Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Sodium Arsenate Heptahydrate (Disodium Hydrogen Arsenate Heptahydrate) 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 Sodium Arsenate Heptahydrate 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, Arsenite, Chloride, Nitrate, Sulfate, Heavy Metals, and Iron.
Na2HAsO4 • 7H2O
Formula Wt 312.01
CAS No. 10048-95-0
GENERAL DESCRIPTION Typical appearance . . . . . . . . Applications . . . . . . . . . . . . . Change in state (approximate) . Aqueous solubility . . . . . . . . .
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white solid source of soluble arsenic melting point, 57 °C 67 g in 100 mL at 20 °C
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98.0–102.0% Na2HAsO4 · 7H2O Maximum Allowable Insoluble matter . . . . . . . . . . . . . . . . . . . . . 0.005% Arsenite (As2O3) . . . . . . . . . . . . . . . . . . . . . 0.01% Chloride (Cl) . . . . . . . . . . . . . . . . . . . . . . . 0.001% Nitrate (NO3) . . . . . . . . . . . . . . . . . . . . . . . 0.005% Sulfate (SO4) . . . . . . . . . . . . . . . . . . . . . . . 0.01% Heavy metals (as Pb) . . . . . . . . . . . . . . . . . . 0.002% Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 0.001%
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4328 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
TESTS Assay (By titration of oxidizing power of arsenate). Weigh accurately about 0.55 g, and dissolve in 50 mL of water in a glassstoppered conical flask. Heat to 80 °C, and add 10 mL of hydrochloric acid and 3 g of potassium iodide. Stopper the flask, swirl, and maintain at 80 °C for 15 min. Cool to room temperature, and titrate the liberated iodine with 0.1 N sodium thiosulfate volumetric solution, adding 3 mL of starch indicator solution near the end of the titration. One milliliter of 0.1 N sodium thiosulfate corresponds to 0.01560 g of Na2HAsO4 · 7H2O.
Insoluble Matter [Part 2: Gravimetric Methods; Insoluble Matter]. Use 20 g dissolved in 200 mL of water.
Arsenite Dissolve 10 g in 75 mL of water, make the solution just acidic to litmus paper with 10% sulfuric acid, and add 2 g of sodium bicarbonate. When dissolution is complete, add starch indicator solution, and titrate with 0.02 N iodine to a blue end point. Not more than 1.0 mL of 0.02 N iodine should be required.
Chloride [Part 2: Colorimetry and Turbidimetry; Chloride]. Use 1.0 g of sample and 5 mL of nitric acid.
Nitrate [Part 2: Colorimetry and Turbidimetry; Nitrate; Procedure for Nitrate, Method 1 (Brucine Sulfate)].
For the Determination of Nitrate
S a m p l e S o l u t i o n A . Dissolve 0.20 g in 3 mL of water by heating on a hot plate (~100 °C). Dilute to 50 mL with brucine sulfate reagent solution. C o n t r o l S o l u t i o n B . Dissolve 0.20 g in 2 mL of water and 1 mL of nitrate ion (NO3) standard solution by heating on a hot plate (~100 °C). Dilute to 50 mL with brucine sulfate reagent solution.
Continue with the procedure, starting with the preparation of blank solution C.
Sulfate Dissolve 10 g in 10 mL of water, add 5 mL of hydrochloric acid, and heat the solution to boiling. Add 5 mL of 12% barium chloride reagent solution, digest in a covered beaker on a hot plate (~100 °C) for 2 h, and allow to stand for at least 8 h. If any precipitate is formed, filter, wash thoroughly, and ignite. Correct for the weight obtained in a complete blank test.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4328 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Heavy Metals [Part 2: Colorimetry and Turbidimetry; Heavy Metals (as Lead); Procedure for Heavy Metals, Method 1]. Dissolve 2.5 g in 20 mL of water in a small dish. Add 2 g of potassium iodide, 10 mL of hydrobromic acid, and 0.10 mL of sulfuric acid. Evaporate to dryness on a hot plate (~100 °C), wash down the sides of the dish with a few milliliters of water, add 5 mL of hydrochloric acid, and again evaporate to dryness on a hot plate (~100 °C). Dissolve the residue in a few milliliters of water, neutralize to litmus paper with 10% ammonium hydroxide reagent solution, and dilute with water to 50 mL. Use 30 mL to prepare the sample solution, and use 10 mL of the remaining solution to prepare the control solution.
Iron [Part 2: Colorimetry and Turbidimetry; Iron; Procedure for Iron, Method 1 (Ammonium Thiocyanate)]. Use 1.0 g of sample and 5 mL of hydrochloric acid.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4328 ACS Reagent Chemicals, Part 4
