Question

You wish to measure the iron content of the well water on the new property you are about to buy. You prepare a reference standard Fe3+ solution with a concentration of 7.10 x 10-4 M. You treat 15.0 mL of this reference with HNO3 and excess KSCN to form a red complex and dilute the reference to 50.0 mL. The diluted reference is placed in a cell with a 1.00-cm light path. You then take 25.0 mL of the well water, treat with HNO3 and excess KSCN, and dilute to 100.0 mL. This diluted sample is placed in a variable pathlength cell. The absorbance of the reference and the sample solutions match when the pathlength is 1.54 cm. What is the concentration of iron in the well water? For each solution, the zero is set with a blank. [Fe3+]well water = = Jwell water

Answer 1

The law used is Lambert-Beers law, which states that the light absorbed by a solution is directly proportional to the path length and the concentration of the solution. This law holds for extremely dilute solutions, for concentrated solutions, the absorbance vs concentration graph will show a non linear relation.

Reference solution: concentration of det say a= 7.10x10 cm) when diluted. Cfe+3), G 9x15 = 2.13 x10 h (M) from Lambert-Beers bowo, A= e.ge od= Lem » A=&C. - Well heater ! let the Pre +3] be co. After diluiting, cz= cх 25o = 10 coith a call length = 1.54cm, the absorbances are some e.cz = E C3 ar c= 42 C2 = ux 2.13x10" (m) concentration of [Fe ] is well water = 8.52x10 " (M) = 0.852 mm.