In an acidified dichromate solution, a pinch of Na₂O₂ is added and shaken. What is observed?

The acidified potassium dichromate solution becomes the rich blue ${\mathrm{CrO}}_5$ when ${\mathrm{Na}}_2{\mathrm{O}}_2$ is added.

${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7+{\mathrm{H}}_2{\mathrm{SO}}_4+4{\mathrm{Na}}_2{\mathrm{O}}_2\to 2{\mathrm{CrO}}_5+{\mathrm{K}}_2{\mathrm{SO}}_4+{\mathrm{H}}_2\mathrm{O}+4{\mathrm{Na}}_2{\mathrm{O}}_2$
 

The production of chromic sulphate causes the intense blue colour to fade. Through this process, oxygen is created.

$4{\mathrm{CrO}}_5+6{\mathrm{H}}_2{\mathrm{SO}}_4\to 2{\mathrm{Cr}}_2{\left({\mathrm{SO}}_4\right)}_3+6{\mathrm{H}}_2\mathrm{O}+7{\mathrm{O}}_2$