Chemistry
posted by Anonymous .
The standard solution of FeSCN2+ (prepared by combining 9.00 mL of 0.200 M Fe(NO3)3 w/1.00 mL of 0.0020 M KSCN) has an absorbance of 0.530. If a trial's absorbance is measured to be 0.150 and its initial concentration of SCN– was 0.00070 M, the equilibrium concentration of SCN– will be ______
I saw your reply to this same problem, but with different concentrations, however I could not understand the steps to solving it

You have the standard. Calculate the concn of the complex. Then use Beer's Law to calculate the constant a, in A = abc.
You know A, you know b(the cell length) and you know c. Calculate the constant a. Then go to the unknown. You have A, you have a from the previous calculation, and you have b. Calculate c. That final c is the concn of the complex. You know what you started with; i.e., 0.00070 M, and you know the final c and you can calculate the difference.