The source is a battery-operated tungsten lamp that provides a "white" light for operation in the visible. A mirror M1 sends a beam of light from this source through the entrance slit S1 into the monochromator. This beam is reflected to a quartz prism by the collimating mirror M2. The prism P is of the so-called Littrow type so that the light undergoes refraction on entering the front surface, is relected from the solvered back surface, and undergoes a second refraction on leaving the prism. When the prism is rotated, a narrow band of light, which is nearly monochromatic at any desired wavelength in the visible, can be passed throught the exit slit S2. A sample cell, with plane parallel windows, is mounted in the sample compartment between the exit slit and the photodetector D. All light that is transmitted by the sample falls on the detector whose photocurrent is amplified and recorded. The magnitude of the photocurrent is proportional to the intensity of the transmitted light.

a. Suppose you were given an aqueous solution of Ru(bipy)32+ of unknown concentration [x] in units of moles/liter. Suppose also that you had available 10 g of pure Ru(bipy) 32+. Carefully explain what operations you would undertake to determine the value of [x]. Some possibly useful information follows: For Beer's law, I = Ioe(-ecl); Ru(bipy) 32+ has the chemical formula Ru(C10H8N2) 3, and the atomic weights are Ru = 101.07 g/mole, C = 12.011 g/mole, H = 1.008 g/mole, and N = 14.007 g/mole.

B. Prepare a set of instructions for a beginning student explaining how you would use the instrument shown in the figure to obtain an absorption spectrum of an aqueous solution of Ru(bipy)32+.

C. The ionic species tris (2,2’-bipyridine) ruthenium(II) Ru(bipy) 32+ has the structure

and is chiral. Explain briefly how to resolve a racemic mixture of Ru(bipy) 32+ into its two enantiomers, and how to make sure that your separation procedure has worked.

The exact enantiomer recovered can be determined by verifying which direction the plane-polarized light is rotated (using a polarimeter) and comparing this to known experimental results.

9. * (1993 F B1E) IR absorption. The photochemical decomposition of HI in the gas phase at 266 nm results in the production of H2 and I2 in the gas phase. It is found experimentally that two molecules of HI are decomposed per photon absorbed. This information suggests two possible mechanisms in which the heat released is indicated for each step (recall that negative DH corresponds to positive heat release):

 Mechanism I DH (kcal/mol) hn + HI ----> H + I (fill in from part D) I + HI ----> H + I2 +35 H + H + M ----> H2 + M -104 Mechanism II DH (kcal/mol) hn + HI ----> H + I (fill in from part D) H + HI ----> H2 + I -33 I + I + M ----> I2 + M -36

In each mechanism M represents a third body that stabilizes the collision process.

Would it be possible to follow concentrations of reactants and products by infrared absorptions? Discuss.