Methyl orange

Methyl orange
Names



IUPAC name Sodium 4-[(4-dimethylamino)phenyldiazenyl]benzenesulfonate
Other names Sodium 4-[(4-dimethylamino)phenylazo]benzenesulfonate
Identifiers
CAS Number	547-58-0^Y
ChemSpider	16736152^Y
Jmol 3D model	Interactive image
InChI InChI=1S/C14H15N3O3S.Na/c1-17(2)13-7-3-11(4-8-13)15-16-12-5-9-14(10-6-12)21(18,19)20;/h3-10H,1-2H3,(H,18,19,20);/q;+1/p-1^Y Key: STZCRXQWRGQSJD-UHFFFAOYSA-M^Y InChI=1/C14H15N3O3S.Na/c1-17(2)13-7-3-11(4-8-13)15-16-12-5-9-14(10-6-12)21(18,19)20;/h3-10H,1-2H3,(H,18,19,20);/q;+1/p-1 Key: STZCRXQWRGQSJD-REWHXWOFAG
SMILES [Na+].CN(C)c2ccc(/N=N/c1ccc(cc1)S([O-])(=O)=O)cc2
Properties
Chemical formula	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
Solubility in water	0.5 g/100 mL (20 °C)
Solubility	insoluble in diethyl ether^[1]
Hazards
Main hazards	Toxic (T)
GHS pictograms
GHS signal word	Danger
GHS hazard statements	H301
GHS precautionary statements	P308, P310
EU classification (DSD)	T
R-phrases	R25
S-phrases	S37, S45
NFPA 704	^[1] 0 1 0
Lethal dose or concentration (LD, LC):
LD₅₀ (Median dose)	60 mg/kg (rat, oral)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y verify (what is ^YN ?)
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. Methyl orange shows orange colour in acidic medium and yellow colour in basic medium.

Indicator colours

Methyl orange solutions

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 pH_a of 3.47 in water at 25 °C (77 °F).^[2]

Other indicators

Main article: pH indicator

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.

References

1 2 3 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.

External links

Wikimedia Commons has media related to Methyl orange.

Informative page on different titration indicators, including Methyl Orange

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