[boston003]

A solution in part B is prepared by combining 2.02 mL 0.00401 molar SCN-, 8.00 mL of 0.00402 molar Fe3+, 4.99 mL of 1.0 molar HNO3, and 5.00 mL water. Based on this information, the initial concentration of SCN- is? The initial concentration of Fe2+ is?

[Babcock_Hall]

One, it is a forum rule that you must show your attempt before we can help you.  Two, are you sure that you have copied the problem correctly?  You mention both Fe³⁺ and Fe²⁺.

[boston003]

Yes, I think the problem was mistyped, it is suppose to be Fe3+. I used the dilution formula M1V1=M2V2. For SCN- I got 0.00401(2.02)= M2 (20.02) and ended up with 0.000404 M. For Fe3+, 0.00402 (8.00)= M2 (20.01) and got M2=0.00160 M. This problem wants correct sig figs as well, this is online homwork and I got these wrong the first time i submitted it, not sure what I did wrong.

[Babcock_Hall]

Looks like you put the wrong volume into your formula.  Dilution calculations are interesting in that it is necessary, but not sufficient, to make sure that units cancel in the usual way.