Molarity Of Phenanthroline

To construct a calibration curve, three samples with different known concentrations and a blank solution are prepared and their absorbances are measured with a UV-Vis spectrophotometer (Table 1). The absorbances of three unknown samples with same concentration and a blank are measured (Table 2). The blank solutions are used as a reference solution to calibrate the colorimeter. The volumes of Fe solution for the delivery volume errors in the 10 ml graduated pipet are corrected (Table 3). The molarity (μg/mL) of Fe (o-phenanthroline)32+ in each standard solution is calculated by equation 2 (Table 4). A graph of absorbance versus μg/ml of Fe in the five calibration standards is plotted (Figure 1). The molarity (mol/L) of Fe (o-phenanthroline)32+ in each standard solution is calculated by equation 3.
The average molar absorptivity is 1.14 x 103 M-1cm-1 (equation 5). The average of the three absorbance values for the unknown is 0.251 (equation 6). The standard deviation is 0.0222 (equation 7). Using the Beer’s Law plot and the average absorbance value, the concentration of the Fe solution after dilution is 1.29 µg/ mL (equation 8). The concentration of Fe solution before dilution is 0.000108 mol/L (equation 9). The mass of Fe in the original vitamin tablet is 1.61mg (equation 10). From the standard deviations of the slope and intercept of the calibration plot, and the average deviation of the three unknown Fe absorbances, the error of Fe concentration in the unknown is 0.174 (equation ). The error of final calculated amount of Fe in the vitamin tablet is 0.174 (equation