Chapter 15, Problem 83P

Interpretation Introduction

Interpretation:

To predict the structure of the coloured compound when the given colourless compound come in contact with the acid treated sheet.

Concept introduction:

Acid-base indicators are the compounds which changetheir colour on changing the pH. The reaction of the acid-base indicator can be represented by:

In organic compounds chromophoreis the unsaturated part that imparts colour.  An auxochrome is a functional group attached to the chromophore which enhances its property.  The increased pi-conjugation decreases the energy gap between pi bonding and pi anti-bonding orbital.  The energy absorbs by the electron to get excited from pi bonding to pi anti-bonding orbital get decreased.  The wavelength of the emitted photon is in the visible region so the compound is intensely coloured.