Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Potassium Phosphate, Dibasic (Dipotassium Hydrogen Phosphate) 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 Potassium Phosphate, Dibasic 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, Loss on Drying, Chloride, Nitrogen Compounds, Sulfate, Heavy Metals, Iron, and Sodium.
K2HPO4
Formula Wt 174.17
CAS No. 7758-11-4
GENERAL DESCRIPTION Typical appearance . . . . . . . . . . . . . . . . . . . white solid Applications . . . . . . . . . . . . . . . . . . . . . . . . buffer solutions Aqueous solubility . . . . . . . . . . . . . . . . . . . . very soluble
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . ≥98.0% K2HPO4 pH of a 5% solution at 25.0 °C . . . . . . . 8.5–9.6 Maximum Allowable Insoluble matter . . . . . . . . . . . . . . . . . . . . . 0.01% Loss on drying . . . . . . . . . . . . . . . . . . . . . . 1.0% Chloride (Cl) . . . . . . . . . . . . . . . . . . . . . . . 0.003% Nitrogen compounds (as N) . . . . . . . . . . . . . . 0.001% Sulfate (SO4) . . . . . . . . . . . . . . . . . . . . . . . 0.005% Heavy metals (by ICP–OES) . . . . . . . . . . . . . . 5 ppm Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 0.001% Sodium (Na) . . . . . . . . . . . . . . . . . . . . . . . . 0.05%
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4304 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 7.0 g of sample, 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 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:
If A is greater than B:
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 10 g dissolved in 100 mL of water.
Loss on Drying Weigh accurately about 2 g. Dry in a tared, preconditioned vessel, at 105 °C to constant weight.
Chloride [Part 2: Colorimetry and Turbidimetry; Chloride]. Use 0.33 g.
Nitrogen Compounds [Part 2: Colorimetry and Turbidimetry; Nitrogen Compounds: Test for Ammonia, Amines, and Nitrogen Compounds Reduced by Aluminum]. Use 1.0 g. For the standard, use 0.01 mg of nitrogen ion (N).
Sulfate Dissolve 1.0 g in 15 mL of water, and add 4.0 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 sample and control solutions to 35 mL with water, add
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4304 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
5.0 mL of 40% barium chloride reagent solution to each, 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.
Iron [Part 2: Colorimetry and Turbidimetry; Iron; Procedure for Iron, Method 2 (Hydroxylamine and 1,10-Phenanthroline)]. Use 1.0 g.
Sodium (By flame AAS, [Part 2: Trace and Ultratrace Elemental Analysis; Atomic Absorption Spectroscopy; Analysis; Procedure for Flame AAS]).
For the Determination of Sodium
S a m p l e S t o c k S o l u t i o n . Dissolve 2.0 g of sample in a 100 mL volumetric flask and dilute to the mark with water (1 mL = 0.02 g).
For the Determination of Sodium
Element
Wavelength (nm)
Sample Wt (g)
Standard Added (mg)
Flame Type*
Background Correction
Na
589.0
0.02
0.01; 0.02
A/A
No
*A/A is air/acetylene.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4304 ACS Reagent Chemicals, Part 4
