Please Help!! I have no idea where to start with this one! A 100.0mL sample of water was treated to convert any iron present to ferrous ion. Addition of 25mL of 0.002107M potassium dichromate converted the iron to ferric ion and the dichromate to Cr3+. Excess dichromate was then back titrated with 7.47 mL of standard 0.00979M Fe2+. Calculate the ppm iron in the original solution.