Answer Happy

Select the max and determine the absorbance of each solution at this max. Using the absorbance of the 'known' solution together with the known concentration of FeSCN2+ determine the extinction coefficient for FeSCN2+.
0.30 M HNO3 stock solution. This solution will be used in the preparation of all solutions so as to avoid the hydrolysis of the Fe3+ solutions. 0.02 M KSCN stock solution (made up in 0.3 M HNO3). 0.20 M Fe(NO3)3 (made up in 0.3 M HNO3). Part A: Determination of max Prepare a 2.0 mM KSCN (2.0 x 10' M or 2.0 x 10-3 mol dm) solution (made up in 0.3 M HNO3) in a 50 cm volumetric flask. Place 5.0 cm of the 0.20 M Fe(NO3)3 and 2.0 cm of 2.0 mM KSCN solutions into a 10 cm volumetric flask. Make up to the mark with 0.3 M HNO3. In this mix the concentration of Fe(III) is very much greater than the concentration of thiocyanate and hence virtually all the added SCN is converted into the complex that is the concentration of FeSCN2+ is the same as SCN. (Note this solution serves as the 'known complex solution and will be used to convert the absorbance readings into concentrations using Equations 3). Measure the absorbance of this solution, using a UV spectrophotometer, between 350 and 600 nm and determine the wavelength of maximum absorption (Amax should be close to 450 nm).