Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Potassium Hydrogen Phthalate, Acidimetric Standard (Potassium Acid Phthalate; Potassium Biphthalate; Phthalic Acid, Monopotassium Salt) 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 Hydrogen Phthalate, Acidimetric Standard provides, in addition to common physical constants, a general description including typical appearance, applications, change in state (approximate), aqueous solubility, and density. The monograph also details the following specifications, corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay, pH of a 0.05 M Solution, Insoluble Matter, Chlorine Compounds, Sulfur Compounds, Heavy Metals, Iron, and Sodium. Special caution is advised for the handling or testing of this substance.
HOCOC6H4COOK
Formula Wt 204.22
CAS No. 877-24-7
Note: This reagent is satisfactory for use as a pH standard. For use as an acidimetric standard, this material should be lightly crushed and dried for 2 h at 120 °C to remove any absorbed moisture.
GENERAL DESCRIPTION Typical appearance . . . . . . . . Applications . . . . . . . . . . . . . Change in state (approximate) . Aqueous solubility . . . . . . . . . Density . . . . . . . . . . . . . . . .
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© 2017 American Chemical Society
white solid acidimetric standard melting point, 295 °C, with decomposition 10 g in 100 mL at 25 °C 1.64
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DOI:10.1021/acsreagents.4291 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
SPECIFICATIONS Assay (dried basis). . . . . . . . . . . . . . . . . . . . 99.95–100.05% C8H5O4K pH of a 0.05 M solution. . . . . . . . . . . . . . . . . 4.00–4.02 at 25.0 ± 0.2 °C
Insoluble matter . . . . . . . . Chlorine compounds (as Cl) . Sulfur compounds (as S) . . . Heavy metals (as Pb) . . . . . Iron (Fe) . . . . . . . . . . . . . Sodium (Na) . . . . . . . . . . .
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Maximum Allowable 0.005% 0.003% 0.002% 5 ppm 5 ppm 0.005%
TESTS Assay (By acid–base titrimetry). This is a comparative procedure in which the potassium hydrogen phthalate to be assayed is compared with NIST SRM potassium hydrogen phthalate. Accurately weighed portions of anhydrous sodium carbonate, dissolved in water, are allowed to react with accurately weighed portions of the two potassium hydrogen phthalate samples of such size as to provide a small excess of the potassium hydrogen phthalate. The carbon dioxide is removed by boiling and the excess potassium hydrogen phthalate is determined by titration with carbonate-free sodium hydroxide using a potentiometric end point. C a u t i o n : Due to the small tolerance in assay limits for this acidimetric standard, extreme care must be observed in the weighing, transferring, and titrating operations in the following procedure. Strict adherence to the specified sample weights and final titration volumes is absolutely necessary. It is recommended that the titrations be run at least in duplicate on both the sample and the SRM. Duplicate values of M, the number of milliequivalents of total alkali required per gram of potassium hydrogen phthalate, obtained on the sample and on the SRM, should agree within 2 parts in 5000 to be acceptable for averaging.
Pr o c e d u r e . Place duplicate 1.300 ± 0.001 g portions of a uniform sample of anhydrous sodium carbonate in clean, dry weighing bottles. Dry at 285 °C for 3 h, stopper the bottles, and cool in a desiccator for at least 2 h. Open the weighing bottles momentarily to equalize the pressure, weigh each bottle and its contents to the nearest 0.1 mg, and transfer the entire contents of each bottle to a clean, dry 50 mL beaker. Store the beaker in a desiccator until ready for use, weigh each bottle again, and determine by difference, to the nearest 0.1 mg, the weight of each portion of sodium carbonate. Transfer the portions of sodium carbonate to 500 mL titration flasks by pouring them through powder funnels. Rinse the beakers, funnels, and sides of the flasks thoroughly with several small portions of water. In the same manner, add to one of these flasks 5.100 ± 0.003 g of the potassium hydrogen phthalate to be assayed and to the other flask the same weight of the NIST SRM potassium hydrogen phthalate—both of which have been previously crushed (not ground) in an agate or mullite mortar to approximately 100 mesh fineness, dried at 120 °C for 2 h, and cooled in a desiccator for at least 2 h. Dilute the contents of each titration flask with water to about 90 mL, swirl to dissolve the samples, stopper, and bubble carbon dioxide-free air through the solutions at a moderately fast rate during all subsequent operations. Boil the solutions gently for 20 min to complete the removal of carbon dioxide, taking care to prevent loss of solutions by spraying. Cool the solutions to room temperature in an ice bath, and dilute to 75–80 mL with carbon dioxide-free water. Titrate each solution with 0.02 N carbonate-free sodium hydroxide using a combination electrode (glass–calomel or glass–silver, silver chloride) for the measurement of E in millivolts or pH. The end point of the titration is determined by the second derivative method [Part 2: Titrimetric Methods; Potentiometric Titrations; Second Derivative Method for Determination of Equivalence Point].
