Sulfur dioxide gas turns acidified potassium dichromate solution from orange to green reduced chromium +4 to +3.
K2Cr2O7 + 2H2SO4 + 3SO2 → 2Cr2(SO4)3 + K2SO4 + H2O
i)When the aqueous solution of potassium dichromate is treated with calculated amount of KOH, potassium chromate is formed.
K2Cr7O7 + 2KOH → 2K2CrO4 + H2O
ii) When an alkali is added to an orange red solution containing dichromate ions, a yellow solution is obtained due to the formation of chromate ions.
K2Cr2O7 + K2CO3 → 2 K2CrO4 + CO2