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

Why Are Zinc ²⁺ Salts Colorless? 

Zinc salts, specifically those containing the \( \text{Zn}^{2+} \) ion, are colorless due to their electronic configuration.

The electronic configuration of a \( \text{Zn}^{2+} \) ion is:

\( 1s^2\,2s^2\,2p^6\,3s^2\,3p^6\,3d^{10} \)

This configuration shows a completely filled \( 3d \) subshell, with no unpaired electrons.

In transition metal ions, color typically arises from \( d \rightarrow d \) electronic transitions—when electrons jump between split \( d \)-orbital energy levels by absorbing visible light. However, in \( \text{Zn}^{2+} \), these transitions are not possible because:

• The \( 3d \)-orbitals are fully filled.
• No vacant \( d \)-orbitals are available for electron transitions.

As a result, \( \text{Zn}^{2+} \) ions do not absorb visible light, and their salts appear colorless in solution.