A student measures the potential of a cell made up with \(1 \mathrm{M}\) CuSO,
in one solution and \(1 \mathrm{M} \mathrm{AgNO}_{3}\) in the other. There is a
Cu electrode in the CuSO, and an Ag electrode in the AgNO, and the cell is set
up as in Figure \(32.1 .\) She finds that the potential, or voltage, of the
cell, \(E_{\text {cell }}^{0}\), is \(0.45 \mathrm{V}\), and that the Cu electrode
is negative.
a. At which electrode is oxidation occurring?
b. Write the equation for the oxidation reaction.
c. Write the equation for the reduction reaction.
d. If the potential of the silver, silver ion electrode, \(E_{A
g^{\prime}}^{0}\) angle is taken to be \(0.000 \mathrm{V}\) in oxidation or
reduction, what is the value of the potential for the oxidation reaction,
\(E_{\mathrm{Cu}, \mathrm{Cu}^{2+} \text { 'arid }}\) ? \(E_{\text {cell
}}^{0}=E_{\text {oxid }}^{0}+E_{\text {red }}^{0}\).
e. If \(E_{A g^{+} A g \text { red }}^{0}\) equals \(0.80 \mathrm{V}\), as in
standard tables of electrode potentials, what is the value of the potential of
the oxidation reaction of copper, \(E_{\cos a^{2}+a x i d}^{0}\)?
f. Write the net ionic equation for the spontaneous reaction that occurs in
the cell that the student studied.
g. The student adds \(6 \mathrm{M} \mathrm{NH}_{3}\) to be CuSO, solution until
the \(\mathrm{Cu}^{2+}\) ion is ecstatically all converted to
\(\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}^{2+}\) ion. The voltage of the
cell, \(E_{\text {cell }}\) goes up to \(0.92 \mathrm{V}\) and the Cu clectrode is
still negative. Find the residual concentration of \(\mathrm{Cu}^{2+}\) ion in
the cell. (Use Eq. 3.)
h. In Part \(g,\left[C u\left(N H_{3}\right)_{4}^{2+}\right]\) is about \(0.05
\mathrm{M},\) and \(\left[\mathrm{NH}_{3}\right]\) is about \(3 \mathrm{M}\). Given
those values and the result
in Part \(1 \mathrm{g}\) for \(\left[\mathrm{Cu}^{2+}\right],\) calculate
\(\mathrm{K}\) for the reaction:
$$\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}^{2+}(\mathrm{aq})
\rightleftarrows \mathrm{Cu}^{2+}(\mathrm{aq})+4
\mathrm{NH}_{3}(\mathrm{aq})$$
