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homework_problem_set_2_key - Chemistry 312 Problem Set#2...

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Chemistry 312 Problem Set #2 Key Due Fri.. Jan. 29, 2010 1. Answer the following questions about the Pourbaix diagram shown below a. Is MnO 4 a stronger oxidant at pH= 8 or pH= 2? At pH= 2 since the potential at which it is converted to MnO 2 is more positive at this pH. When MnO 4 is acting as an oxidant it becomes reduced to form MnO 2 . b. Is MnO 2 (s) easier to reduce at pH= 2 or pH= 10? At pH= 2 since the potential at which it is reduced (proceeding down in the Pourbaix diagram) is more positive at this pH. How do the half rxns differ at pH= 2 vs. pH= 10? At pH= 2 MnO 2 is converted to Mn +2 , while at pH= 10 it converts to Mn 2 O 3 . Write a balanced eqn for each. c. a. d. b.
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At pH= 2: MnO 2 + 2e + 4H + Mn +2 + 2H 2 O At pH= 10: 2MnO 2 + 2e + H 2 O Mn 2 O 3 + 2OH c. What reaction occurs across the line labeled “a”? Is this a redox reaction? The redox rxn: 3Mn 2 O 3 + 2e + H 2 O 2Mn 3 O 4 + 2OH d. What reaction occurs across the line labeled “b”? Is this a redox reaction? The redox rxn: MnO 2 + 2e + 4H + Mn +2 + 2H 2 O e. What reaction occurs across the line labeled “c”? Is this a redox reaction?
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