Methyl orange

Methyl Orange is a pH indicator frequently used in titrations. It is also toxic.

It is often chosen to be used in titrations because of its clear colour change. Unlike universal indicator, methyl orange doesn't have a full spectrum of colour change, but has a sharper end point.

Indicator Colours

Methyl Orange moves from red through orange and to yellow, or from yellow through orange to red. This is not ideal for titration but in many cases it is still used as its colour change is normally clear enough. On ocassions, however, it can be very difficult to notice the exact time of arrival at red or yellow because the difference isn't very stark.

Acidic Conditions Red

↔

End-Point of Titration Orange

↔

Basic Conditions Yellow

The table above summarises this information on colour change,

Chemical Information

Methyl orange solid is more specifically:

Sodium p-Dimethylaminoazobenzenesulfonate

C₁₄H₁₄N₃O₃SNa

4-NaOSO₂C₆H₄N:NC₆H₄-4-N(CH₃)₂

Its formula weight is approximatly 327.34 grams per mole.

Other Indicators

• Phenolphthalein is another indicator frequently used in acid-base titration reactions because of its very sharp color change.
• A number of other common indicators are tabulated in the article on pH indicators.

External links

• Informative page on different titration indicators, including Methyl Orange