Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Chromium Potassium Sulfate Dodecahydrate (Chromium(III) Potassium Sulfate Dodecahydrate) 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 Chromium Potassium Sulfate Dodecahydrate 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, Chloride, Aluminum, Iron, Ammonium, and Heavy Metals.
CrK(SO4)2·12H2O
Formula Wt 499.39
CAS No. 7788-99-0
GENERAL DESCRIPTION Typical appearance . . . . . . . . Applications . . . . . . . . . . . . . Change in state (approximate) . Aqueous solubility . . . . . . . . .
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violet solid preparation of chromium standard solutions melting point, 89 °C 20 g in 100 mL cold water
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98.0–102.0% as CrK(SO4)2 · 12H2O Maximum Allowable Insoluble matter . . . . . . . . . . . . . . . . . . . . . 0.01% Chloride (Cl) . . . . . . . . . . . . . . . . . . . . . . . 0.002% Aluminum (Al) . . . . . . . . . . . . . . . . . . . . . . 0.02% Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 0.01% Ammonium (NH4) . . . . . . . . . . . . . . . . . . . . 0.01% Heavy metals (as Pb) . . . . . . . . . . . . . . . . . . 0.01%
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4093 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
TESTS Assay (By iodometric titration for oxidative capacity of CrVI). Weigh accurately about 0.65 g, and transfer to a 500 mL iodine flask with 50 mL of water. Add 5 mL of 30% hydrogen peroxide and 15 mL of 10% sodium hydroxide reagent solution. Dilute with 100 mL of water, and boil until the solution color is yellow. Add dropwise 5 mL of 5% aqueous nickel sulfate hexahydrate solution. When the vigorous evolution of oxygen has ceased, boil for 3 min and cool. Add 1.0 g of potassium iodide and 5 mL each of phosphoric and hydrochloric acids. Mix well, and titrate the liberated iodine with 0.1 N sodium thiosulfate, adding 3 mL of starch indicator solution near the end of the titration. One milliliter of 0.1 N sodium thiosulfate corresponds to 0.01665 g of CrK(SO4)2 · 12H2O.
Insoluble Matter [Part 2: Gravimetric Methods; Insoluble Matter]. Use 10 g dissolved in 100 mL of water.
Chloride Dissolve 1.0 g in 10 mL of water, heat the solution to boiling, and add 2 mL of ammonium hydroxide to the hot, constantly stirred solution. Boil gently to expel excess ammonia, filter through a small chloride-free filter, wash with hot water until the volume of filtrate and washings is about 45 mL, dilute with water to 50 mL, and mix. To 25 mL of this solution, add 1.5 mL of nitric acid and 1 mL of silver nitrate reagent solution. Any turbidity should not exceed that produced by 0.01 mg of chloride ion (Cl) in an equal volume of solution containing the quantities of reagents used in the test.
Aluminum and Iron (By flame AAS, [Part 2: Trace and Ultratrace Elemental Analysis; Atomic Absorption Spectroscopy; Analysis; Procedure for Flame AAS]).
For the Determination of Aluminum and Iron
S a m p l e S t o c k S o l u t i o n . Dissolve 20.0 g of sample in 60 mL of water, transfer to a 100 mL volumetric flask, and dilute to the mark with water (1 mL = 0.2 g).
For the Determination of Aluminum and Iron
Element
Wavelength (nm)
Sample Wt (g)
Standard Added (mg)
Flame Type*
Background Correction
Al
309.3
4.0
0.40; 0.80
N/A
Yes
Fe
248.3
4.0
0.20; 0.40
A/A
Yes
*A/A is air/acetylene; N/A is nitrous oxide/acetylene.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4093 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Ammonium (By colorimetry, [Part 2: Colorimetry and Turbidimetry; Ammonium (Test for Ammonia and Amines)]). Dilute the distillate from a 1.0 g sample with water to 50 mL, and use 5 mL of the dilution. For the standard, use 0.01 mg of ammonium ion (NH4).
Heavy Metals [Part 2: Colorimetry and Turbidimetry; Heavy Metals (as Lead); Procedure for Heavy Metals, Method 1]. Dissolve 1.0 g with 30 mg of mercuric chloride in 40 mL of water. Add 15 mL of hydrogen sulfide water, stir, and allow to stand for 30 min. Filter and wash thoroughly with hydrogen sulfide water containing 1% potassium sulfate. Ignite the precipitate at low temperature in a small porcelain dish in a well-ventilated hood to char the paper, then at 525 ± 25 °C for 30 min. To the residue, add 1 mL of hydrochloric acid, 1 mL of nitric acid, and about 30 mg of sodium carbonate, and evaporate to dryness on a hot plate (~100 °C). Dissolve the residue in about 20 mL of water, and dilute with water to 100 mL. Use 20 mL to prepare the sample solution.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4093 ACS Reagent Chemicals, Part 4
