Molybdenum Trioxide - ACS Reagent Chemicals (ACS Publications)

Monograph pubs.acs.org/doi/book/10.1021/acsreagents

Molybdenum Trioxide (Molybdenum(VI) Oxide; Molybdic Acid Anhydride)

Downloaded by CORNELL UNIV on June 17, 2017 | http://pubs.acs.org Publication Date (Web): February 28, 2017 | doi: 10.1021/acsreagents.4231

Part 4, Monographs for Reagent Chemicals: General Descriptions, Specifications, and Tests eISBN: 9780841230460 Tom Tyner Chair, ACS Committee on Analytical Reagents James Francis Secretary, ACS Committee on Analytical Reagents

ABSTRACT This monograph for Molybdenum Trioxide provides, in addition to common physical constants, a general description including typical appearance, applications, change in state (approximate), and aqueous solubility. The monograph also details the following specifications and corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay, Insoluble in Dilute Ammonium Hydroxide, Chloride, Nitrate, Arsenate, Phosphate, Silicate, Phosphate, Sulfate, Ammonium, and Heavy Metals.

MoO3

Formula Wt 143.96

CAS No. 1313-27-5

GENERAL DESCRIPTION Typical appearance . . . . . . . . Applications . . . . . . . . . . . . . Change in state (approximate) . Aqueous solubility . . . . . . . . .

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white, slightly yellow, green, or gray solid trace metal analysis melting point, 795 °C very slightly soluble

SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . ≥99.5% MoO3 Maximum Allowable Insoluble in dilute ammonium hydroxide. . . . . . 0.01% Chloride (Cl) . . . . . . . . . . . . . . . . . . . . . . . 0.002% Nitrate (NO3) . . . . . . . . . . . . . . . . . . . . . . . Passes test Arsenate, phosphate, and silicate (as SiO2) . . . . 0.001% Phosphate (PO4) . . . . . . . . . . . . . . . . . . . . . 5 ppm Sulfate (SO4) . . . . . . . . . . . . . . . . . . . . . . . 0.02% Ammonium (NH4) . . . . . . . . . . . . . . . . . . . . 0.002% Heavy metals (as Pb) . . . . . . . . . . . . . . . . . . 0.005%

© 2017 American Chemical Society

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ACS Reagent Chemicals ACS Reagent Chemicals; American Chemical Society: Washington, DC, 2017.

DOI:10.1021/acsreagents.4231 ACS Reagent Chemicals, Part 4

ACS Reagent Chemicals

Monograph

pubs.acs.org/doi/book/10.1021/acsreagents

TESTS Assay (By precipitation titration of molybdate). Weigh accurately about 0.6 g, and dissolve in 100 mL of 2.5% ammonium hydroxide reagent solution. Adjust the pH of the solution to 4.0 (using a pH meter) with 10% nitric acid reagent solution. Add hexamethylenetetramine reagent solution to a pH of 5–6. Heat the solution to 60 °C, and titrate with 0.1 M lead nitrate volumetric solution. Using 0.1% PAR indicator solution, titrate from yellow color to the first permanent pink end point. One milliliter of 0.1 N lead nitrate corresponds to 0.01439 g of MoO3.


Insoluble in Dilute Ammonium Hydroxide Dissolve 10 g in 120 mL of dilute ammonium hydroxide (1:6), heat to boiling, and digest in a covered beaker on a hot plate (~100 °C) for 2 h. Filter through a tared, preconditioned filtering crucible, wash thoroughly, and dry at 105 °C.

Chloride Dissolve 1.0 g in 4 mL of ammonium hydroxide, heat on a hot plate (~100 °C) until completely dissolved, and evaporate to dryness. Dissolve the residue in 20 mL of water, filter if necessary through a chloride-free filter, add 4 mL of nitric acid, and dilute with water to 30 mL. To 15 mL, add 1 mL of silver nitrate reagent solution. Any turbidity should not exceed that produced by 0.01 mg of chloride ion (Cl) in an equal volume of solution containing the quantities of reagents used in the test. The comparison is best made by the general method for chloride in colored solutions [Part 2: Colorimetry and Turbidimetry; Chloride].

