Methyl orange

Methyl orange
Names
Preferred IUPAC name
Sodium 4-{[4-(dimethylamino)phenyl]diazenyl}benzene-1-sulfonate
Other names
Sodium 4-[(4-dimethylamino)phenylazo]benzenesulfonate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.008.115 Edit this at Wikidata
EC Number
  • 208-925-3
UNII
UN number 3143
  • InChI=1S/C14H15N3O3S.Na/c1-17(2)13-7-3-11(4-8-13)15-16-12-5-9-14(10-6-12)21(18,19)20;/h3-10H,1-2H3,(H,18,19,20);/q;+1/p-1 checkY
    Key: STZCRXQWRGQSJD-UHFFFAOYSA-M checkY
  • InChI=1/C14H15N3O3S.Na/c1-17(2)13-7-3-11(4-8-13)15-16-12-5-9-14(10-6-12)21(18,19)20;/h3-10H,1-2H3,(H,18,19,20);/q;+1/p-1
    Key: STZCRXQWRGQSJD-REWHXWOFAG
  • [Na+].CN(C)c2ccc(/N=N/c1ccc(cc1)S([O-])(=O)=O)cc2
Properties
C14H14N3NaO3S
Molar mass 327.33 g·mol−1
Appearance Orange or yellow solid[1]
Density 1.28 g/cm3
Melting point > 300 °C (572 °F; 573 K) (not precisely defined)
Boiling point Decomposes[1]
5 g/L (20 °C)
Solubility in diethyl ether Insoluble[2]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Toxic (T)
GHS labelling:
GHS06: Toxic
Danger
H301
P308, P310
NFPA 704 (fire diamond)
[2]
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
0
0
Lethal dose or concentration (LD, LC):
60 mg/kg (rat, oral)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Methyl orange is a pH indicator frequently used in titration because of its clear and distinct color variance at different pH values. Methyl orange shows red color in acidic medium and yellow color in basic medium. Because it changes color at the pKa of a mid strength acid, it is usually used in titration of strong acids in weak bases that reach the equivalence point at a pH of 3.1-4.4.[3] Unlike a universal indicator, methyl orange does not have a full spectrum of color change, but it has a sharp end point. In a solution becoming less acidic, methyl orange changes from red to orange and, finally, to yellow—with the reverse process occurring in a solution of increasing acidity.

  1. ^ a b Haynes, William M., ed. (2016). CRC Handbook of Chemistry and Physics (97th ed.). CRC Press. p. 3.384. ISBN 9781498754293.
  2. ^ a b Cite error: The named reference sciencelab was invoked but never defined (see the help page).
  3. ^ Clark, J. "Acid Base Indicators". ChemGuide. Retrieved November 12, 2022.