name section date Pre-Laboratory Assignment 1. Read an authoritative source for a discussion of spectrophotometry. 2. The two components of the solution you will be making in this experiment must be used with great care. List these two substances and describe the problems associated with each. (2) Convert percent transmittances to equiva- lent absorbances, using Equation 4. ate of th 3. 1,10-Phenanthroline forms a bright red complex with iron(II). The complex has an analytical wave- length of 510 nm and has a high molar absorptivity. Hydroxylamine hydrochloride is added to keep the iron in a reduced +2 state, and the pH is controlled us- ing an acetate buffer. A series of iron(II)-phen- anthroline solutions were made by adding various amounts of 4.300 x 10-4M Fe2+ to 5 mL each of hydroxylamine hydrochloride, acetate buffer, and 1,10-phenanthroline. Distilled water was added to make the total volume of each solution 50.00 mL. The percent transmittance of each solution was read, us- ing a blank containing everything but the iron(II) solu- tion. Data for the determination are (3) Prepare a Beer's law plot for [Fe(phenanthroline)3]2+, using the data obtained in (1) and (2). Draw a best straight line through the data points. (4) A solution containing an unknown amount. of iron(II) was treated with hydroxylamine hydrochlo- ride, acetate buffer, and 1,10-phenanthroline as de- scribed above. The percent transmittance of the sam- ple at 510 nm was 52.4 when read against a blank containing all but the iron(II) solution. Determine the molar concentration of iron(II) in the unknown. (5) Calculate the molar absorptivity for volume of stock volume of stock solution, mL %T solution, mL %T 1.00 80.35 7.00 21.78 2.00 64.71 9.00 14.09 5.00 33.65 10.00 11.32 (1) Calculate the molar concentration of [Fe(phenanthroline)3]2+ in each solution. [Fe(phenanthroline)3]2+. Assume a 1.00-cm path- length.