Nitrate Grind 1.0 g with 9 mL of water and 1 mL of sodium chloride solution containing 5 mg of sodium chloride. Add 0.20 mL of indigo carmine reagent solution and 10 mL of sulfuric acid. The blue color should not be completely discharged in 5 min. (Limit about 0.003%.)

Arsenate, Phosphate, and Silicate Dissolve 2.5 g in 60 mL of water and enough silica-free ammonium hydroxide to effect dissolution (about 4 mL) in a platinum dish. For the control, dissolve 0.5 g in 60 mL of water and enough silica-free ammonium hydroxide to effect dissolution and add 0.02 mg of silica (SiO2). Heat on a hot plate (~100 °C) until the solutions are neutral as determined with an external indicator (at least 30 min). Cool, and adjust the pH to between 3 and 4 with an external indicator. Transfer to beakers, and dilute with water to 80 mL. Add enough bromine water to impart a distinct yellow color to the solutions. Adjust the pH of each solution to 1.8 with dilute hydrochloric acid (1:9) (using a pH meter). Heat just to boiling, and allow to cool to room temperature. (If a precipitate forms, it will dissolve when the solution is acidified in the next operation.) Add 10 mL of hydrochloric acid, and dilute with water to 100 mL. Transfer the solutions to separatory funnels, and add 30 mL of 4-methyl2-pentanone and 1 mL of butyl alcohol. Shake vigorously, and allow to separate. Draw off and discard the aqueous phase. Wash the ketone phase three times with 10 mL portions of dilute hydrochloric acid (1:99), discarding the aqueous phase each time. To the washed ketone phase, add 10 mL of dilute hydrochloric acid (1:99), to which has just been added 0.2 mL of a freshly prepared 2% stannous chloride reagent solution. Any blue color in the solution of the sample should not exceed that in the control.

Phosphate [Part 2: Colorimetry and Turbidimetry; Phosphate; Procedure for Phosphate, Method 3 (Precipitation)].


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ACS Reagent Chemicals

Monograph

pubs.acs.org/doi/book/10.1021/acsreagents

Sulfate Boil 1.0 g with 15 mL of dilute nitric acid (1:2) for 5 min. Cool thoroughly, dilute with water to 50 mL, mix well, and filter. Evaporate 10 mL of the filtrate to dryness on a hot plate (~100 °C). Dissolve the residue in 4 mL of water plus 1 mL of dilute hydrochloric acid (1:19), filter if necessary through a small filter, wash with two 2 mL portions of water, and dilute with water to 10 mL. Add 1 mL of 12% barium chloride reagent solution. Any turbidity should not exceed that produced by 0.04 mg of sulfate ion (SO4) in an equal volume of solution containing the quantities of reagents used in the test. Compare 10 min after adding the barium chloride to the sample and standard solutions.

Ammonium


Dissolve 1.0 g in 15 mL of freshly boiled 10% sodium hydroxide reagent solution, and dilute with water to 100 mL. To 50 mL, add 2 mL of Nessler reagent. Any color should not exceed that produced by 0.01 mg of ammonium ion (NH4) in an equal volume of solution containing 1.5 mL of 10% sodium hydroxide reagent solution and 2 mL of Nessler reagent. Use Nessler tubes for best results.

Heavy Metals Dissolve 1.0 g in 15 mL of 10% sodium hydroxide reagent solution, add 2 mL of ammonium hydroxide, and dilute with water to 40 mL. For the control, add 0.025 mg of lead ion (Pb) to 10 mL of the solution, and dilute with water to 40 mL. For the sample, dilute the remaining solution with water to 40 mL. Add 5 mL of freshly prepared hydrogen sulfide water to each, and mix. Any color in the solution of the sample should not exceed that in the control.


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Molybdenum Trioxide - ACS Reagent Chemicals (ACS Publications)

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