Hydrogen peroxide acts as an oxidising as well as a reducing agent in both acidic and alkaline media.

When ${\mathrm{H}}_2{\mathrm{O}}_2$ is added to an acidified potassium dichromate solution, the blue coloured compound ${\mathrm{CrO}}_5$ or $\mathrm{CrO}({\mathrm{O}}_2{)}_2$  is formed. The chemical reaction is as follows

${\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}+2{\mathrm{H}}^{+}+4{\mathrm{H}}_2{\mathrm{O}}_2\to 2\mathrm{CrO}{\left({\mathrm{O}}_2\right)}_2$$+$$5 {\mathrm{H}}_2\mathrm{O}$