In: Chemistry
Using your average Keq value (.3948), please calculate what the equilibrium concentrations of Fe3+ , SCN- , and FeSCN2+ in a solution made by combining 10.00mL of 0.0020M Fe(NO3)3 and 10.00mL of 0.0020M KSCN.
initial molarity of Fe+3 = 10 x 0.002 / 10 + 10 = 0.001 M
initial molarity of SCN- = 10 x 0.002 / 10 + 10 = 0.001 M
Fe+3 + SCN- ----------------------------------> FeSCN+2
0.001 0.001 0 -------------------------> initial
-x -x +x -----------------------------> changed
0.001-x 0.001-x x -------------------------> equilibrium
Keq = [FeSCN2+] [Fe+3] [SCN-]
0.3948 = x / (0.001-x)^2
0.3948 = x / x^2 + 10^-6 - 0.002 x
0.3948 x^2 - 0.999 x + 3.95 x 10^-7 = 0
x = 3.95 x 10^-7
equilibrium concentrations :
[Fe+3] = 0.001 - x = 9.996 x 10^-4 M
[SCN-] = 0.001 - x = 9.996 x 10^-4 M
[FeSCN+2] = x = 3.95 x 10^-7 M