Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Ammonium Molybdate Tetrahydrate (Ammonium Heptamolybdate Tetrahydrate)
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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 Ammonium Molybdate Tetrahydrate 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 Matter, Chloride, Nitrate, Arsenate, Phosphate, Silicate, Phosphate, Sulfate, Heavy Metals, Magnesium, Potassium, and Sodium.
(NH4)6Mo7O24 · 4H2O
Formula Wt 1236.00
CAS No. 12054-85-2
GENERAL DESCRIPTION Typical appearance . . . . . . . . Applications . . . . . . . . . . . . . Change in state (approximate) . Aqueous solubility . . . . . . . . .
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colorless or white solid; sometimes with a slight green or yellow tint determination of phosphates, arsenates, and lead loses one water at 90 °C; decomposes at 190 °C soluble
SPECIFICATIONS Assay (as MoO3) . . . . . . . . . . . . . . . . . . . . . 81.0–83.0%
Insoluble matter . . . . . . . . . . . . . . . . . . Chloride (Cl) . . . . . . . . . . . . . . . . . . . . Nitrate (NO3) . . . . . . . . . . . . . . . . . . . . Arsenate, phosphate, and silicate (as SiO2) . Phosphate (PO4) . . . . . . . . . . . . . . . . . . Sulfate (SO4) . . . . . . . . . . . . . . . . . . . . Heavy metals (by ICP–OES) . . . . . . . . . . .
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© 2017 American Chemical Society
Maximum Allowable 0.005% 0.002% Passes test 0.001% 5 ppm 0.02% 0.001%
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ACS Reagent Chemicals ACS Reagent Chemicals; American Chemical Society: Washington, DC, 2017.
DOI:10.1021/acsreagents.4028 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Magnesium (Mg) . . . . . . . . . . . . . . . . . . . . . 0.005% Potassium (K) . . . . . . . . . . . . . . . . . . . . . . . 0.01% Sodium (Na) . . . . . . . . . . . . . . . . . . . . . . . . 0.01%
TESTS Assay
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(By precipitation titration of molybdate). Weigh accurately about 0.7 g, and dissolve in 100 mL of water. Adjust the pH of the solution to 4.0 with 1% nitric acid reagent solution. Add hexamethylenetetramine reagent solution to a pH of 5–6, using a pH meter. Heat the solution to 60 °C, and titrate with 0.1 M lead nitrate volumetric solution. Add 0.2 mL of 1.1% PAR indicator solution, and titrate from yellow color to the first permanent pink end point. One milliliter of 0.1 M lead nitrate corresponds to 0.01439 g of MoO3.
Insoluble Matter [Part 2: Gravimetric Methods; Insoluble Matter]. Use 20 g dissolved in 200 mL of water.
Chloride [Part 2: Colorimetry and Turbidimetry; Chloride]. Use 0.5 g.
Nitrate Dissolve 1.0 g in 10 mL of water containing 5 mg of sodium chloride. Add 0.10 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 70 mL of water. For the control, dissolve 0.5 g in 70 mL of water and add 0.02 mg of silica (SiO2). These solutions are prepared in containers other than glass to avoid excessive silica contamination. Adjust the pH to between 3 and 4 (pH paper) with dilute hydrochloric acid (1:9), then transfer to glass containers and treat each solution as follows: add 1–2 mL of bromine water and adjust the pH to between 1.7 and 1.9 (using a pH meter) with dilute hydrochloric acid (1:9). Heat just to boiling, but do not boil, and cool to room temperature. Dilute with water to 90 mL, add 10 mL of hydrochloric acid, and transfer to a separatory funnel. Add 1 mL of butyl alcohol and 30 mL of 4-methyl-2-pentanone, shake vigorously, and allow the phases to separate. Draw off and discard the aqueous phase and wash the ketone phase three times with 10 mL portions of dilute hydrochloric acid (1:99), discarding each aqueous phase. To the washed ketone phase, add 10 mL of dilute hydrochloric acid (1:99) to which has just been added 1.2 mL of a freshly prepared 2% solution of stannous chloride in hydrochloric acid. 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)].
© 2017 American Chemical Society
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ACS Reagent Chemicals ACS Reagent Chemicals; American Chemical Society: Washington, DC, 2017.
DOI:10.1021/acsreagents.4028 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Sulfate [Part 2: Colorimetry and Turbidimetry; Sulfate; Procedure for Sulfate, Method 2]. Use 5 mL of nitric acid.
Heavy Metals ([Part 2: Trace and Ultratrace Elemental Analysis; Inductively Coupled Plasma−Optical Emission Spectroscopy (ICP–OES); Calculation of Heavy Metals (by ICP–OES) Results], by ICP–OES). Use 1.0 g sample..
Magnesium, Potassium, and Sodium
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(By flame AAS, [Part 2: Trace and Ultratrace Elemental Analysis; Atomic Absorption Spectroscopy; Analysis; Procedure for Flame AAS]).
For the Determination of Magnesium, Potassium, and Sodium
S a m p l e S t o c k S o l u t i o n . Dissolve 5.0 g of sample in 60 mL of water, and add 20 mL of 10% sulfuric acid. Transfer to a 100 mL volumetric flask, and dilute to the mark with water (1 mL = 0.05 g).
For the Determination of Magnesium, Potassium, and Sodium
Element
Wavelength (nm)
Sample Wt (g)
Standard Added (mg)
Flame Type*
Background Correction
Mg
285.2
0.20
0.01; 0.02
A/A
Yes
K**
766.5
0.20
0.01; 0.02
A/A
No
Na
589.0
0.20
0.01; 0.02
A/A
No
*A/A is air/acetylene.**The means of absorbing radiation below 650 nm, such as a red filter and the use of an alkali salt to suppress ionization, is critical for this analysis.
© 2017 American Chemical Society
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ACS Reagent Chemicals ACS Reagent Chemicals; American Chemical Society: Washington, DC, 2017.
DOI:10.1021/acsreagents.4028 ACS Reagent Chemicals, Part 4
