Question

Equilibria can be treated mathematically with the equilibrium constant, K. For the reaction Fe3+ + SCN − equilibrium reaction arrow FeSCN2+, the equilibrium constant expression is [FeSCN2+ ] K = [Fe3+ ] · [SCN − ] where, for example, [Fe3+ ] is the molar concentration (mol Fe3+ / L solution) present in an equilibrium mixture. At some temperature, a chemist found the following equilibrium concentrations. [Fe3+ ] = 8.17 ✕ 10−3 M, [SCN − ] = 8.60 ✕ 10−3 M, [FeSCN2+ ] = 6.25 ✕ 10−2 M

What is value of K?

Suppose that some FeSCN²⁺ is added to the above solution to shift the equilibrium. When equilibrium is re-established, the following concentrations are found.

[Fe³⁺ ] = 8.34 ✕ 10⁻³M,     [SCN⁻ ] = 8.77 ✕ 10⁻³M

What is the concentration of FeSCN²⁺ in the new equilibrium mixture? Hint: Use your value of K to solve for the unknown concentration.

Answer 1

Gwin FeseN Re 3+ + 2t ] SEN (I) Fe3+ [sCN K ea 14 [Resen 2] -3 8.17 X10x 8.6X10-3 Ker 6. 25 X 10-2 Kea 11.24 X 10 (II) Crest CseN [FescN 2 1 kea -3 8-34 X 10 1.24 X 10 TresoN ] -2 Cfe sCN 6.5 X 10