Question

The correct descending order of oxidizing power of the following is

• A. Cr\textsubscript{2}O\textsubscript{7}\textsuperscript{2--} $>$ MnO\textsubscript{4}\textsuperscript{--} $>$ VO\textsubscript{2}\textsuperscript{+}
• B. MnO\textsubscript{4}\textsuperscript{--} $>$ Cr\textsubscript{2}O\textsubscript{7}\textsuperscript{2--} $>$ VO\textsubscript{2}\textsuperscript{+}
• C. VO\textsubscript{2}\textsuperscript{+} $>$ MnO\textsubscript{4}\textsuperscript{--} $>$ Cr\textsubscript{2}O\textsubscript{7}\textsuperscript{2--}
• D. MnO\textsubscript{4}\textsuperscript{--} $>$ VO\textsubscript{2}\textsuperscript{+} $>$ Cr\textsubscript{2}O\textsubscript{7}\textsuperscript{2--}
• E. Cr\textsubscript{2}O\textsubscript{7}\textsuperscript{2--} $>$ VO\textsubscript{2}\textsuperscript{+} $>$ MnO\textsubscript{4}\textsuperscript{--}

Hint:

In the first transition series oxoanions, oxidizing power generally increases across the period from Left to Right (V to Cr to Mn). More protons in the nucleus make the high oxidation state more "desperate" for electrons.

Answer 1

The Correct Option is B

Concept: The oxidizing power of oxoanions of transition metals depends on their reduction potentials, which are influenced by the stability of the lower oxidation states.
• Oxidation States: In MnO\textsubscript{4}\textsuperscript{--}, Mn is in +7. In Cr\textsubscript{2}O\textsubscript{7}\textsuperscript{2--}, Cr is in +6. In VO\textsubscript{2}\textsuperscript{+}, V is in +5.
• Electrode Potentials ($E^0$): Higher positive reduction potential values indicate a stronger oxidizing agent.

Step 1: Compare the standard reduction potentials. - For $MnO_4^- / Mn^{2+}$, $E^0 \approx +1.51$ V. - For $Cr_2O_7^{2-} / Cr^{3+}$, $E^0 \approx +1.33$ V. - For $VO_2^+ / VO^{2+}$, $E^0 \approx +1.00$ V.

Step 2: Determine the order. Permanganate is the strongest oxidizer in this group because Manganese is highly unstable in the +7 state and has the highest affinity for electrons. Chromate follows, and Vanadate is the weakest of the three. Descending order: $MnO_4^- > Cr_2O_7^{2-} > VO_2^+$.