Methyl orange
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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.
Names | |
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Preferred IUPAC name
Sodium 4-{[4-(dimethylamino)phenyl]diazenyl}benzene-1-sulfonate | |
Other names
Sodium 4-[(4-dimethylamino)phenylazo]benzenesulfonate | |
Identifiers | |
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3D model (JSmol) |
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ChemSpider |
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ECHA InfoCard | 100.008.115 |
EC Number |
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PubChem CID |
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UNII | |
UN number | 3143 |
CompTox Dashboard (EPA) |
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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: | |
Danger | |
H301 | |
P308, P310 | |
NFPA 704 (fire diamond) | |
Lethal dose or concentration (LD, LC): | |
LD50 (median dose) |
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).
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