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– was 0.00050 M, the equilibrium concentration of SCN– will be

Question

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–  was 0.00050 M, the equilibrium concentration of SCN–  will be

what formulas are there that relate absorbance and concentration ?

DrBob222 · Answer

Use Beer's Law, A=abc for the standard to determine the constant, a. Then use A=abc on the unknown to determine c and use that and ICE to arrive at the amount of SCN^- at equilibrium.