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4291 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
C a l c u l a t i o n s . Calculate the number of milliequivalents of total alkali (sodium carbonate plus sodium hydroxide) required to neutralize exactly 1 g of the sample of potassium hydrogen phthalate and of the NIST SRM by the following equations:
where Mu = number of meq of total alkali required per g of potassium hydrogen phthalate being assayed; Ms = number of meq of total alkali required per g of NIST standard potassium hydrogen phthalate; B = weight, in g, of sodium carbonate; C = volume, in mL, of sodium hydroxide standard solution; D = normality of sodium hydroxide standard solution; Wu = weight, in g, of potassium hydrogen phthalate being assayed; Ws = weight, in g, of NIST SRM potassium hydrogen phthalate; and F = assay value of NIST SRM in percent divided by 100. Calculate the assay value of the sample of potassium hydrogen phthalate as follows:
where A is percent of potassium hydrogen phthalate in the sample assayed and Mu and Ms are defined as before.
pH of a 0.05 M Solution Dissolve 1.021 g in 100 g of carbon dioxide- and ammonia-free water (or 1.012 g in a volume of 100 mL). Standardize the pH meter and electrodes at pH 4.00 at 25.0 ± 0.2 °C with 0.05 M NIST SRM potassium hydrogen phthalate. Determine the pH of the solution by the method described in [Part 2: Measurement of Physical Properties; Melting Point] for pH of buffer standard solutions. The pH should be 4.00–4.02 at 25.0 ± 0.2 °C.
Insoluble Matter [Part 2: Gravimetric Methods; Insoluble Matter]. Use 20 g dissolved in 200 mL of water.
Chlorine Compounds Mix 1.0 g with 0.5 g of sodium carbonate in a platinum vessel, moisten the mixture, and ignite until thoroughly charred, avoiding an unduly high temperature. Treat the residue with 30 mL of water, cautiously add 3 mL of nitric acid, and filter through a chloride-free filter. Wash the residue with a few milliliters of hot water, dilute the filtrate with water to 50 mL, and to 25 mL of the filtrate add 1 mL of silver nitrate reagent solution. Any turbidity should not exceed that produced by 0.015 mg of chloride ion (Cl) in an equal volume of solution containing the quantities of reagents used in the test.
Sulfur Compounds Mix 2.0 g with 1 g of sodium carbonate, add in small portions 15 mL of water, evaporate, and thoroughly ignite, taking care to protect the sample from the flame because of the presence of sulfur compounds in the natural gas. Treat the residue with 20 mL of water and 2 mL of 30% hydrogen peroxide, and heat on a hot plate (~100 °C) for 15 min. Add 5 mL of hydrochloric acid, and evaporate to dryness on the hot plate. Dissolve the residue in 10 mL of water, filter, wash with several portions of water, and dilute the filtrate with water to 25 mL. Add to this solution 0.5 mL of 1 N hydrochloric acid and 2 mL of 12% barium chloride reagent solution. Any turbidity should not exceed that in a standard prepared as follows: Treat 1 g of sodium carbonate with 2 mL of 30% hydrogen peroxide and 5 mL of hydrochloric acid, and evaporate to dryness on a hot plate (~100 °C). Dissolve the residue and 0.12 mg of sulfate ion (SO4)in sufficient water to make 25mL, and add 0.5 mL of 1 N hydrochloric acid and 2 mL of 12% barium chloride reagent solution.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4291 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 6.6 g in warm water, and dilute with water to 50 mL. Use 40 mL to prepare the sample solution, and use the remaining 10 mL to prepare the control solution.
Iron [Part 2: Colorimetry and Turbidimetry; Iron; Procedure for Iron, Method 2 (Hydroxylamine and 1,10-Phenanthroline)]. For the test, use 2.0 g, dissolve in 30 mL of water, and dilute to 50 mL.
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 1.0 g of sample in water, and dilute to 100 mL in a volumetric flask with water (1 mL = 0.01 g).
For the Determination of Sodium
Element
Wavelength (nm)
Sample Wt (g)
Standard Added (mg)
Flame Type*
Background Correction
Na
589.0
0.20
0.01; 0.02
A/A
No
*A/A is air/acetylene.
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DOI:10.1021/acsreagents.4291 ACS Reagent Chemicals, Part 4
