Methyl orange
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
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 pHa of 3.47 in water at 25 °C (77 °F).
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.
Safety
Methyl orange has mutagenic properties. Direct contact should be avoided.
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