Solved: Describing a Voltaic CellThe oxidation–reduction

Chapter , Problem 2PE

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Problem 2PE

Describing a Voltaic Cell

The oxidation–reduction reaction

Cr2O72–(aq) + 14 H+(aq) + 6 I-(aq) → 2 Cr3+(aq) + 3 I2(s) + 7 H2O(l)

is spontaneous. A solution containing K2Cr2O7 and H2SO4 is poured into one beaker, and a solution of KI is poured into another. A salt bridge is used to join the beakers. A metallic conductor that will not react with either solution (such as platinum foil) is suspended in each solution, and the two conductors are connected with wires through a voltmeter or some other device to detect an electric current. The resultant voltaic cell generates an electric current. Indicate the reaction occurring at the anode, the reaction at the cathode, the direction of electron migration, the direction of ion migration, and the signs of the electrodes.

The two half-reactions in a voltaic cell are

Zn(s) → Zn2+(aq) + 2 e– (electrode = Zn)

ClO3–(aq) + 6 H+(aq) + 6 e–→ Cl–(aq) + 3 H2O(l) (electrode = Pt)

(a) Indicate which reaction occurs at the anode and which at the cathode., (b) Does the zinc electrode gain, lose, or retain the same mass as the reaction proceeds? (c) Does the platinum electrode gain, lose, or retain the same mass as the reaction proceeds? (d) Which electrode is positive?

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