1. A student mixes 5.00 mL 2.00 3 1023 M Fe(NO3)3 in 1 M HNO3
with 3.00 mL 2.00 3 1023 M KSCN and 2.00 mL of water. She finds
that in the equilibrium mixture the concentration of Fe(SCN)2+ is
7.0 3 1025 M. Find Kc for the reaction Fe3+(aq) + SCN-(aq)---->
Fe(SCN)2+(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 of FeSCN2+ are in the mixture at equilibrium?
What is the volume of the equi-
librium mixture? (Use Eq. 3.)
___________ mL; ___________ moles Fe(SCN)2+
How many moles of Fe3+ and SCN- are used up in making the
Fe(SCN)2+?
Step 3
How many moles of Fe3+ and SCN- remain in the solution
at equilibrium? (Use Eq. 4 and the results of Steps 1 and
2.)
___________ moles Fe3+; ___________ moles SCN-
Step 4
What are the concentrations of Fe3+, SCN- , and Fe(SCN)2+ at
equilibrium? (Use Eq. 3 and the results of Step 2 and Step 3.)
[Fe3+] 5 ___________ M; [SCN-] 5 ___________
M; [Fe(SCN)2+] 5 ___________ M
Step 5
What is the value of Kc for the reaction? (Use Eq. 2
and the results of Step 4.)
Kc= ___________