Question

Please write clearly, thanks!

Indigo is a deep blue dye. Why is the dye reduced to the colorless form to dye the fabric samples?

Answer 1

The oxidized form of Indigo is insoluble in water, but the reduced form is(water-soluble!). This is why Indigo is reduced to its colorless form by reducing agents so that it can be water-soluble because without making it dissolved in water, you cannot use it to dye clothes!

Meduction Na2S₂Oy [0] Indigo (Blue) Insoluble in water . Indigo coloylen Soluble in water

This makes the affinity of the indigo towards the fibers or cellulose much higher and the fibers become dyed by indigo. The dyed fibers are now exposed to air where the air oxidizes the indigo back to their insoluble blue-colored form and the fiber becomes colored by blue permanently.