Video: The chromate-dichromate equilibrium I
The yellow chromate ion and orange dichromate ion are in equilibrium, with the chromate ion predominating in base and the dichromate ion in acid. Addition of hydrogen (hydronium) ion to chromate ion solution will drive the equilibrium towards dichromate:2 CrO42-(aq) + 2 H+(aq) ® Cr2O72-(aq) + H2O(l)
Addition of hydroxide ion to dichromate ion solution will drive the equilibrium towards chromate:
Cr2O72-(aq) + 2 OH-(aq) ® 2 CrO42-(aq) + H2O(l)