Titration question

Question

 An 0.0151 L acidic solution of potassium dichromate is titrated with a solution of 0.125 mol/L iron (II) chloride. The concentration of potassium dichromate according to the experimental evidence shown for the amount of iron (II) chloride used is a.bcde mol/L

1. Input your value for a.bcde in the blank
2. Include the decimal 
3. Do not include units

I	II	III
Final Buret Reading (mL)	12.6	26.8	38.7
Initial Buret Reading (mL)	0.400	12.7	26.5
Color at Endpoint	Light Pink	Bright Pink	Light Pink

Answer 1

Do the calculation for each column and average the concentrations of K dichromate. Note that the middle column was an overshoot and you could make a case for omitting it in the average.

You need the stoichiometry for the redox reaction:

Fe²⁺ --> Fe³⁺ + e^-

Cr₂O₇^2- + 6 e^- +14H⁺ --> 2Cr³⁺ + 7H₂O

You can work out the overall reaction. What matters is that 1 dichromate ion requires 6 Fe²⁺

If you use stoichiometry to find molarity, you should find the moles and then divide by the amount of fluid you started with.

Column 1 :

(12.6 ml - .4 ml) (1 liter/1000 ml)(.0151 moles FeCl₂/liter of soln)(1Fe²⁺/FeCl₂)(1 Dichromate/6 Fe²⁺)(1 Pot. Dichromate/1 Dichromate) = moles of potassium dichromate

To find the molarity divide the moles by the starting volume(in liters) of the dichromate soln which is not given.

Please consider a tutor.