Ammonium molybdate solution

Discussion. When a solution of an orthophosphate is treated with a large excess of ammonium molybdate solution in the presence of nitric acid at a temperature of 20-45 °C, a precipitate is obtained, which after washing is converted into ammonium molybdophosphate with the composition (NH4)3[P04,12Mo03]. This may be titrated with standard sodium hydroxide solution using phenolph-thalein as indicator, but the end point is rather poor due to the liberation of ammonia. If, however, the ammonium molybdate is replaced by a reagent containing sodium molybdate and quinoline, then quinoline molybdophosphate is precipitated which can be isolated and titrated with standard sodium hydroxide ... 

The reaction velocity is comparatively slow, but increases with increasing concentration of acid. The addition of three drops of a neutral 20 per cent ammonium molybdate solution renders the reaction almost instantaneous, but as it also accelerates the atmospheric oxidation of the hydriodic acid, the titration is best conducted in an inert atmosphere (nitrogen or carbon dioxide). 

Better results are obtained by transferring 25.0 mL of the diluted hydrogen peroxide solution to a conical flask, and adding 100 mL 1M(1 20) sulphuric acid. Pass a slow stream of carbon dioxide or nitrogen through the flask, add 10 mL of 10 per cent potassium iodide solution, followed by three drops of 3 per cent ammonium molybdate solution. Titrate the liberated iodine immediately with standard 0.1M sodium thiosulphate in the usual way. 

Prepare the 10 per cent ammonium molybdate solution by dissolving 25 g ammonium molybdate in water and diluting to 250 mL in a polythene bottle. It keeps for about 4 weeks. 

Molybdenum blue method. When arsenic, as arsenate, is treated with ammonium molybdate solution and the resulting heteropolymolybdoarsenate (arseno-molybdate) is reduced with hydrazinium sulphate or with tin(II) chloride, a blue soluble complex molybdenum blue is formed. The constitution is uncertain, but it is evident that the molybdenum is present in a lower oxidation state. The stable blue colour has a maximum absorption at about 840 nm and shows no appreciable change in 24 hours. Various techniques for carrying out the determination are available, but only one can be given here. Phosphate reacts in the same manner as arsenate (and with about the same sensitivity) and must be absent. 

Ammonium molybdate solution. Dissolve 50 g ammonium molybdate, (NH4)6 Mo7024,4H20, in warm water and dilute to 1 L in a graduated flask. Filter the solution before use. 

Reagents. Ammonium molybdate solution. Dissolve 8.0 g ammonium molybdate crystals in water, add 9 mL concentrated sulphuric acid, and dilute to 100 mL. 

Procedure. The sample solution, free from interfering elements and radicals, may conveniently occupy a volume of about 50 mL and contain between 0.01 and 0.1 mg of silica the pH should be 4.5-5.0 Add 1 mL of the ammonium molybdate solution and, after 5 minutes, add 5 mL of the tartaric acid solution and mix. Introduce 1.0 mL of the reducing agent and dilute to 100 mL in a graduated flask. Measure the absorbance at ca 815 nm after 20 minutes against de-ionised water. 

Analytical thin-layer chromatography was performed on E. Merck silica gel 60 F254 plates (0.25 mm) and compounds were visualized by dipping the plates in a cerium sulfate-ammonium molybdate solution followed by heating. 

Ammonium molybdate solution. Dissolve 6 g of ammonium molybdate in distilled water in a 250-mL Erlenmeyer flask, dilute to 100 mL with distilled water, and swirl to make homogeneous. Prepare just prior to the run. 

A small portion of the hydrolysis solution was strongly acidified with concentrated nitric acid, and warm ammonium molybdate solution added. No visible change took place, and it was only after some minutes boiling that a yellow coloration was produced. This is good evidence against equation (c). Presumably sodium di-isopropyl phosphate requires to be broken down with boiling nitric acid before phosphoric acid is produced. 

