Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Sodium Phosphate, Dibasic, Heptahydrate (Disodium Hydrogen Phosphate 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 Phosphate, Dibasic, Heptahydrate provides, in addition to common physical constants, a general description including typical appearance, applications, 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, pH of a 5% Solution at 25.0 °C, Insoluble Matter, Chloride, Sulfate, Heavy Metals, and Iron.
Na2HPO4 • 7H2O
Formula Wt 268.07
CAS No. 7782-85-6
GENERAL DESCRIPTION Typical appearance . . . . . . . . . . . . . . . . . . . colorless or white solid Applications . . . . . . . . . . . . . . . . . . . . . . . . buffering agent Aqueous solubility . . . . . . . . . . . . . . . . . . . . soluble in 4 parts of water
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98.0–102.0% Na2HPO4 · 7H2O pH of a 5% solution at 25.0 °C . . . . . . . . . . . . 8.7–9.3 Maximum Allowable Insoluble matter . . . . . . . . . . . . . . . . . . . . . 0.005% Chloride (Cl) . . . . . . . . . . . . . . . . . . . . . . . 0.001% Sulfate (SO4) . . . . . . . . . . . . . . . . . . . . . . . 0.005% Heavy metals (by ICP–OES) . . . . . . . . . . . . . . 0.001% Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 0.001%
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4364 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
TESTS Assay (By indirect acid–base titrimetry). Weigh accurately about 10.5 g, and dissolve in 50 mL of water and exactly 50.0 mL of 1 N hydrochloric acid volumetric solution. Titrate the excess acid with 1 N sodium hydroxide volumetric solution to the first inflection point at about pH 4, as measured with a pH meter. Calculate A, the equivalent of 1 N hydrochloric acid consumed by the sample. Continue the titration with 1 N sodium hydroxide volumetric solution to the second inflection point at about pH 8.8. Calculate B, the equivalent of 1 N sodium hydroxide required in the titration between the two inflection points.
If A is equal to or less than B, then
If A is greater than B, then
pH of a 5% Solution at 25.0 °C [Part 2: Direct Electrometric Methods; pH Potentiometry; pH Range; Procedure for pH of a 5% Solution at 25.0 °C].
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 1.0 g of sample and 3 mL of nitric acid.
Sulfate Dissolve 1.0 g in 15 mL of water, and add 2.5 mL of 10% hydrochloric acid (solution approximately pH 2). Filter through washed filter paper, and add 10 mL of water through the same filter. For the control, add 0.05 mg of sulfate ion (SO4) in 20 mL of water, and add 1.0 mL of (1:19) hydrochloric acid. Dilute both to 35 mL with water, add 5.0 mL of 40% barium chloride solution, and mix. Observe turbidity after 10 min. Sample solution turbidity should not exceed that of the control solution.
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.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4364 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Iron [Part 2: Colorimetry and Turbidimetry; Iron; Procedure for Iron, Method 2 (Hydroxylamine and 1,10-Phenanthroline)]. Use 1.0 g.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4364 ACS Reagent Chemicals, Part 4
