2 CrO4
2– + 2H
+ ® Cr2O7
2– + H2O
Cr2O7
2– + 2 OH
- ® 2 CrO4
2– + H2O
The 
structures 
of
chromate ion, CrO4
2– and
the dichromate ion, Cr2O7
2–
are shown below The
chromate ion is tetrahedral
whereas the dichromate ion
consists of two tetrahedra
sharing one corner with
Cr–O–Cr bond angle of 126° Sodium and potassium dichromates are strong oxidising agents;
the sodium salt has a greater solubility in water and is extensively
used as an oxidising agent in organic chemistry Potassium dichromate
is used as a primary standard in volumetric analysis