Ammonium molybdate solution - add 15 g of ammonium molybdate ((NH4)gMo7024.4H20) to about 900 ml warm water and stir to dissolve. Make up to 1 I in a volumetric flask and filter before use. 

Vanadate-molybdate reagent - mix the ammonium molybdate solution with the ammonium vanadate solution in the ratio 2 3 molybdate vana-date. For optimum reproducibility, make up fresh each day just before use. 

Procedure (determination of inorganic phosphate (a) in the acetic acid extract). The 8-hydroxyquinoline forms a precipitate in acidic ammonium molybdate solution, which will interfere unless the aliquot is <5 ml. It should therefore be removed by ignition as follows. Transfer 10 ml acetic acid extract to a 45-ml silica basin, add 0.5 ml 1 M magnesium acetate and evaporate to dryness on a water-bath. (Note do not use magnesium nitrate, which reacts adversely on heating with 8-hydroxyquinoline.)... 

Chemical deposition of both M0S2 and MoSei has been reported from ammonium molybdate solution [76,77], For the sulphur and selenium sources, thioacetamide and selenosulphate were used, respectively. Ammonium hydroxide was added to the sulphide solution, while an acetic acid/ammonium acetate buffer was used with the selenide solution (pH values were not given). Reducing agents (either hydrazine [76] or sodium dithionite [77]) were added to the baths. Deposition was started at 90-100°C, followed by lowering to room temperature. 

Pour 2-3 ml of a 10 % nitric acid solution into 2-3 ml of a 20 % ammonium molybdate solution. What substance precipitates What is its colour Wash the precipitate with water by decantation and divide it into two parts. React one part of the precipitate with an excess of concentrated hydrochloric acid and the other with a 20% sodium hydroxide solution. Explain the results. Write the equations of the reactions. Under what conditions does molybde-num(Vl) oxide dihydrate form ... 

Thiosalts and Sulphides of Molybdenum and Tungsten. Pour 2-3 ml of an ammonium molybdate solution into one test tube and 2-3 ml of a sodium tungstate solution into another one. Add 2-3 drops of a 25 % ammonia solution to each solution and pass a stream of hydrogen sulphide through them from a Kipp gas generator. What compounds form Acidify the solutions with a 10% hydrochloric... 

Reduction of MoIybdenum(VI) and Tungsten VI) Compounds. Pour 3 ml of an ammonium molybdate solution into each of four test tubes, acidify with a 2 N hydrochloric acid solution, and heat up to boiling. Add solutions of sulphuric acid, hydrogen sulphide, and tin(Il) chloride to three of the tubes, respectively, and throw one or two small pieces of zinc into the last tube. Perform similar experiments using sodium tungstate as the initial reactant. Write the equations of the reactions. 

In order to prevent spirting over of phosphoric acid, the flask should be provided with a Kjeldahl connecting bulb tube. The distillate must be tested with ammonium molybdate solution for phosphoric acid.. 

The ammonium molybdate solution should be added to the nitric acid gradually and with constant rotation never otherwise. 

Phosphates. — Slake 3 gm. of calcium oxide with 10 cc. of water, dissolve in 25 cc. of nitric acid, and add 25 cc. of ammonium molybdate solution. No yellow precipitate should form on standing twelve hours at 30 to 403 C. 

Alternatively, the compound can be obtained by letting the deep-red solution, obtained after mixing the solutions, stand at room temperature for 2-4 hours. In this case the product is usually contaminated with crystals of ammonium tetrathio-molybdate(VI), (NH4)2MoS4. The compound also can be obtained in poor yields by dissolving freshly precipitated copper(II) sulfide in ammoniacal ammonium molybdate solution saturated with hydrogen sulfide. Undissolved copper(II) sulfide is removed by filtration after 3-5 minutes, and the copper(I) ammonium thiomolybdate(VI) is obtained by boiling as above. 

