 We have prepared a series of solutions of known concentrations of the complex ion. We will use a spectrophotometer to read the absorbance of those solutions. We will make a Beer's Law plot of absorbance versus concentration to make a calibration line. We set the wavelength on the Spectronic 20 to 447 nanometers. At this wavelength, the complex ion absorbs strongly, but the thiocyanate ion and the iron plus 3 ion do not. We set the 0% T with nothing in the cell holder. Our blank contains 0.1 molar nitric acid. We set the 100% T with the nitric acid solution. We will then measure the % T of each of the solutions and calculate the absorbance from the % T. After you have read the % T of the standard solutions, you will prepare equilibrium mixtures of iron plus 3 and thiocyanate by pouring the iron plus 3 solution and the thiocyanate solution to a beaker. Swirl them so they mix and transfer your solution to the cuvette. You will then read the % transmittance of each of the equilibrium mixtures that you have prepared.