Application of Spectroscopy:You wish to measure the iron content of the well water on thenew property you are about to buy. You prepare a referencestandard Fe3+ solution with a concentration of 7.50 x 10-4 M. Youtreat 15.0 mL of this reference with HNO, and excess KSCN toform a red complex, and dilute the reference to 55.0 mL. Thediluted reference is placed in a cell with a 1.00-cm light path. Youthen take 15.0 mL of the well water, treat with HNO, and excessKSCN, and dilute to 100.0 mL. This diluted sample is placed in avariable pathlength cell. The absorbance of the reference and thesample solutions match when the pathlength is 1.91 cm.What is the concentration of iron in the well water?For each solution, the zero is set with a blank.

Absorbance is directly proportional to the concentration of the colored sample as per Lambert-beer's Law. A=εcl Where, A = Absorbance, c = concentration, l = path length, ε = Molar extinction coefficient. Given, Path length of diluted reference = 1cm. Path length of sample solution = 1.91cm.For reference solution: M1V1 = M2V2 (7.50×10-4M)×15.0ml=M2×55.0mlM2 = 2.045×10-4M For sample solution: Absorbance of both the solution is equal, thus Absorbance of reference solution = Absorbance of sample solution ε×(2.045×10-4M)×1.00cm = ε×cdiluted×1.91cmcdiluted = 1.070×10-4M Now, the initial concentration of the sample before dilution will be: cdiluted = 1.070×10-4MInitial volume×Final volumecdiluted = 1.070×10-4M15.0ml×100.0mlcdiluted = 7.133×10-4M