Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Chromotropic Acid, Disodium Salt (4,5-Dihydroxy-2,7-naphthalenedisulfonic Acid, Disodium 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 Chromotropic Acid, Disodium Salt 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: Clarity of Solution, Sensitivity to Nitrate, and Sensitivity to Formaldehyde.
(HO)2C10H4(SO3Na)2·2H2O Formula Wt 400.28 (disodium salt) 4,5-(OH)2C10H4-2,7Formula Wt 320.29 (SO3H)2 (free acid)
CAS No. 5808-22-0 CAS No. 148-25-4
Note: Two forms of this reagent are available: the disodium salt dihydrate and the free acid. This specification applies to both forms, but the sample weight of the acid should be changed to 80% of that for the salt.
GENERAL DESCRIPTION Typical appearance . . . . . . . . Applications . . . . . . . . . . . . . Change in state (approximate) . Aqueous solubility . . . . . . . . .
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© 2017 American Chemical Society
tan to brown solid determination of nitrate and formaldehyde melting point, 300 °C very soluble
A
DOI:10.1021/acsreagents.4095 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
SPECIFICATIONS Clarity of solution . . . . . . . . . . . . . . . . . . . . Passes test Sensitivity to nitrate . . . . . . . . . . . . . . . . . . Passes test Sensitivity to formaldehyde . . . . . . . . . . . . . . Passes test
TESTS Clarity of Solution Use 5.0 g of the salt or 4.0 g of the acid dissolved in 100 mL of hot water. Add a few drops of 10% sodium hydroxide reagent solution if necessary. The solution should be free of turbidity.
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For the Determination of Sensitivities to Nitrate and Formaldehyde
S a m p l e S o l u t i o n A . Dissolve 0.20 g of the salt (0.16 g of the acid) in 100 mL of sulfuric acid.
Sensitivity to Nitrate† Into three 50 mL volumetric flasks, pipette 1.0, 2.0, and 3.0 mL of a nitrate ion (NO3) standard solution. For the blank, add 1.0 mL of water to another 50 mL volumetric flask. To each flask, add approximately 5 mL of sulfuric acid, swirl, and cool in an ice bath. Add 2.0 mL of sample solution A to each flask, swirl again, and cool. Dilute to 50 mL with sulfuric acid, and shake well. Set a spectrophotometer at 410 nm, and using 5 cm cells, determine the absorbance of the standard solutions against the blank. A plot of absorbance versus concentration of nitrate should be linear, with a minimum absorbance of 0.20 for the solution containing 0.03 mg of nitrate.
Sensitivity to Formaldehyde† Into three 50 mL volumetric flasks, pipette 1.0, 2.0, and 3.0 mL of formaldehyde II standard solution. For the blank, add 1.0 mL of water to another 50 mL volumetric flask. To each flask, add 5.0 mL of sample solution A, stopper, and shake. Dilute to the mark with sulfuric acid and let stand in a hot water bath (70–80 °C) for 15 min. Cool in an ice bath to room temperature, fill to volume with sulfuric acid, stopper, and shake. Set a spectrophotometer at 580 nm, and using 1 cm cells, determine the absorbance of the standard solutions against the blank. A plot of absorbance versus concentration of formaldehyde should be linear, with a minimum absorbance of 0.30 for the solution containing 0.03 mg of formaldehyde.
© 2017 American Chemical Society
B
DOI:10.1021/acsreagents.4095 ACS Reagent Chemicals, Part 4
