Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Phenol Red (Phenolsulfonphthalein; 4,4′-(3H-2,1-Benzoxathiol-3-ylidene)bisphenol S,S-Dioxide) 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 Phenol Red provides, in addition to common physical constants, a general description including typical appearance, applications, 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 and Visual Transition Interval.
C19H14O5S (sultone) Formula Wt 354.38 C19H13O5SNa (sodium salt) Formula Wt 376.36
CAS No. 143-74-8 CAS No. 34487-61-1
Note: This standard applies to both the sultone and the salt forms of this indicator.
GENERAL DESCRIPTION Typical appearance . . . . . . . . . . . . . . . . . . . bright red to dark red solid Applications . . . . . . . . . . . . . . . . . . . . . . . . indicator for acidimetry Aqueous solubility . . . . . . . . . . . . . . . . . . . . 1 g in 1300 mL
SPECIFICATIONS Clarity of solution . . . . . . . . . . . . . . . . . . . . Passes test Visual transition interval . . . . . . . . . . . . . . . . From pH 6.8 (yellow) to pH 8.2 (red)
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4264 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
TESTS Clarity of Solution If the indicator is the sultone form, dissolve 0.1 g in 100 mL of ethyl alcohol. If the indicator is a salt form, dissolve 0.1 g in 100 mL of water. Not more than a faint trace of turbidity or insoluble matter should remain. Reserve the solution for the test for visual transition interval.
Visual Transition Interval Dissolve 1.0 g of potassium chloride in 100 mL of water. Adjust the pH of the solution to 6.8 (using a pH meter) with 0.01 N acid or alkali. Add 0.15 mL of the 0.1% solution reserved from the test for clarity of solution. The color of the solution should be yellow, with not more than a faint trace of green color. Titrate the solution with 0.01 N sodium hydroxide to a pH of 7.0 (using a pH meter). The color of the solution should be orange. Continue the titration to pH 8.2. The color of the solution should be red.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4264 ACS Reagent Chemicals, Part 4
