Why is NAPHTHOL YELLOW S yellow in colour? How many hydrogen bonds occur in NAPHTHOL YELLOW S and why? If there is no hydrogen bonding then why? If there are hydrogen bonds then how many and why?

Expert Answers
ncchemist eNotes educator| Certified Educator

Naphthol Yellow S is a chemical dye.  It is based on a naphthyl group (two benzene rings fused together) as its central core.  It has two functional groups that could be involved in hydrogen bonding, a hydroxyl group (OH) and a sulfonic acid (SO3H).  But nathphol yellow s is a disodium salt.  That means that both of these functional groups have the hydrogen atoms replaced with sodium atoms.  Since both hydrogens are missing, this means that the chemical has no hydrogen bonds.  None of the other hydrogens in the compound are able to be used for hydrogen bonding.  As for why the chemical itself is colored yellow, that is because it absorbs all other wavelengths of visible light, but the yellow band of light is reflected, thus giving the appearance of yellow coloring.