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Unformatted text preview: CHM 241 Spring 2011 Problem Set 7 Due April 25 Answer Key Exercises 17.4) Sketch the form of the vacant s* orbital of a dihalogen molecule and describe its role in the Lewis acidity of the dihalogens? Since the 2u* antibonding orbital is the LUMO for a X2 molecule, it is the orbital that accepts the pair of electrons from a Lewis base. 17.8) Given that 1.84 g of IF3 reacts with 0.93 g of [(CH3)4N]F to form a product X, (a) identify X, (b) use the VSEPR model to predict the shapes of IF, and the cation and anion in X 1.84 g/183.9 g/mol = 0.01 mol 0.93 g/93.1 g/mol = 0.01 mol a) X = IF4- +N(CH3)4 b) The shape of anion IF4- is square planar. The shape of cation (CH3)4N+ is tetrahedral. 17.23) With regard to the general influence of pH on the standard potentials of oxoanions, explain why the disproportionation of an oxyanion is often promoted by low pH? Fig 17.14 shows oxoanions tend to be more oxidizing at low pH. That implies lower oxidation states are in general less likely to disproportionate on thermodynamic grounds. On the other hand, the text shows on p. 435 that the kinetics may be more favorable at low pH. Therefore, when kinetics dominates, it is possible that lowering pH will promote the reaction. 18.4) Draw the Lewis structures of (b) XeO2F2? (c) XeO64-? b) c) 18.5) Give the formula and describe the structure of a noble gas species that is isostructural with (b) IBr2-? (c) BrO3-? b) Linear geometry. Isostructural with XeF2. c) Trigonal pyramidal geometry. Isostructural with XeO3. Problems A. Describe preparations for the following: a) KBrO3(s) (from Br2) 6 Br2 + 12 KOH 2 KBrO3 + 6 H2O + 10 KBr b) I2O5(s) (from HIO3) Dehydration of iodic acid at 200 C 2 HIO3 I2O5 + H2O c) BrF3 (from Br2) Br2 + 3 F2 2 BrF3 B. Upon adding BrCl to a hot aqueous solution of NaOH leads to formation of the sodium salts of three halogen-containing atoms. Rationalize the findings, and balance the equation. 2 BrCl 2 Cl- + Br- + BrO3- (in base) Expect disproportionation of dihalogen. Chloride is more electronegative. BrCl + 2 OH- BrO- + Cl- + H2O BrO- is unstable wrt disproportionation in base. BrO4- does not form because BrO3- is stable. 3 BrO- 2 Br- + BrO3- C. Identify the oxidation state(s) of iodine that is (are) unstable wrt disproportionation in basic solution, at pH = 14. I2 (ox st = 0) disproportionates in base to I- and IO3- in base. D. The following is a contour of an orbital from the MO scheme of XeF2. Is it the HOMO or the LUMO? Identify the atomic orbitals involved if the molecular axis is the z-axis. LUMO, antibonding. The only unfilled orbital in the scheme. * nb E. Describe the preparation of XeOF4 (from Xe). Xe + xssF2 XeF6 XeF6 + H2O XeOF4 + 2 HF ...
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This note was uploaded on 03/20/2012 for the course CHM 24100 taught by Professor Professordavidr.mcmillin during the Spring '10 term at Purdue.
- Spring '10