react with H2, a specia ...
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 chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are common reducing agents include hydrogen, carbon ...
in the absence of a metal catalyst. Nascent hydrogen was supposed to be responsible for the reduction of arsenate or nitrate in
arsine Arsine (IUPAC name: arsane) is an inorganic compound with the formula As H3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic. Despite its lethality, it finds some applications in th ...
or
ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
respectively. Nowadays, isotopic evidence has closed the nascent hydrogen debate, presently considered to be a '' Gedanken'' artifact of romanticism.


See also

*
Kjeldahl method The Kjeldahl method or Kjeldahl digestion () in analytical chemistry is a method for the quantitative determination of a sample's organic compound, organic nitrogen plus ammonia/ammonium (NH3/NH4+). Without modification, other forms of inorganic ni ...
* Nitrate test * Nitrite test *
Nascent hydrogen Nascent hydrogen is an outdated concept in organic chemistry that was once invoked to explain dissolving-metal reactions, such as the Clemmensen reduction and the Bouveault–Blanc reduction. Since organic compounds do not react with H2, a specia ...
*
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. It was developed by the chemist James Marsh and first published in 1836. The meth ...
* Detection of: **
Arsine Arsine (IUPAC name: arsane) is an inorganic compound with the formula As H3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic. Despite its lethality, it finds some applications in th ...
**
Stibine Stibine (IUPAC name: stibane) is a chemical compound with the formula Sb H3. A pnictogen hydride, this colourless, highly toxic gas is the principal covalent hydride of antimony, and a heavy analogue of ammonia. The molecule is pyramidal with H� ...
*
Raney nickel Raney nickel , also called spongy nickel, is a fine-grained solid composed mostly of nickel derived from a nickel–aluminium alloy. Several grades are known, of which most are gray solids. Some are pyrophoric, but most are used as air-stable s ...
, prepared from an Al, Ni alloy also dissolved in concentrated
NaOH Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base and alkali t ...
* Zinc-copper couple


References


External links


Devarda's alloy - Substance Summary (SID 24856330)
( PubChem Substance)
Safety data for Devarda's alloy

Sigma Aldrich: Devarda’s alloy purum, for preparative purposes, grit





Further reading

* * {{aluminium alloys Aluminium alloys Copper alloys Name reactions Hydrogen Reducing agents Aluminium–copper alloys