Methyl orange

Methyl orange
Methyl orange
CAS number 547-58-0 YesY
ChemSpider 16736152 YesY
Jmol-3D images Image 1
Molecular formula C14H14N3NaO3S
Molar mass 327.33 g/mol
Density 1.28 g/cm3, solid
Melting point

>300 °C (Not precisely defined.)

Boiling point


Solubility in water Soluble in hot water
 YesY orange (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Methyl orange is a pH indicator frequently used in titrations.

It is often used in titrations because of its clear and distinct colour change. Because it changes colour at the pH of a mid-strength acid, it is usually used in titrations for acids. Unlike a universal indicator, methyl orange does not have a full spectrum of colour change, but has a sharper end point.

Methyl orange has mutagenic properties[1].


Indicator colours

Methyl orange (pH indicator)
below pH 3.1 above pH 4.4
3.1 4.4
Methyl orange in xylene cyanol solution (pH indicator)
below pH 3.2 above pH 4.2
3.2 4.2

In a solution becoming less acidic, methyl orange moves from red to orange and finally to yellow with the reverse occurring for a solution increasing in acidity. The entire colour change occurs in acidic conditions.

In an acid it is reddish and in alkali it is yellow. Methyl orange has a pKa of 3.47 in water at 25 degrees Celsius.[2]

Methyl orange

Other Indicators

  • Modified (or screened) methyl orange, an indicator consisting of a solution of methyl orange and xylene cyanol, changes from grey to green as the solution becomes more basic.
  • A number of other common indicators are tabulated in the article on pH indicators.

See also


  1. ^ MSDS from, Inc. Retrieved 2011-09-24
  2. ^ Sandberg, Richard G.; Henderson, Gary H.; White, Robert D.; Eyring, Edward M. (1972). "Kinetics of acid dissociation-ion recombination of aqueous methyl orange". The Journal of Physical Chemistry 76 (26): 4023–4025. doi:10.1021/j100670a024. 

External links

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Look at other dictionaries:

  • Methyl orange — Methyl Meth yl, n. [See {Methylene}.] (Chem.) A univalent hydrocarbon radical, {CH3 }, not existing alone but regarded as an essential residue of methane, and appearing as a component part of many derivatives; as, methyl alcohol, methyl ether,… …   The Collaborative International Dictionary of English

  • Méthyl orange — Hélianthine Pour les articles homonymes, voir MO. Hélianthine[1],[2 …   Wikipédia en Français

  • methyl orange — Helianthin He li*an thin, n. [Prob. fr. L. helianthes, or NL. helianthus, sunflower, in allusion to its color.] (Chem.) An artificial, orange dyestuff, analogous to tropaolin, and like it used as an indicator in alkalimetry; called also {methyl… …   The Collaborative International Dictionary of English

  • methyl orange — A weakly acid dye used as a pH indicator (red at 3.2, yellow at 4.4). SYN: helianthine. * * * methyl orange n a basic azo dye C14H14N3NaO3S that is used chiefly as an acid base indicator and whose dilute solution is yellow when neutral and pink… …   Medical dictionary

  • methyl orange — metiloranžinis statusas T sritis chemija apibrėžtis Indikatorius. formulė (CH₃)₂NC₆H₄N=NC₆H₄SO₃Na atitikmenys: angl. helianthin; methyl orange rus. гелиантин; метиловый оранжевый ryšiai: sinonimas – heliantinas sinonimas – natrio 4 [4… …   Chemijos terminų aiškinamasis žodynas

  • methyl orange — noun an azo dye used as an acid base indicator; used for titrations involving weak bases • Hypernyms: ↑azo dye, ↑acid base indicator * * * noun Usage: sometimes capitalized M&O : a basic azo dye (CH3)2NC6H4N . NC6H4SO3Na which is made by coupling …   Useful english dictionary

  • methyl orange — Chem. an orange yellow, slightly water soluble powder, C14H14N3NaO3S, used chiefly as an acid base indicator. Also called gold orange, helianthine B, orange III, tropaeolin D, tropeolin D. Cf. methyl red. [1880 85] * * * …   Universalium

  • methyl orange — meth′yl or′ange n. chem. an orange yellow, slightly water soluble powder, C14H14N3NaO3used chiefly as an acid base indicator • Etymology: 1880–85 …   From formal English to slang

  • methyl orange — noun Date: 1881 an alkaline dye used as a chemical indicator …   New Collegiate Dictionary

  • methyl orange — noun An azo dye used as an acid base indicator for titrations involving a weak base …   Wiktionary

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