Methyl Red Indicator ACS, Ph Eur C.I. 13020


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C.I. 13020  (Acid Red 2)

Methyl red (2-(N,N-Dimethyl-4-aminophenyl)azobenzenecarboxylic acid), also called C.I. Acid Red 2, is an indicator dye that turns red in acidic solutions. It is an azo dye, and is a dark red crystalline powder. Methyl red is a pH indicator; it is red in pH under 4.4, yellow in pH over 6.2, and orange in between, with a pKa of 5.1.

  • pH Indicator
  • Identification of bacteria in Microbiology

C.I. 13020

Molecular Formula: C15H15N3O2 
Molecular Weight: 269.30
Melting Point: 179-182°C
Absorbtion Min (pH 4.5 Buffer): 523-526nm
Absorbtion Max (pH 4.5 Buffer): 427-437nm
Specific Absorbitvity (A1%/1cm): 1350-1450 (0.005g/L Buffer pH 4.5)
Specific Absorbitvity (A1%/1cm): 700-800 (0.005g/L Buffer pH 6.2)
Transition Range: pH 4.4-6.0 (Red-Yellow)
Loss on Drying (110degC): <5%

Hazard Phrases: Toxic to aquatic life with long lasting effects.

Prec Phrases: Avoid release to the environment. Collect spillage. Dispose of contents/container.

Cas No: 493-52-7
Einecs No: 207-776-1


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