Methyl orange
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Names | |
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IUPAC name
Sodium 4-[(4-dimethylamino)phenyldiazenyl]benzenesulfonate
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Other names
Sodium 4-[(4-dimethylamino)phenylazo]benzenesulfonate
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Identifiers | |
547-58-0 ![]() |
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ChemSpider | 16736152 ![]() |
Jmol 3D model | Interactive image |
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Properties | |
C14H14N3NaO3S | |
Molar mass | 327.33 g·mol−1 |
Density | 1.28 g/cm3, solid |
Melting point | >300 °C (572 °F; 573 K) not precisely defined |
Boiling point | decomposes |
0.5 g/100 mL (20 °C) soluble in hot water |
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Solubility | insoluble in diethyl ether[1] |
Vapor pressure | {{{value}}} |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references | |
Methyl orange is a pH indicator frequently used in titrations because of its clear and distinct colour change. Because it changes colour at the pH of a midstrength 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
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.
Methyl orange (pH indicator) | ||
below pH 3.1 | above pH 4.4 | |
3.1 | ⇌ | 4.4 |
In an acid, it is reddish and in alkali, it is yellow. Methyl orange has a pHa of 3.47 in water at 25 °C (77 °F).[2]
Other indicators
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Methyl orange in xylene cyanol solution (pH indicator) | ||
below pH 3.2 | above pH 4.2 | |
3.2 | ⇌ | 4.2 |
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.
Safety
Methyl orange has mutagenic properties.[1] Direct contact should be avoided.
See also
References
External links
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Wikimedia Commons has media related to Methyl orange. |