Iodine reacts with mesitylene to form a complex with an absorption maximum at 332 nm in

Chapter 18, Problem 18-12

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Iodine reacts with mesitylene to form a complex with an absorption maximum at 332 nm in CCl4 solution: Iodine Mesitylene Complex (a) Given that the product absorbs at 332 nm, but neither reactant has significant absorbance at this wavelength, use the equilibrium constant, K, and Beers law to show that where A is the absorbance at 332 nm, is the molar absorptivity of the complex at 332 nm, [mesitylene] is the concentration of free mesitylene, and [I2]tot is the total concentration of iodine in the solution ( [I2] [complex]). The cell pathlength is 1.000 cm. (b) Spectrophotometric data for this reaction are shown in the table. Because [mesitylene]tot >> [I2], we can say that [mesitylene] [mesitylene]tot. Prepare a graph of A/([mesitylene][I2]tot) versus A/[I2]tot and find the equilibrium constant and molar absorptivity of the complex. Absorbance [Mesitylene]tot (M) [I2]tot (M) at 332 nm 1.690 7.817 105 0.369 0.921 8 2.558 104 0.822 0.633 8 3.224 104 0.787 0.482 9 3.573 104 0.703 0.390 0 3.788 104 0.624 0.327 1 3.934 104 0.556 SOURCE: P. J. Ogren and J. R. Norton, Applying a Simple Linear Least-Squares Algorithm to Data with Uncertainties in Both Variables, J. Chem. Ed. 1992, 69, A130. 1