After passing a total charge of through an electrolytic cell containing of ( CuSO _ 4…

CHEMISTRY · Single correct · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry

Problem

After passing a total charge of

7.70 \times 10^{4}\,\text{C}

through an electrolytic cell containing

0.25\,\text{L}

1.0\,\text{M}

\text{CuSO}_{4}

(aq), a student scrapes only

1.8\,\text{g}

\text{Cu}(s)

from the cathode surface. Which of the following best explains the unexpectedly low percent yield of copper? (a) Some of the electric charge was dissipated as heat because of the internal resistance of the cell, leaving less charge available to reduce

\text{Cu}^{2+}

ions. (b) A portion of the current was instead used to reduce water, producing

\text{H}_2(g)

at the cathode. (c) The

0.25\,\text{L}

1.0\,\text{M}

\text{CuSO}_{4}

solution contained too few

\text{Cu}^{2+}

ions to yield the calculated mass of copper. (d)

\text{Cu}^{2+}

actually requires four electrons, not two, to be reduced to

\text{Cu}(s)

; using two electrons in the calculation overestimates the yield.

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