1. Cars can use electricity generated by hydrogen-oxygen fuel cells. Which half-

Question

1. Cars can use electricity generated by hydrogen-oxygen fuel cells. Which half-reaction occurs at the cathode of the cell, which occurs at the anode? What is the net reaction of hydrogen-oxygen fuel cells? Write the balanced equations.

2. Read “Applying Chemical Principles: Sacrifice!” in Chapter 19 of the text. Answer the questions below.

The corrosion of a metal object, such as a boat or underground tank, can be prevented by attaching a small piece of other metal (called “sacrificial” anode) to the metal object. In order to prevent corrosion of an underground metal pipe made of iron, which metal, zinc or tin, could serve as a “sacrificial” anode? Explain. Use appropriate standard reduction potentials to support your argument.

This is for extra credit for chem 2, please check answers for rating.

Explanation / Answer

1.

H2 - O2 fuel cell

Half cell reaction at cathode:

O2 (g) + 2 H2O (l) + 4e -------> 4 OH- (aq.)

Half cell reaction at anode:

2 H2 (g) + 4 OH- (aq.) --------------> 4 H2O (l) + 4e

Overall cell reaction:

2 H2 (g) + O2 (g) -------------> 2 H2O (l)

2.

E0Sn2+/Sn = - 0.14 V

E0Zn2+/Zn = - 0.76 V

E0Fe2+/Fe = - 0.44 V

Since the standard reduction potential of Zn2+ is less than that of Fe2+,

Zn acts as sacrificail anode for iron pipe.

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