Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Phosphoric Acid, Meta(Vitreous Sodium Acid Metaphosphate) 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 Phosphoric Acid, Meta- provides, in addition to common physical constants, a general description including typical appearance, applications, aqueous solubility, and pKa. The monograph also details the following specifications and corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay, Stabilizer, Nitrate, Sulfate, Chloride, Arsenic, Heavy Metals, Iron, and Substances Reducing Permanganate.
CAS No. 37267-86-0
Note: This reagent contains as a stabilizer a somewhat greater proportion of sodium metaphosphate than that corresponding to the empirical formula NaH(PO3)2.
GENERAL DESCRIPTION Typical appearance Applications . . . . . Aqueous solubility . pKa . . . . . . . . . .
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transparent, glass-like solid or very silky masses; hygroscopic acid digestion very slowly soluble in cold water, slowly changing to H3PO4 2.1
SPECIFICATIONS Assay (HPO3) . . . . . . . . . . . . . . . . . . . . . . . 33.5–36.5% Stabilizer (NaPO3) . . . . . . . . . . . . . . . . . . . . 57.0–63.0% Maximum Allowable Nitrate (NO3) . . . . . . . . . . . . . . . . . . . . . . . 0.001% Sulfate (SO4) . . . . . . . . . . . . . . . . . . . . . . . 0.005% Chloride (Cl) . . . . . . . . . . . . . . . . . . . . . . . 0.001% Arsenic (As) . . . . . . . . . . . . . . . . . . . . . . . . 1 ppm Heavy metals (as Pb) . . . . . . . . . . . . . . . . . . 0.005%
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4268 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 0.005% Substances reducing permanganate (as H3PO3) . . 0.02%
TESTS Assay (By alkalimetry). Weigh accurately about 5.0 g. In a suitable flask, dissolve in 400 mL of water, and titrate with 1 N sodium hydroxide volumetric solution to a pH of 4.4 (using a pH meter). One milliliter of 1 N sodium hydroxide corresponds to 0.07998 g of metaphosphoric acid (HPO3).
Stabilizer Weigh accurately 20.0 g, dissolve in water, and dilute with water to 1 L. To 50.0 mL of this solution in a 200 mL volumetric flask, add 50 mL of water and 50 mL of a 10% lead acetate reagent solution, dilute with water to 200 mL, mix thoroughly, and decant through a filter. Treat 100 mL of the clear filtrate with freshly prepared hydrogen sulfide water sufficiently to precipitate the excess of lead, filter, and wash with about 20 mL of water. To the filtrate, add 2 mL of sulfuric acid, evaporate to dryness in a tared, preconditioned dish, and ignite to constant weight at 600 ± 25 °C. Calculate the weight of NaPO3 by multiplying the weight of sodium sulfate by the factor 1.4356.
Nitrate [Part 2: Colorimetry and Turbidimetry; Nitrate; Procedure for Nitrate, Method 1 (Brucine Sulfate)]. For sample solution A, use 1.0 g in 4 mL of water. For control solution B, use 1.0 g and 1 mL of nitrate ion (NO3) standard solution.
Sulfate Dissolve 8.0 g in 180 mL of water, heat the solution to boiling, cool, filter, and heat again to boiling. Add 10 mL of 40% 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 a precipitate is formed, filter, wash thoroughly, and ignite. The weight of the precipitate should not be more than 0.001 g greater than the weight obtained in a complete blank test, including filtration of a solution of 2 mL of hydrochloric acid in 200 mL of water.
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For the Determination of Chloride, Arsenic, Heavy Metals, Iron, and Substances Reducing Permanganate
S a m p l e S o l u t i o n A . Dissolve 20 g in 150 mL of water, cool, and dilute with water to 200 mL (1 mL = 0.1 g).
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4268 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
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Chloride
[Part 2: Colorimetry and Turbidimetry; Chloride]. Dilute 10 mL of sample solution A (1 g sample) with water to 25 mL, and add 0.5 mL of nitric acid.
Arsenic† [Part 2: Colorimetry and Turbidimetry; Arsenic]. Dilute 30 mL of sample solution A (3 g sample) with water to 35 mL. For the standard, use 0.003 mg of arsenic.
Heavy Metals† To 50 mL of sample solution A (5 g sample), add 0.15 mL of phenolphthalein indicator solution, and neutralize with ammonium hydroxide. Adjust the pH of this solution to 4.5 (using a pH meter) with 1 N sulfuric acid and dilute with water to 250 mL. For the sample, use 40 mL of the solution. For the control, add 0.02 mg of lead to 20 mL of the solution, and dilute with water to 40 mL. Add 10 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.
Iron† To 2.0 mL of sample solution A (0.2 g sample), add 5 mL of water and 3 mL of hydrochloric acid, boil gently for 10 min, and cool. Add 3.5 mL of 0.5 N sodium acetate, 6 mL of hydroxylamine hydrochloride reagent solution, and 4 mL of 1,10phenanthroline reagent solution. Adjust the pH to between 4 and 6 with ammonium hydroxide. Any red color produced within 1 h should not exceed that produced by 0.01 mg of iron in an equal volume of solution containing the quantities of reagents used in the test.
Substances Reducing Permanganate† To 50 mL of sample solution A (5 g sample), add 10 mL of 10% sulfuric acid reagent solution, heat the solution to boiling, and titrate with 0.1 N potassium permanganate volumetric solution to a pink color that remains for 5 min. Not more than 0.25 mL of permanganate should be required.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4268 ACS Reagent Chemicals, Part 4