Richtmyer and Hudson48 have found that the rotation of several polyols is augmented in an acidified ammonium molybdate solution, and to a much greater extent than in borate solutions. 

Phosphates Ammonium molybdate solution made from 3 g of ammonium molybdate in 20 m/ of perchloric acid (40%) and 5 ml of concentrated hydrochloric acid in 200 m/ of water ( 10 min 100°C) subsequently saturated hydrazine sulphate solution (20 min 110°C)... 

Catalyst Preparation. The catalysts were prepared by impregnation of -alumina extrudates ( SA=253 m /g ). Each impregnation was followed by drying overnight at 120°C and calcination at the indicated temperatures during one hour. Molybdenum was brought on the support as an ammonium molybdate solution cobalt and nickel as nitrate solutions. Each component was impregnated separately. 

Special test Blue ring test — when solution of thiosulfate mixed with ammonium molybdate solution is poured slowly down the side of a test tube that contains concentrated sulfuric acid, a blue ring is formed temporarily at the contact zone... 

If the water is first concentrated to one-fiftieth of its bulk, tests may be carried out for magnesia and phosphates. The former is precipitated as magnesium ammonium phosphate on standing for some twenty-four hours after addition of sodium phosphate solution to the water rendered alkaline with ammonium hydroxide in the presence of chloride. It is assumed that any lime has previously been removed with ammonium oxalate. Phosphates are precipitated as yellow phosphomolybdate on adding excess of ammonium molybdate solution to the water acidified with nitric acid, and warming. 

Phosphate Evaporate 400 mg of sample to dryness on a steam bath. Dissolve the residue in 25 mL of approximately 0.5 N sulfuric acid, add 1 mL of ammonium molybdate solution [500 mg of (NH4)5Mo7024 4H20 in each 10 mL of water] and 1 mL of p-methylaminophenol sulfate TS, and allow it to stand for 2 h. Any blue color does not exceed that produced by 2.0 mL of Phosphate Standard Solution (20 pig PO4) (see Solutions and Indictors) in an equal volume of solution containing the quantities of the reagents used in the test. Residue on Evaporation Evaporate 25 g of sample to dryness in a tared porcelain or silica dish on a steam bath, and... 

Acid Molybdate Solution Dilute 25 mL of ammonium molybdate solution [7 g of (NH MovC A O in sufficient water to make 100 mL] to 200 mL with water, and slowly add 25 mL of 7.5 N sulfuric acid. 

Ammonium Molybdate Solution (5%) Dissolve 50 g of ammonium molybdate tetrahydrate, (NLLOeMoyO rdL O, in 900 mL of warm water, cool to room temperature, dilute to 1000 mL with water, and mix. 

Ammonium Molybdate Solution Dissolve 2.5 g of ammonium molybdate [(ISnLOsMoC -d O] (Merck, Catalog No. 1182) in water, and dilute to 100 mL. 

Reagent C Mix 3 volumes of 1 M Sulfuric Acid with 1 volume of Ammonium Molybdate Solution, then add 1 volume of Ascorbic Acid Solution, and mix well. Prepare fresh daily. 

Units of catalase, into a 200-mL beaker. Rapidly add 100 mL of Peroxide Substrate Solution, previously adjusted to 25°, and stir immediately for 5 to 10 s. Cover the beaker, and incubate at 25° 1° until the reaction is completed. Stir vigorously for 5 s, and then pipet 4.0 mL from the beaker into a 50-mL Erlenmeyer flask. Add 5 mL of 2 N sulfuric acid to the flask, mix, then add 5.0 mL of 40% potassium iodide solution, freshly prepared, and 1 drop of Ammonium Molybdate Solution (1%), and mix. While continuing to mix, titrate rapidly to a colorless endpoint with 0.250 N Sodium Thiosulfate, recording the volume, in milliliters, required as S. Perform a blank determination with 4.0 mL of Peroxide Substrate Solution, and record the volume required, in milliliters, as B. 

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