Potassium dichromate is used as'lab reagent and dichromate ion can be used as a primary standard in volumetric analysis.(1)/(2)Cr_(2)O_(7)^(2-)+7H^(+)+3e^(-)iffCr^(3+)+3(1)/(2)H_(2)O,E^(@)=1.33V WhenH_(2)O_(2) is added to an acidified' solution of dichromate, a complicated reaction occurs. The formation of product depends on the pH value and concentration of dichromate ions. A deep-blue violet peroxo compound X is formed which decomposes rapidly in aqueous solution. This compound can be extracted in ether, where it reacts with pyridine forming the adduct PyCro(O_(2))_(2) In alkaline solution, K_(2)Cr_(2)O_(7) with 30% H_(2)O_(2) a red-brown compound Y (K_(3) CrO_(8) is formed. In ammonia solution the dark red-brown compound. Z [(NH_(3)),CrO_(4)] is formed. In alkaline solution, dichromate ion changes to chromate ion which is also used as reagent in quantitative analysis of cationsQThe shape of compound (Z) is