Question

I am having trouble getting the right answer for this question please help.

Calculate Kc for the FeSCN2+ formation equilibrium
[FeSCN2+] = 3.49x10^-5 M
[Fe3+] = 4.39x10^-4 M
[SCN-] = 1.93x10^-4

Kc = [FeSCN2+] / ([Fe3+]-[FeSCN2+]) * ([SCN-] - [FeSCN2+])

I keep getting 546.266 M, but the answer is not right. It should be 412.
I am using the ICE method (initial, Change, Equilibrium).

Amanda

Answer 1

Where did you come up with the Kc expression? It should be
Kc = [FeSCN]^2+/(Fe^3+{)(SCN^-).
Kc = [3.49E-5]/[4.39E-4][1.93E-5]\ 411.9 which rounds to 412. :-)