Hydrazine has been employed as a reducing agent for metals. Using standard reduction potentials, predict whether the following metals can be reduced to the metallic state by hydrazine under standard conditions in acidic solution: (a) \(\mathrm{Fe}^{2+},(\mathbf{b}) \mathrm{Sn}^{2+},(\mathbf{c}) \mathrm{Cu}^{2+},(\mathbf{d}) \mathrm{Ag}^{+},(\mathbf{e}) \mathrm{Cr}^{3+},(\mathbf{f}) \mathrm{Co}^{3+}\)

The standard reduction potential of hydrazine in an acidic solution is given by the following equation: \( N_2H_4 + 4 H^+ + 4 e^- \rightarrow N_2 + 4 H_2O \) For this equation, the standard reduction potential, \(E^0\), is +0.76 V.

The standard reduction potentials for the given metal ions are as follows: (a) \( \mathrm{Fe}^{2+} + 2 e^- \rightarrow \mathrm{Fe} \), \(E^0 = -0.44 \, V\) (b) \( \mathrm{Sn}^{2+} + 2 e^- \rightarrow \mathrm{Sn} \), \(E^0 = -0.14 \, V\) (c) \( \mathrm{Cu}^{2+} + 2 e^- \rightarrow \mathrm{Cu} \), \(E^0 = +0.34 \, V\) (d) \( \mathrm{Ag}^{+} + e^- \rightarrow \mathrm{Ag} \), \(E^0 = +0.80 \, V\) (e) \( \mathrm{Cr}^{3+} + 3 e^- \rightarrow \mathrm{Cr} \), \(E^0 = -0.74 \, V\) (f) \( \mathrm{Co}^{3+} + 3 e^- \rightarrow \mathrm{Co} \), \(E^0 = -0.29 \, V\)

To determine whether hydrazine can reduce the metals, compare the standard reduction potentials of hydrazine and the metal ions. If the standard reduction potential of metal ion is lower than that of hydrazine (i.e., more negative), hydrazine can reduce the metal ion to its metallic state. (a) \(E^0_\mathrm{Hydrazine} > E^0_\mathrm{Fe^{2+}}\), so hydrazine can reduce iron(II) ions to iron. (b) \(E^0_\mathrm{Hydrazine} > E^0_\mathrm{Sn^{2+}}\), so hydrazine can reduce tin(II) ions to tin. (c) \(E^0_\mathrm{Hydrazine} > E^0_\mathrm{Cu^{2+}}\), so hydrazine can reduce copper(II) ions to copper. (d) \(E^0_\mathrm{Hydrazine} < E^0_\mathrm{Ag^{+}}\), so hydrazine cannot reduce silver(I) ions to silver. (e) \(E^0_\mathrm{Hydrazine} > E^0_\mathrm{Cr^{3+}}\), so hydrazine can reduce chromium(III) ions to chromium. (f) \(E^0_\mathrm{Hydrazine} > E^0_\mathrm{Co^{3+}}\), so hydrazine can reduce cobalt(III) ions to cobalt.

Based on the comparison of reduction potentials, hydrazine can reduce the following metal ions to their metallic state: (a) iron(II), (b) tin(II), (c) copper(II), (e) chromium(III), and (f) cobalt(III). However, hydrazine cannot reduce silver(I) ions to silver under standard conditions in an acidic solution.