If 42 mL of Cr2O7-2(aq) solution is titrated to the endpoint with 172 mL of 0.15 M Cl-, what was the concentation of Cr2O7-2 solution?

Question

I got the reaction
14 H+(aq) _ Cr2O7-2(aq) + 6 Cl- = 2 Cr+3(aq) + 3 Cl2(g) + 7 H20(l)

Now I have drawn a blank. Please help!

Answer 1

mols Cl^- = M x L = ?
Using the coefficients in the balanced equation, convert mols Cl^- to mols Cr2O7^2-. That's mols Cl^ x (1 mol Cr2O6/5 mols Cl^-) = ?
Then M Cr2O7 = mols/L