Question

$\textbf{The orange colour of } \text{K}_2\text{Cr}_2\text{O}_7 \textbf{ and purple colour of KMnO}_4 \textbf{ is due to}$

• A. d$\rightarrow$d transition in K$_2$Cr$_2$O$_7$ and charge transfer transitions in KMnO$_4$.
• B. d$\rightarrow$d transition in KMnO$_4$ and charge transfer transitions in K$_2$Cr$_2$O$_7$.
• C. Charge transfer transition in both.
• D. d$\rightarrow$d transition in both.

Answer 1

The Correct Option is C

The question seeks the origin of the colors in K₂Cr₂O₇ (orange) and KMnO₄ (purple), with options relating to electronic transitions. The following explanation clarifies the coloration:

1. Charge Transfer Transition:
   • Compound coloration is typically attributed to electronic transitions.
   • Inorganic compounds exhibit two main transition types: d-d and charge transfer.
   • A charge transfer transition involves electron movement between the metal and ligands. These transitions are potent, due to inter-element electron transfer, and are characteristic of highly colored compounds like K₂Cr₂O₇ and KMnO₄.
2. d-d Transition:
   • This transition occurs when an electron moves between d-orbitals of a transition metal.
   • d-d transitions are weak, involving electrons within the same atom without altering chemical bonds.
   • They are commonly observed in complexes with partially filled d orbitals.
3. Chromate and Permanganate Colors:
   • K₂Cr₂O₇ (Potassium Dichromate): Its orange hue results from charge transfer transitions between chromium and oxygen atoms.
   • KMnO₄ (Potassium Permanganate): Its intense purple color stems from similar charge transfer transitions from the ligand to manganese.

Consequently, both compounds' colors are explained by charge transfer transitions within their molecular structures.

The correct answer is: Charge transfer transition in both.