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

Answer: (C)

Charge transfer transition in both.

Answer 2

The colors observed in $K_2Cr_2O_7$ and $KMnO_4$ arise from electronic transitions within the compounds:

Charge Transfer Transitions: Charge transfer transitions involve the movement of an electron from a filled orbital (usually a ligand) to an empty orbital of a metal ion.

In the case of $K_2Cr_2O_7$, the orange color is primarily due to the charge transfer transition associated with the $Cr^{6+}$ ion.

In $KMnO_4$, the purple color results from a similar charge transfer transition involving the $Mn^{7+}$ ion.

Summary of Transitions: Both compounds exhibit charge transfer transitions rather than d → d transitions, which are more common in transition metal complexes with partially filled d orbitals.

Thus, the correct explanation for the observed colors in both $K_2Cr_2O_7$ and $KMnO_4$ is: Charge transfer transition in both.