Question

Copper has an exceptionally positive \( E^\circ_{\text{M}^{2+}/\text{M}} \) value, why?

Answer 1

Copper has an exceptionally positive \( E^\circ_{\text{M}^{2+}/\text{M}} \) value because copper's \( 3d^{10} 4s^1 \) electron configuration makes its \( Cu^{2+} \) ion highly stable compared to the other transition metal ions. When copper undergoes oxidation from \( Cu \) to \( Cu^{2+} \), it loses electrons, and the reaction becomes more favorable due to the relatively low tendency of copper to lose electrons.
Additionally, the stable \( 3d^{10} \) configuration of \( Cu^+ \) gives it a strong tendency to stay in the +1 oxidation state, making copper less likely to oxidize further to +2.
Thus, the positive \( E^\circ_{\text{M}^{2+}/\text{M}} \) value reflects the fact that the copper ion is more stable in its lower oxidation state, giving it a tendency to resist further oxidation.

Answer 2

The element that is a strong reducing agent in the +2 oxidation state is Zinc (Zn). Zinc has a relatively low \( E^\circ_{\text{Zn}^{2+}/\text{Zn}} \) value of \(-0.76 \, \text{V}\), which means it readily loses electrons to form \( Zn^{2+} \). The more negative the \( E^\circ \) value, the stronger the reducing agent, because it indicates a greater tendency to donate electrons.
In the +2 oxidation state, zinc acts as a strong reducing agent, easily donating electrons to reduce other species.

Answer 3

Zinc \(^{2+}\) salts are colorless because the \( Zn^{2+} \) ion has a completely filled \( 3d^{10} \) electron configuration. The lack of any unpaired electrons in the \( 3d \) orbitals prevents the absorption of visible light, which is required for color. As a result, zinc salts do not absorb visible wavelengths of light, leading to the colorless appearance of \( Zn^{2+} \) solutions.
In other transition metal ions, the unfilled \( d \)-orbitals allow electronic transitions that absorb specific wavelengths of visible light, giving the solution a color. Since \( Zn^{2+} \) does not have such transitions, it remains colorless.