Question

Why does nitric acid stain the skin yellow?

Answer 1

• The corrosive action of nitric acid (${\mathrm{HNO}}_3$) on the skin generates painful blisters.
• When it comes into contact with human skin, it combines with the protein (keratin) present in the human skin to generate xanthoproteic acid (${\mathrm{C}}_{34}{\mathrm{H}}_{24}{\mathrm{N}}_4{\mathrm{O}}_{12}2\mathrm{HO}$).
• Thus, nitric acid causes yellow stains and this reaction is known as xanthoproteic reaction.