Final answer:
The color change during the reaction between o-vanillin and p-toluidine is due to the formation of a Schiff base, resulting in the creation of a double bond and generating a deeper color.
Step-by-step explanation:
The color change observed when o-vanillin reacts with p-toluidine is due to the formation of a Schiff base, which is a kind of imine. A Schiff base formation involves the reaction of an aldehyde group with an amine, resulting in the loss of water and the creation of a double bond, contributing to the color change.
This type of reaction generally leads to a deeper colored product, and the exact hue can vary depending on the specific compounds involved.
Indicators, such as phenolphthalein and methyl orange, showcase similar color changes when they transition between their acid and base forms.
The pH at which these indicators change color can be used to signal the end point of titration. Phenolphthalein, for example, changes from colorless to pink around its pKa value, which corresponds with the equivalence point in a titration curve.
Similar principles of color change are applied when using pH indicators like phenolphthalein, which transitions from colorless to pink at the equivalence point of a titration.