Methyl orange
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| Names | |
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| IUPAC name
4-dimethylaminoazobenzene-4'-sulfonic acid sodium salt
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| Other names
p-dimethylamino-azobenzenesulfonic acid
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| Identifiers | |
3D model (JSmol)
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| ECHA InfoCard | 100.008.115 |
CompTox Dashboard (EPA)
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| Properties | |
| C14H14N3NaO3S | |
| Molar mass | 327.33 g/mol |
| Density | 1.28 g/cm3, solid |
| Melting point | >300 °C (Not precisely defined.) |
| Boiling point | Decomposes. |
| Soluble in hot water | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Methyl orange is a pH indicator frequently used in titrations.
It is often chosen to be used in titrations because of its clear 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.
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. It should be noted that the entire colour change occurs in acidic conditions.
In an acid it is reddish and in alkali it is yellow.
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.