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 0.520.
If a trial's absorbance is measured to be 0.275 and its initial concentration of SCN– was 0.00060 M, what is the equilibrium concentration of SCN–?
Use Beer's Law to determine the constant a in A = abc. You know concn, you know b, the cell length (but it is the same, I assume for both so actually you need not include that), and you know A. Calculate the constant a.
Then on the trial, you know A, you have found a, calculate concn, then use ICE to determine the equilibrium concn of SCN^-
Post your work if you need additional assistance.