Ammonium heptamolybdate is the

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

whose

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

is (NH₄)₆Mo₇O₂₄, normally encountered as the tetrahydrate. A dihydrate is also known. It is a colorless solid, often referred to as ammonium paramolybdate or simply as ammonium molybdate, although "ammonium molybdate" can also refer to

ammonium orthomolybdate Ammonium orthomolybdate is the inorganic compound with the chemical formula (NH4)2MoO4. It is a white solid that is prepared by treating molybdenum trioxide with aqueous ammonia. Upon heating these solutions, ammonia is lost, to give ammonium h ...

, (NH₄)₂MoO₄, and several other compounds. It is one of the more common molybdenum compounds.

Synthesis

Ammonium heptamolybdate is easily prepared by dissolving molybdenum trioxide in an excess of aqueous ammonia and evaporating the solution at room temperature. While the solution evaporates, the excess of ammonia escapes. This method results in the formation of six-sided transparent prisms of the tetrahydrate of ammonium heptamolybdate. Solutions of ammonium paramolybdate react with acids to form molybdic acid and an

ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...

salt. The pH value of a concentrated solution will lie between 5 and 6.

Structure

The compound was first analyzed crystallographically by Lindqvist, but has been reanalyzed.Evans, H.T., Jr.; Gatehouse, B. M.; Leverett, P. "Crystal Structure of the Heptamolybdate(VI) (paramolybdate) ion, (Mo₇O₂₄)⁶⁻, in the ammonium and potassium tetrahydrate salts" Journal of the Chemical Society. Dalton Transactions, Inorganic Chemistry1975, p.505-p514. All Mo centers are octahedral. Some oxide ligands are terminal, some doubly bridging, and a few are triply

bridging ligand In coordination chemistry, a bridging ligand is a ligand that connects two or more atoms, usually metal ions. The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually r ...

s. 224px, left, The salt contains the heptamolybdate hexaanion.

Uses

*as an analytical

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

to measure the amount of

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phospho ...

silicates In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...

arsenate The arsenate ion is . An arsenate (compound) is any compound that contains this ion. Arsenates are salts or esters of arsenic acid. The arsenic atom in arsenate has a valency of 5 and is also known as pentavalent arsenic or As(V). Arsenate res ...

s and

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

aqueous solution 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, or sodium chloride (NaCl), in water would be re ...

(e.g. pigments, river water, sea water etc.) *in the production of

molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...

metal and

ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...

s *in the preparation of dehydrogenation and

desulfurization Desulfurization or desulphurisation is a chemical process for the removal of sulfur from a material. This involves either the removal of sulfur from a molecule (''e.g.'' A=S → A:) or the removal of sulfur compounds from a mixture such as oil refin ...

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

s *in the fixing of metals *in

electroplating Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the reduction of cations of that metal by means of a direct electric current. The part to be ...

*in fertilizers for crops. *as a negative stain in biological electron microscopy, typically in the 3–5% (vol/vol) concentration range and in the presence of trehalose; or at saturated concentration to perform cryo-negative staining. *For the detection of recreational drugs as a component of the

Froehde reagent The Froehde reagent is used as a simple spot-test to presumptively identify alkaloids, especially opioids, as well as other compounds. It is composed of a mixture of molybdic acid or a molybdate salt dissolved in hot, concentrated sulfuric acid, wh ...

Related compounds

Potassium heptamolybdate, also obtained as the tetrahydrate, is very similar to the ammonium salt.

Safety

Molybdates are typically of low toxicity, so much so that few reports of incidents have ever been reported.

Synthesis

Structure

Uses

Related compounds

Safety

References

See also