Methyl orange

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Methyl orange
Methyl orange sample solution.jpg
Methyl orange in solid form and as solution at pH < 3.1 (red), pH 3.1-4.4 (orange) and pH > 4.4 (yellow)
Preferred IUPAC name
Sodium 4-{[4-(dimethylamino)phenyl] diazenyl} benzene-1-sulfonate
Other names
C.I. Acid Orange 52
Eniamethyl Orange
Gold Orange
Orange III
Sodium 4-[(4-dimethylamino)phenylazo]benzenesulfonate
Molar mass 327.33 g/mol
Density 1.28 g/cm3
Melting point 300 °C (572 °F; 573 K) (decomposes)
Boiling point Decomposes
0.5 g/100 ml (20 °C)
Solubility Slightly soluble in ethanol
Insoluble in butanol, diethyl ether, glycerol, isobutanol, toluene, xylene
Solubility in 2-methoxyethanol 2 g/100 ml
Solubility in ethanol 0.03 g/100 ml
Safety data sheet Sigma-Aldrich
Lethal dose or concentration (LD, LC):
60 mg/kg (rat, oral)
Related compounds
Related compounds
Methyl red
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Methyl orange is an organic chemical compound used as pH indicator in titrations. Because it changes colour at the pH of a midstrength acid, it is usually used in titrations for acids.



Methyl orange turns red in strong acidic solutions and yellow at high pH. In the presence of xylene cyanol, it turns acidic solutions mauve and alkaline green.


Methyl orange is a light orange powder, slightly soluble in water and ethanol, but more soluble in pyrimidine.


Methyl orange can be bought from chemical suppliers or online, from eBay or Amazon.


Ozonelabs wrote a synthesis of methyl orange. It can be downloaded here.

Methyl orange is cheaper to purchase than synthesize yourself.


  • pH indicator



Methyl orange will stain most objects. It is also toxic if ingested. Studies have shown to be mutagen. Proper protection should be worn when handling the compound.


In closed bottles, away from acids and volatile compounds.


Methyl orange should be destroyed with a strong oxidizer, such as piranha solution, Fenton's reagent or chromic acid. This neutralizes it to carbon dioxide, water and salt. Excess oxidizer is then neutralized and checked for any leftover methyl orange; the leftover solution can then be safely poured down the drain.


Relevant Sciencemadness threads