Jones reductor
Encyclopedia
A Jones reductor is a device which can be used to reduce
a metal ion in aqueous solution to a very low oxidation state
. The active component is a zinc
/mercury
amalgam
. It can be used to prepare solutions of ions, such as chromium
(II), Cr2+, and uranium
(III), U3+, which are immediately oxidized on contact with air.
and are reduced to elemental mercury, forming the amalgam, which is a kind of alloy
of both metals, on the metal surface. The amalgam is thoroughly washed by decantation
and placed in a long glass tube, similar to a chromatography column
, equipped with a stopcock and a means to support the amalgam, such as a sintered-glass disk. The outlet of the tube is connected to a collection flask by an air-tight seal and the collection flask is connected with a vacuum source.
To use the reductor, the solution to be reduced is placed at the top of the tube, and then is drawn through it. If the column is loosely packed, the solution may pass though without assistance, but if the tube is tightly packed, the pressure in the collecting flask may need to be reduced. In effect this configuration is similar to that used for column chromatography as the extent of reduction increases to 100% as the solution passes down the tube and the product is completely separated from the starting material.
of −0.76 V. The amalgam does not have a passive layer so it is a more effective reducing agent than zinc metal. The Jones reductor is useful for preparing solutions of titanium
(III), vanadium
(II), chromium
(II), molybdenum
(III), niobium
(III) and uranium
(III). All these ions are extremely susceptible to oxidation. For example, the reductor can be used in the preparation of crystalline chromous acetate. This solid is moderately stable in air and is a good starting material for the preparation of other chromium(II) compounds.
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
a metal ion in aqueous solution to a very low oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
. The active component is a 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...
/mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
amalgam
Amalgam (chemistry)
An amalgam is a substance formed by the reaction of mercury with another metal. Almost all metals can form amalgams with mercury, notable exceptions being iron and platinum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore.The...
. It can be used to prepare solutions of ions, such as chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
(II), Cr2+, and uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
(III), U3+, which are immediately oxidized on contact with air.
Preparation and use
Amalgamated zinc is first prepared by treating zinc metal with a 2% solution of mercury(II) chloride, in a beaker. The metal may be in the granulated form or as shavings, wool, or 20-30 mesh powder. The mercury ions are able to penetrate the passive layerPassivation
Passivation is the process of making a material "passive", and thus less reactive with surrounding air, water, or other gases or liquids. The goal is to inhibit corrosion, whether for structural or cosmetic reasons. Passivation of metals is usually achieved by the deposition of a layer of oxide...
and are reduced to elemental mercury, forming the amalgam, which is a kind of alloy
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 both metals, on the metal surface. The amalgam is thoroughly washed by decantation
Decantation
Decantation is a process for the separation of mixtures. This is achieved by carefully pouring a solution from a container in order to leave the precipitate in the bottom of the original container...
and placed in a long glass tube, similar to a chromatography column
Column chromatography
Column chromatography in chemistry is a method used to purify individual chemical compounds from mixtures of compounds. It is often used for preparative applications on scales from micrograms up to kilograms.The main advantage of column chromatography is the relatively low cost and disposability...
, equipped with a stopcock and a means to support the amalgam, such as a sintered-glass disk. The outlet of the tube is connected to a collection flask by an air-tight seal and the collection flask is connected with a vacuum source.
To use the reductor, the solution to be reduced is placed at the top of the tube, and then is drawn through it. If the column is loosely packed, the solution may pass though without assistance, but if the tube is tightly packed, the pressure in the collecting flask may need to be reduced. In effect this configuration is similar to that used for column chromatography as the extent of reduction increases to 100% as the solution passes down the tube and the product is completely separated from the starting material.
Applications
Amalgamated zinc is a powerful reducing agent, with a standard redox potentialStandard electrode potential (data page)
The values of standard electrode potentials are given in the table below in volts relative to the standard hydrogen electrode and are assembled from referencesThe values are for the following conditions:* the temperature of 298.15 K ;...
of −0.76 V. The amalgam does not have a passive layer so it is a more effective reducing agent than zinc metal. The Jones reductor is useful for preparing solutions of titanium
Titanium(III) chloride
Titanium chloride is the inorganic compound with the formula TiCl3. At least four distinct species have this formula; additionally hydrated derivatives are known...
(III), vanadium
Vanadium
Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature...
(II), chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
(II), molybdenum
Molybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...
(III), niobium
Niobium
Niobium or columbium , is a chemical element with the symbol Nb and atomic number 41. It's a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite...
(III) and uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
(III). All these ions are extremely susceptible to oxidation. For example, the reductor can be used in the preparation of crystalline chromous acetate. This solid is moderately stable in air and is a good starting material for the preparation of other chromium(II) compounds.