Question

Consider the following reaction:
Fe3+(aq)+SCN−(aq)⇌FeSCN2+(aq)
A solution is made containing an initial [Fe3+] of 1.1×10⁻³ M and an initial [SCN−] of 8.2×10⁻⁴ M. At equilibrium, [FeSCN2+]= 1.8×10⁻⁴ M .

Part A

Calculate the value of the equilibrium constant (Kc).

Express your answer using two significant figures.

Kc=

Answer 1

                           Fe3+(aq)             +                SCN−(aq)⇌                          FeSCN2+(aq)

Initial                 1.1×10⁻³                                8.2×10⁻⁴                                                        0

Change             -1.8×10⁻⁴    -1.8×10⁻⁴    +1.8×10⁻⁴

At equilibrium    1.1×10⁻³ - 1.8×10−4                 8.2×10−4 - 1.8×10−4                   1.8×10⁻⁴   

Hence Kc = [FeSCN2+] / [Fe3+] [SCN−].

               =   [1.8×10−4] / [0.00092] [0.00064]

              Kc = 305.706