Q1: The complexes of Fe+2 with 1, 10- phenanthroline has a molar absorptivity of about 11,000 L/mol cm in water at 510 nm. A 20 ml water sample thought to contain Fe+2 is mixed with an excess of 1,10- phenanthroline. Acetic acid, sodium acetate, and hydroxylamine are also added to buffer the solution and assure that all the iron is reduced to Fe(II). This mixture is diluted with distilled water to a total volume of 50 ml , and the final solution is found to give an absorbance of 0.762 at 510 nm when using a 1 cm cuvette.
a. If it is assumed that there are no absorbing species in this solution other than the Fe+2complex with 1, 10- phenanthroline, what was the concentration of Fe+2
In the original sample?
b. Discuss how the prescence of other species that also absorb at 510 nm would have affected the accuracy of this measurement. Would a positive error or negative error be obtained?
Q2; Copper can be measured by both atomic emission and absorption spectroscopy .
a. In a copper measurement that is made by atomic emission spectroscopy, a blank solution that is measured intensity at 216.6 nm of 0.2 unit. A 1 ppm Cu+2 solution that is measured under the same conditions gives an emission intensity of 18.4 units and unknown sample produces an emission intensity of 12.7 units. What is the concentration of copper in the sample?
b. Copper measurement is made by atomic absorption spectroscopy of the same sample and standard. The same blank solution gives an absorbance reading 0.004 units at 216.6 nm and the 1 ppm Cu+2standard has absorbance of 0.305. What do you predict will be absorbance the unknown solution?