Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Chromium Trioxide (Chromium(VI) Oxide) 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 Trioxide 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, Nitrate, Sulfate, Aluminum, Barium, Iron, and Sodium.
CrO3
Formula Wt 100.00
CAS No. 1333-82-0
GENERAL DESCRIPTION Typical appearance . . . . . . . . Applications . . . . . . . . . . . . . Change in state (approximate) . Aqueous solubility . . . . . . . . .
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dark red or almost-black solid oxidizing agent in organic chemistry melting point, 197 °C 167 g in 100 mL at 20 °C
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . ≥98.0% CrO3 Maximum Allowable Insoluble matter . . . . . . . . . . . . . . . . . . . . . 0.01% Chloride (Cl) . . . . . . . . . . . . . . . . . . . . . . . 0.005% Nitrate (NO3) . . . . . . . . . . . . . . . . . . . . . . . 0.05% Sulfate (SO4) . . . . . . . . . . . . . . . . . . . . . . . 0.005% Aluminum (Al) . . . . . . . . . . . . . . . . . . . . . . 0.02% Barium (Ba) . . . . . . . . . . . . . . . . . . . . . . . . 0.01% Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 0.02% Sodium (Na) . . . . . . . . . . . . . . . . . . . . . . . . 0.2%
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4094 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). Weigh accurately about 5 g, transfer to a 1 L volumetric flask, dissolve in water, dilute with water to volume, and mix thoroughly. Place a 25 mL aliquot of this solution in a glass-stoppered conical flask, and dilute with 100 mL of water. Add 5 mL of dilute sulfuric acid (1:1) and 3 g of potassium iodide, and allow to stand in the dark for 15 min. Dilute with 100 mL of water, and titrate the liberated iodine with 0.1 N sodium thiosulfate volumetric solution, adding 3 mL of starch indicator solution near the end of the titration. Correct for a complete blank. One milliliter of 0.1 N sodium thiosulfate corresponds to 0.003333 g of CrO3.
Insoluble Matter [Part 2: Gravimetric Methods; Insoluble Matter]. Use 10.0 g dissolved in 100 mL of water.
Chloride Dissolve 1.0 g in water, filter if necessary through a chloride-free filter, and dilute with water to 50 mL. To 10 mL of this solution, add 1.5 mL of ammonium hydroxide and 1 mL of silver nitrate reagent solution, mix, and add 2 mL of nitric acid. Any turbidity should not exceed that produced in a standard containing 1 mL of ammonium hydroxide, 1 mL of silver nitrate reagent solution, 2 mL of nitric acid, and 0.01 mg of added chloride ion (Cl). The comparison is best made by the general method for chloride in colored solutions, [Part 2: Colorimetry and Turbidimetry; Chloride].
Nitrate
For the Determination of Nitrate
S a m p l e S t o c k S o l u t i o n . Dissolve 1.0 g in about 20 mL of water. Add 10% sodium hydroxide reagent solution until the color of the solution just turns light yellow, then add 0.2 mL of glacial acetic acid to change the color to orange (pH about 6.0–6.5). Slowly add a solution of 5 g of lead acetate in about 10 mL of water, dilute to 50 mL with water, mix, and allow to stand for 15 min. Transfer to a 50 mL centrifuge tube, centrifuge, and decant through a filter. This solution must be clear and colorless. Note: Two filter papers may be required to obtain a clear, colorless filtrate. Use a Nessler tube to check.
S a m p l e S o l u t i o n A . Dissolve 0.1 g of mercuric acetate in 2.0 mL of sample stock solution plus 1.0 mL of water in a dry test tube. Add 0.05 g of urea, and shake to dissolve. Put the tube in an ice bath, and immediately, but slowly, add 7 mL of cold 0.01% chromotropic acid reagent solution while swirling. Keep the tube in the ice bath an additional 2–3 min, remove, and let stand for 30 min, swirling occasionally. C o n t r o l S o l u t i o n B . Dissolve 0.1 g of mercuric acetate in 2.0 mL of sample stock solution in a dry test tube. Add 1.0 mL of a solution containing 0.02 mg of nitrate ion (NO3) per mL, then add 0.05 g of urea, and shake to dissolve. Put the tube in an ice bath, and immediately, but slowly, add 7 mL of cold 0.01% chromotropic acid reagent solution while swirling. Keep the tube in the ice bath an additional 2–3 min, remove, and let stand for 30 min, swirling occasionally.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4094 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
B l a n k S o l u t i o n C . Dissolve 0.1 g of mercuric acetate in 3.0 mL of water in a dry test tube. Add 0.05 g of urea, shake to dissolve, and put the tube in an ice bath. Add 7 mL of cold 0.01% chromotropic acid reagent solution while swirling, remove from the bath, and let stand for 30 min. Transfer sample solution A, control solution B, and blank solution C to dry 15 mL centrifuge tubes, and centrifuge until the supernatant liquid is clear. Set a spectrophotometer at 405 nm, and using 1 cm cells, adjust the instrument to read zero (absorbance units) with blank solution C in the light path, then determine the absorbance of sample solution A. Adjust the instrument to read zero (absorbance units) with sample solution A in the light path and determine the absorbance of control solution B. The absorbance of sample solution A should not exceed that of control solution B.
Sulfate Dissolve 10.0 g in 350 mL of water, and add 5.0 g of sodium carbonate. Heat to boiling, and add 35 mL of a solution containing 1 g of barium chloride and 2 mL of hydrochloric acid in 100 mL of water. 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. Fuse the ignited precipitate with 1 g of sodium carbonate. Extract the fused mass with water, and filter out the insoluble residue. Add 5 mL of hydrochloric acid to the filtrate, dilute with water to about 200 mL, heat to boiling, and add 10 mL of alcohol. Digest on a hot plate (~100 °C) until the reduction of chromate is complete, as indicated by the change to a clear green or colorless solution. Neutralize the solution with ammonium hydroxide, and add 2 mL of hydrochloric acid. Heat to boiling, and add 10 mL of 12% 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. Filter, wash thoroughly, and ignite. Correct for the weight obtained in a complete blank test.
Aluminum, Barium, Iron, and Sodium (By flame AAS, [Part 2: Trace and Ultratrace Elemental Analysis; Atomic Absorption Spectroscopy; Analysis; Procedure for Flame AAS]).
For the Determination of Aluminum, Barium, Iron, and Sodium
S a m p l e S t o c k S o l u t i o n A . Dissolve 10.0 g of sample in about 75 mL of water, transfer to a 100 mL volumetric flask, dilute to the mark with water, and mix (1 mL = 0.10 g). S a m p l e S t o c k S o l u t i o n B . Transfer exactly 10.0 mL of sample stock solution A to a 100 mL volumetric flask, dilute to the mark with water, and mix (1 mL = 0.01 g).
For the Determination of Aluminum, Barium, Iron, and Sodium
Element
Wavelength (nm)
Sample Wt (g)
Standard Added (mg)
Flame Type*
Background Correction
Al
309.3
2.0
0.20; 0.40
N/A
No
Ba
553.6
2.0
0.10; 0.20
N/A
No
Fe
248.3
2.0
0.20; 0.40
A/A
No
Na
589.0
0.01
0.01; 0.02
A/A
No
*A/A is air/acetylene; N/A is nitrous oxide/air.
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DOI:10.1021/acsreagents.4094 ACS Reagent Chemicals, Part 4
