posted by Anonymous .
You want to measure the oxalic acid contents in 20 ml of a solution. To this end, you add 100 mmol sodium dichromate to the solution. Then you titrate the remainder of the dichromate with a Fe2+ solution of 1 mM, of which you need 11 ml. What was the concentration of oxalic acid in the original solution?
100 mmol Na2Cr2O7 initially. Some reacted with the oxalic acid, the excess is titrated with Fe^+2. 11 mL x 1 mM Fe^+2 = mmoles Fe^+2 titrant. Convert the Fe^+2 to mmoles Cr2O7^-2 using the coefficients in the balanced equation,then subtract mmoles Cr2O7^-2 from the 100 there initially. The difference is the amount of Cr2O7^-2 that reacted with the oxalic acid. Then convert mmoles Cr2O7^-2 that reacted to mmoles oxalic acid. The concn oxalic acid will be mmoles/20 mL.