Ammonium phosphomolybdate

Phosphorus. The presence of phosphorus may be indicated by a smell of phosphine during the sodium fusion. Treat 1 ml. of the fusion solution with 3 ml. of eoneentrated nitric acid and boil for one minute. Cool and add an equal volume of ammonium molybdate reagent. Warm the mixture to 40-50°, and allow to stand. If phosphorus is present, a yellow erystalline precipitate of ammonium phosphomolybdate wUl separate. 

Fig. 4.1 Adsorption isotherms of some organic vapours on ammonium phosphomolybdate outgassed at 180°C. The isotherm temperatures (reading downwards) were 25°C, 25°C, 25°C, 0°C.

Evidence of a different kind is furnished by the fact that the Gurvitsch rule (p. 113) is often obeyed by systems showing Type I isotherms " the amounts of different adsorptives taken up by a given adsorbent, when expressed as a volume of liquid, agree within a few per cent. The order of agreement is illustrated by the typical examples in Table 4.1 for the adsorption of n-alkanes on ammonium phosphomolybdate, and in Table 4.2 which refers to a variety of adsorptives on a silica gel. It must be admitted, however, that there are cases where considerable deviations from the Gurvitsch mle are found, even though the isotherms are of Type 1. Thus, in Table 4.3 the variation in values of the saturation uptake is far outside... 

Fig. 4J1 Adsorption isotherms on ammonium phosphomolybdate powder. (1), (2), before pre-adsorption of nonane (3), (4) after preadsorption of nonane. (1), (4), nitrogen (77 K) (2), (3), carbon tetrachloride (298 K). Adsorption is expressed in mm (liquid).

Phosphoms determination involves the conversion of phosphoms to soluble phosphate by digesting the coal ash with a mixture of sulfuric, nitric, and hydrofluoric acids (18). Phosphate is precipitated as ammonium phosphomolybdate, which may be reduced to give a blue solution that is determined colorimetricaHy or volumetricaHy (D2795) (18). 

This ammonium phosphomolybdate complex is yellow, but if mildly reduced by ascorbic acid in the presence of potassium antimonyl tartrate a solution of stable bluish-purple color ( molybdenum blue ) develops after about ten minutes, which has its strongest absorption at 882 pm (Fig. 4.6). Other mild reducing agents have also been used, including tin(II) chloride, or hydrazine sulfate, which give maximum absorbances at slightly different wavelengths. The intensity of the color which develops is linearly proportional to the... 

Reacts with phosphates or arsenates to form ammonium phosphomolybdate (NH4)3P04 I2M0O3, or ammonium arsenomolybdate, (NH4)3As04 I2M0O3. 

Although we must not underestimate the importance of coordination compounds such as ammonium phosphomolybdate (for the determination of phosphorus and more recently as an inor-... 

As Ammonium Phosphomolybdate. The phosphoric acid is separated from the nitric acid solution of the ash as ammonium phosphomolybdate. 

The ammonium phosphomolybdate thus obtained is collected in a tared Gooch crucible charged with asbestos and washed with water acidified with 1% of nitric acid (D 1-18) until a drop of the filtrate leaves no residue when evaporated on a watch-glass the crucible is heated in an oven at 70-80° to constant weight ammonium phosphomolybdate x 0-0378 — phosphoric anhydride. 

Thalictine (60), C37H40N2O6, an amorphous, air-sensitive base, was isolated from Thalictrum thunbergii D.C. as its nitrate salt, mp 226-228°C. The alkaloid shows [a]D -15.8° (CHC13), -12.2° (MeOH), IR 3550 cm"1 (OH), and it gave a positive ammonium phosphomolybdate color test for a cryptophenol. The... 

Ammonium molybdate Addition of 2 to 3 ml of excess reagent to approximately 0.5-ml sample gives yellow precipitate of ammonium phosphomolybdate, which is soluble in ammonia solution and in solutions of caustic alkalis large quantities of hydrochloric acid interfere... 

Phosphorus combined in organic compounds, or as phosphide in metals, is also estimated after oxidation by precipitation as ammonium phosphomolybdate or magnesium ammonium phosphate, with the subsequent treatment which is described on pp. 181—183. The methods by which the phosphorus is brought into solution vary with the nature of the material which is being analysed. Organic compounds are oxidised in a sealed tube with fuming nitric acid or in a flask by a mixture of concentrated sulphuric and nitric acids. 

The precipitates obtained with magnesia mixture (magnesium chloride in ammoniacal solution), or ferric chloride in an acid solution to which sodium acetate has been added, are often used as tests for phosphate (see p. 180), and in the latter case the phosphate is removed from solution as ferric phosphate. Another common test is the formation of yellow ammonium phosphomolybdate when, a nitric acid solution of ammonium molybdate is added to phosphate solution (see pp. 180, 181). 

An ammonium phosphomolybdate precipitate is treated as described under (2c) (p. 182) for conversion into MgNH4P04. The washed precipitate of MgNH4P04 may be determined volumetrically by solution in a known quantity in excess of standard hydrochloric acid and baek-titration with decinormal alkali using methyl orange, thus... 

B. Add 10 mL of ammonium molybdate TS to 10 mL of a warm 1 100 aqueous solution in a slight excess of nitric acid. A yellow precipitate of ammonium phosphomolybdate forms. 

A green-yellow precipitate of ammonium phosphomolybdate forms that is soluble in 6 N ammonium hydroxide. 

A. Dissolve about 200 mg of sample in 10 mL of 1.7 A nitric acid, and add, dropwise, ammonium molybdate TS. A green-yellow precipitate of ammonium phosphomolybdate forms that is soluble in 6 N ammonium hydroxide. 

TOie Hb activity- Is carried down by a Fe(aH)3 ppt. from alkaline (HEilaMoCli soln. and then the Ho is ppted. as ammonium phosphomolybdate from acidic spin. 

Heteropolyacids similarly form a group of compounds in which it has only just been possible to give the correct stoichiometric composition, after the structural principles had become better known by X-ray analysis. The best-known heteropolyacid is actually phosphomolybdic acid, in fact the test for phosphate ions with ammonium molybdate leads to the formation of the well-known, slightly soluble ammonium phosphomolybdate discovered by Berzelius, gross composition after drying, (NH4)3P04.i2Mo03. 

Arsenates give a similar reaction on boiling (see under Arsenic, Section 111,13, reaction 4). Both ammonium phosphomolybdate and ammonium... 

Sodium phosphate solution yellow, crystalline precipitate of ammonium phosphomolybdate in the presence of excess nitric acid (cf. phosphates, Section IV.28, reaction 4). 

Ammonium molybdate solution No precipitate is produced in the presence of ammonium nitrate and nitric acid, a soluble molybdovanadate being formed (compare phosphate). If the vanadate is mixed with a phosphate, much of the vanadium is coprecipitated with the ammonium phosphomolybdate. 

Ammonium Dimolybdate, (NH4)2Mo.j07.H20, exists as mono-clinic (prismatic) crystals. A compound (NH4).2Mo20,.3NH2 has been prepared by addition of ammonium hydroxide of medium strength to solid ammonium phosphomolybdate. This substance loses ammonia, yielding the dimolybdate. 

If higher sensitivities are desired then the ammonium phosphomolybdate product may be reduced with stannous chloride or ascorbic acid in order to give soluble molybdenum blue [24]. Spectrophotometric determination of the blue absorbance at 885 nm gives a detection limit of 0.003 mg/L phosphate, stated as phosphorus (3 ppb in freshwater) or 0.0092 mg/L as expressed phosphate [24]. 

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