Methyl orange

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Methyl orange



IUPAC name	4-dimethylaminoazobenzene-4'-sulfonic acid sodium salt
Other names	p-dimethylamino-azobenzenesulfonic acid
Identifiers
CAS number	[547-58-0]
SMILES	CN(C)c1ccc(cc1)N=Nc2ccc(cc2)S(=O)(=O)O[Na]
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
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

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.

[edit] Indicator colours

Methyl orange (pH indicator)
below pH 3.1		above pH 4.4
3.1	↔	4.4

Methyl orange in xylene cyanole 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.

[edit] Other Indicators

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