Question

Calculate the pre-equilibrium concentration of Fe3+(aq) in a solution made by mixing 1.7 mL of 2.0 ✕ 10−3 M Fe(NO3)3 and 8.3 mL of 2.0 ✕ 10−3 M NaSCN. Assume the final volume is 10.0 mL.

i wasnt suere on whether i should compose an ice table for this problem? An explaination of this problem through a solution would be helpful.

Answer 1

The term pre-equilibrium concentration is not very clear to me. You can calculate the exact concentration of any reactant at any point of the reaction from the knowledge of the kinetics of the reaction. I think here you are supposed to calculate simply the concentration of Fe³⁺ in the reaction mixture before the reaction starts, i.e., at t =0. For that you don't need an ICE chart.

You have used 1.7 mL of 2.0 ✕ 10⁻³ M Fe(NO₃)₃ and total volume after mixing is 10 mL .

Use the equation to calculate the final concentration: V₁S₁ = V₂S₂

where , V₁ = initial volume = 1.7 mL

S₁ = initial concentration before mixing = 2.0 ✕ 10⁻³ M

V₂ = final volume = 10 mL

S₂ = concentration after mixing (before the reaction starts)

So, S₂ = V₁S₁ / V₂ = [(1.7 mL) *( 2.0 ✕ 10⁻³ M)] / 10 mL

= 3.4*10^-4 M