Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Oxalic Acid Dihydrate (Ethanedioic Acid Dihydrate) 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 Oxalic Acid Dihydrate provides, in addition to common physical constants, a general description including typical appearance, applications, change in state (approximate), aqueous solubility, density, and pKa. The monograph also details the following specifications and corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay, Substances Darkened by Hot Sulfuric Acid, Insoluble Matter, Residue after Ignition, Chloride, Sulfate, Calcium, Nitrogen Compounds, Heavy Metals, and Iron.
H2C2O4 • 2H2O
Formula Wt 126.07
CAS No. 6153-56-6
GENERAL DESCRIPTION Typical appearance . . . . . . . . Applications . . . . . . . . . . . . . Change in state (approximate) . Aqueous solubility . . . . . . . . . Density . . . . . . . . . . . . . . . . pKa . . . . . . . . . . . . . . . . . .
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white or colorless solid reducing agent; precipitant for certain metals melting point, hydrated acid, 101 °C; anhydrous acid, 189 °C 14 g in 100 mL at 20 °C 1.65 1.3
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99.5–102.5% H2C2O4 · 2H2O Substances darkened by hot sulfuric acid . . . . . Passes test Maximum Allowable Insoluble matter . . . . . . . . . . . . . . . . . . . . . 0.005% Residue after ignition. . . . . . . . . . . . . . . . . . 0.01%
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4251 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Chloride (Cl) . . . . . . . . . Sulfate (SO4) . . . . . . . . . Calcium (Ca) . . . . . . . . . Nitrogen compounds (as N) Heavy metals (by ICP–OES) Iron (Fe) . . . . . . . . . . . .
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0.002% 0.005% 0.001% 0.001% 5 ppm 2 ppm
TESTS Assay (By titration of reductive capacity). Weigh accurately 0.25 g, and add 50 mL of water and 5 mL of sulfuric acid. Titrate slowly with 0.1 N potassium permanganate volumetric solution until about 25 mL has been added. Heat the solution to about 70 °C, and complete the titration to a permanent faint pink color. One milliliter of 0.1 N potassium permanganate corresponds to 0.006303 g of H2C2O4 · 2H2O.
Substances Darkened by Hot Sulfuric Acid Dissolve 2.0 g in 20 mL of sulfuric acid, and heat at 150 °C for 30 min. Any color should not exceed that produced in a color standard of the following composition: 0.2 mL of cobalt chloride reagent solution, 1.0 mL of ferric chloride reagent solution, and 0.2 mL of cupric sulfate reagent solution, in 20 mL of water.
Insoluble Matter [Part 2: Gravimetric Methods; Insoluble Matter]. Use 20.0 g dissolved in 250 mL of water.
Residue after Ignition [Part 2: Gravimetric Methods; Residue after Ignition]. Dry 10.0 g in a tared, preconditioned crucible or dish for 1 h at 105 °C, slowly ignite, and continue as described. Retain the residue for the test for iron.
Chloride [Part 2: Colorimetry and Turbidimetry; Chloride]. Dissolve 0.5 g in 20 mL of nitric acid.
Sulfate Digest 1.0 g of sample with 1 mL of 1% sodium carbonate reagent solution, 3 mL of 30% hydrogen peroxide, and 0.5 mL of nitric acid in a covered beaker on a hot plate (~100 °C) until reaction ceases. Remove the cover, and evaporate to dryness. Dissolve the residue in 6 mL of dilute hydrochloric acid (1:1), and again evaporate to dryness. Dissolve the residue in 4 mL of water plus 1 mL of dilute hydrochloric acid (1:19), filter if necessary through a small filter, wash the precipitate with two 2 mL portions of water, and dilute with water to 10 mL. Add 1 mL of 12% barium chloride reagent solution. Any turbidity should not exceed that produced when a solution containing 0.05 mg of sulfate ion (SO4) is treated exactly like the 1.0 g of sample. Compare 10 min after adding the barium chloride to the sample and standard solutions.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4251 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Calcium (By flame AAS, [Part 2: Trace and Ultratrace Elemental Analysis; Atomic Absorption Spectroscopy; Analysis; Procedure for Flame AAS]).
For the Determination of Calcium
S a m p l e S t o c k S o l u t i o n . Suspend 10.0 g of sample in 50 mL of nitric acid (1:24), and add 25 mL of 30% hydrogen peroxide. Cover, and digest on a hot plate (~100 °C) until the reaction ceases. Add 5 mL more of the hydrogen peroxide, and when the reaction ceases, uncover and evaporate to dryness. Dissolve the residue in 80 mL of nitric acid (1:99), transfer to a 100 mL volumetric flask, and dilute to the mark with nitric acid (1:99) (1 mL = 0.10 g).
For the Determination of Calcium
Element
Wavelength (nm)
Sample Wt (g)
Standard Added (mg)
Flame Type*
Background Correction
Ca
422.7
2.0
0.02; 0.04
N/A
No
*N/A is nitrous oxide/acetylene.
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).
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 2.0 g sample.
Iron [Part 2: Colorimetry and Turbidimetry; Iron; Procedure for Iron, Method 1 (Ammonium Thiocyanate)]. To the residue after ignition, add 3 mL of dilute hydrochloric acid (1:1), cover with a watch glass, and digest on a hot plate (~100 °C) for 15 min. Remove the cover, and evaporate to dryness. Dissolve the residue in 2 mL of dilute hydrochloric acid (1:1), add about 40 mL of water, filter if necessary, and dilute with water to 50 mL. Use 25.0 mL (5.0 g) of the solution.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4251 ACS Reagent Chemicals, Part 4
