Acid-base equilibria
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Could you please explain how are the methyl orange and methyl yellow different, and the reasons for the differences? 260308
Corrie writes .....
Methyl yellow is dimethylamino-azobenzene. I can't draw it here but it consists of two benzene rings joined by a -N=N- (azo) group. On one of the benzene rings is a dimethylamino group (-N(CH3 )2), opposite the azo group. The pH orange over which methyl yellow changes colour is 2.9 (red) - 4.0 (yellow).
Methyl orange has the same structure plus a sulphonic acid group on one of the benzene rings, opposite the azo- group. This converted into the sodium salt: -SO3Na. Being an ionic compound, this makes the indicator much more water soluble. Its pH range is also slightly different: 3.1 (red) - 4.4 (orange). Although it is more soluble, the colour change is not as obvious as that of methyl yellow.
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updated: 28 March 2008
