Thursday, 2 February 2012

Ammonium (ortho)molybdate - (NH4)2MoO4 - min. 99 % - 100 g

Chemical formula: (NH4)2MoO4.4H2O

Synonyms: ammonium orthomolybdate tetrahydrate, ammonium molybdate tetrahydrate

Amount: 100 g

Appearance and odour: white crystalline powder without appreciable odour

Grade: min. 99 %

Packaging: professional wide necked, white HDPE bottle with blue conical seal cap and tamper ring. Labelled. Bottle and cap are UN approved and reusable.

Description and uses: an important, highly water soluble molybdenum compound.

It is perhaps most used for a simple qualitative test for phosphates: acidification of the sample and adding ammonium orthomolybdate results in a yellow colouration in the case of a phosphate positive sample.

Quantitative determination is also possible. From the relevant Wikipedia entry:

Colorimetric determination of P, As, Si and Ge

The determination of phosphorus, arsenic, silicon and germanium are examples of the use of heteropoly-molybdenum blue in analytical chemistry. The following example describes the determination of phosphorus. A sample containing the phosphate is mixed with an acid solution of MoVI, for example ammonium molybdate, to produce PMo12O403−, which has an α-Keggin structure. This anion is then reduced by, for example, ascorbic acid or SnCl2, to form the blue coloured β-keggin ion, PMo12O407−. The amount of the blue coloured ion produced is proportional to the amount of phosphate present and the absorption can be measured using a colorimeter to determine the amount of phosphorus. Examples of procedures are:

• the analysis of phosphate in sea water.
• standard methods for determining phosphorus and silicon content of metals and metal ores. (e.g. BSI and ISO standards)
• the determination of germanium and arsenic

The comparison of the measured absorption against readings taken for analyses of standard solutions means that a detailed understanding of the structure of the blue complex was unnecessary.
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CAS: 13746-66-2
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