$2{\mathrm{Na}}_2{\mathrm{CrO}}_4+{\mathrm{H}}_2{\mathrm{SO}}_4\to {\mathrm{Na}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7+{\mathrm{Na}}_2{\mathrm{SO}}_4+{\mathrm{H}}_2\mathrm{O}$

${\mathrm{CrO}}_4^{ 2-}$(chromate ion) has a yellow tint. When H⁺ oxidizes ${\mathrm{Cr}}_2{\mathrm{O}}_7^{ 2-}$ (dichromate ion), the hue changes to orange.

Sulfuric acid, also known as sulphuric acid or oil of vitriol, is a mineral acid made up of the elements hydrogen, oxygen, and sulphur. It is a viscous liquid that is miscible with water. It has no colour or smell.