problem set 2 key - Chemistry 312 Please turn in on your...

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Chemistry 312 Please turn in on your own paper and individually. Problem Set 2 (Due Friday, July 8, 2011) 1. Answer the following questions about the Pourbaix diagram shown below a. Is MnO 4 a stronger oxidant at pH 8 or pH 2? Explain your choice. At pH 2, MnO 4 has a larger positive potential than it does at pH 8. This matters because stronger oxidants have a higher positive potentials (MnO 4 reduces to MnO 2 ). b. Is MnO 2 (s) easier to reduce at pH 2 or pH 10? How do the half-reactions differ at pH 2 vs. pH 10? Write a balanced equation for each. When MnO 2 reduces, it is acting as an oxidant. Following the same reasoning as part a, the stronger oxidant has a higher positive potential; in this case, it is MnO 2 at pH 2. At pH 2, MnO 2 reduces to Mn 2+ (balanced reaction: 4 H + + 2 e + MnO 2 Mn 2+ + 2 H 2 O); at pH 10, MnO 2 reduces to Mn 2 O 3 (balanced reaction: H 2 O + 2 e + 2 MnO 2 Mn 2 O 3 + 2 OH ). c. What reaction occurs across the line labeled “a”? Is this a redox reaction? Give a justification. 3 Mn 2 O 3 + H 2 O + 2 e 2 Mn 3 O 4 + 2 OH ; this is a redox reaction (a reduction reaction, actually) because one species is gaining electrons. Note that the reverse reaction could also
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This note was uploaded on 01/19/2012 for the course CHEM 312 taught by Professor Staff during the Summer '08 term at University of Washington.

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problem set 2 key - Chemistry 312 Please turn in on your...

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