Question

A reaction mixture is formed by mixing 2.0 mL of 0.010 M Fe3+ and 2.0 mL of 0.010 M SCN–, and the diluting the solution to a total volume of 25.0 mL. Calculate the initial concentrations of Fe3+ and SCN– under these conditions.

Some experiments have indicated that this reaction has an equilibrium constant, Kf , of approximately 300. Use the value of Kf = 300 to calculate the equilibrium concentrations of all three species given the initial concentrations from problem 1.

Answer 1

Molarity of Fe³⁺ = 0.010 M

Volume taken = 2 mL i.e. 0.002 L

So, moles added = 0.01 M x 0.002 L = 0.00002 moles

Total volume of mixture = 25 mL i.e. 0.025 L

Final molarity of Fe³⁺ = 0.00002 moles/0.025 L = 0.0008 M

Similarly, final molarity of SCN^- = 0.0008 M