Question

In: Chemistry

Using your average Keq value (.3948), please calculate what the equilibrium concentrations of Fe3+ , SCN-...

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.

Solutions

Expert Solution

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


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