A 100 mL sample of water was treated to convert any iron present to `Fe^(2+)`. Addition of 25mL of 0.002M `K_(2)Cr_(2)O_(7)` resulted in the reaction.
`6Fe^(2+)+Cr_(2)O_(7)^(2-)+14H^(+) to 6Fe^(3+)+2Cr^(3+)+7H_(2)O`
The excess `K_(2)Cr_(2)O_(7)` was back- titrated with 7.5mL of .01M `Fe^(2+)` solution. Calculate the parts per million (ppm) of iron in the water sample.

Answer

126