When a mixture of NaCl and K2Cr2O7 is heated with concentrated H2SO4, the dichromate ion oxidizes chloride ions. The reaction produces chromyl chloride (CrO2Cl), which is a volatile deep-red colored gas. The dichromate ion contains chromium in the +6 oxidation state. In the reaction, the dichromate is reduced and chloride is oxidized, but the chromium in the product remains in the +6 oxidation state as CrO2Cl (or as CrO2⁺ in ionic form). The gas evolved is CrO2Cl with chromium in the +6 oxidation state