In analytical chemistry, solutions of potassium dichromate, K2Cr2O7 (a powerful oxidizing agent), are used to determine the amount of iron present in samples. This analysis is carried out by reacting iron(II) with an acidic solution containing Cr2O72−. During the reaction, the orange dichromate ion forms green Cr3+ ion and iron(II) ion is oxidized to iron(III) ion. What is the overall ionic equation for this reaction? Including the phases is optional. Express your answer as a chemical equation.