Question

Zn\(^{2+}\) salts are colourless. Why?

Hint:

The color of transition metal salts depends on the presence of unpaired electrons in the \( d \)-orbitals that can absorb visible light.

Answer 1

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.