chemistry
posted by Gloria .
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 0.510. If a trial's absorbance is measured to be 0.250 and its initial concentration of SCN¡V was 0.00050 M, the equilibrium concentration of SCN¡V will be ?

Use Beer's Law and the standard to determine the constant a in A = abc. You know A, you know b, the cell length, and you can calculate c. Then turn your attention to the unknown and use A = abc.
You know A from the problem, a from the previous calculation, b the cell length, and solve for c, the concn of the unknown.If you know the initial concn of SCN^ and you know how much was used to form the FeSCN+2 complex, you can calculate the concn of SCN^ remaining at equilibrium.