5 Experiment Pre-lab 11.13.06 Reaction: Fe2+ reacts with 1,10 phenanthroline in this way: Fe2+ + 3 1,10 phenanthroline <=====> Fe(1,10 phenanthroline) 32+
Beer's law is as follows: A= bc A: measured absorbance : molar absorptivity constant M-1cm-1 b: path length or width of sample c: concentration of sample This states that the absorbance of a sample is equal to the molar absorptivity constant multiplied by the width of the sample and the concentration of the sample. Therefore, concentration and absorbance are directly proportional, and concentration and transmittance are inversely proportional. This means that if graphed, the concentration or absorbance can be determined from the calibration curve. Procedure: The Spec 20 will be turned on and allowed to warm up. Three samples of an unknown solution will be prepared using three tablets, tablet one per sample by boiling the tablet powder in a solution of water and HCl. Then a blank solution containing all of the ingredients but the Fe 2+ will be prepared for calibration between measurements. A stock solution of 5 g/mL Fe 2+ and 1,10 phenanthroline complex will be prepared from a more concentrated solution. The solutions will then be placed in the spectrometer and the absorbance of each solution will be calculated at each wavelength from the transmittance readouts. The unknown solution's three samples will be passed through the spectrometer to calculate the absorbance from the transmittance of those samples. The unknown absorbance will be determined from the calibration curve of the other samples, then determined using Beer's Law. This will allow the determination of the Fe2+ concentration in milligrams of the vitamin tablet.