K_2Cr_2O_7 acts as a good oxidizing agent in acidic mediumunderset("Orange")(Cr_(2)O_(7)^(2-)) + 14H^(+) + 6e^(-) rarr underset("Green")(2Cr^(3+)) + 7H_2O In alkaline solution, orange colour of Cr_(2)O_(7)^(2-) chages to yellow colour due to formation of Cr_2O_(4)^(2-) and again yellow colour changes to orange colour on changing the solution to acidic medium underset("Orange")(Cr_2O_7^(2-))+2OH^(_) rarrunderset("Yellow")(Cr_2O_7^(2-))+H_2O underset("Yellow")(2CrO_(4)^(2_-)) + 2H^(+) rarr underset("Orange")(Cr_(2)O_(7)^(2-) + H_(2)O) Cr_(4)^(2-) and Cr_(2)O_(7)^(2-) exist in equilibrium at pH =4 and are interconvertible by altering the pH of the solution. When heated with H_2SO_4 and metal chloride K_2Cr_2O_7 gives vapour of chromyl chloride (CrO_2Cl_2) . Chromyl chloride (CrO_2Cl_2)when passed into aqueous NaOH solution, yellow colour solution of CrO_(4)^(2-)is obtained. This on reaction with lead acetate gives yellow ppt. PbCrO_4 . When H_2O_2 is added to an acidified solution of dichromate ion, a complicated reaction occurs. The products obtained depend on the pH and concentration of dichromate. Cr_2O_7^(2-)+2H^(+) + 4H_(2)O_(2) rarr 2Cr(O_2)+5H_2O A deep blue-violet coloured peroxo compound, CrO(O_2)_2,' called chromic peroxide is formed. This decomposes rapidly in aqueous solution into Cr^(3+)and xygen. CrO_3 on reaction with HCl and the product on reaction with NaOH(aq) give respectively