Methyl orange
| Methyl orange | |
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4-dimethylaminoazobenzene-4'-sulfonic acid sodium salt |
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Other names
p-dimethylamino-azobenzenesulfonic acid |
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| Identifiers | |
| CAS number | 547-58-0  |
| ChemSpider | 16736152 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | C14H14N3NaO3S |
| Molar mass | 327.33 g/mol |
| Density | 1.28 g/cm3, solid |
| Melting point |
>300 °C (Not precisely defined.) |
| Boiling point |
Decomposes. |
| Solubility in water | Soluble in hot water |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| 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]
Contents |
[edit] 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]
[edit] 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.
[edit] See also
[edit] References
- ^ MSDS from ScienceLab.com, Inc. Retrieved 2011-09-24
- ^ 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.
