A student mixes 5.00 mL 2.00 X 10~3 M Fe(NO3)3 with 5.00 mL 2.00 X 10-3 M KSCN. She finds that in the equilibrium mixture the concentration of FeSCN2+ is 1.40 X 10-4 M. Find Kc for the reaction Fe3+(aq) + SCN-(aq) (arrows) FeSCN2 (aq).
Step 1. Find the number of moles Fe3+ and SCN- initially present. (Use Eq. 3.)
moles Fe3+; moles SCN-
Step 2. How many moles FeSCN2+ are in the mixture at equilibrium? What is the volume of the equilibrium mixture? (Use Eq. 3.)
.
mL; moles FeSCN2+
How many moles of Fe3+ and SCN~ are used up in making the FeSCN2"1"?
.
moles Fe3+; moles SCN-
Step 3. How many moles of Fe3+ and SCN- remain hi the solution at equilibrium? (Use Eq. 4 and the results of Steps 1 and 2.)
molesFe3+ molesSCN-
Step 4. What are the concentrations of Fe3*, SCN-, and FeSCN2+ at equilibrium? What is the volume of the equilibrium mixture? (Use Eq. 3 and the results of Step 3.)

[Fe3+] = M; [SCN-] = M; [FeSCN2*] = M
mL
Step 5. What is the value of Kc for the reaction? (Use Eq. 2 and the results of Step 4.)
Kc=