Question

When \(MnO_2\) is heated with \(PbO_2\) and conc. \(HNO_3\), pink colour is obtained due to formation of:

• A. \(KMnO_4\)
• B. \(HMnO_4\)
• C. \(Pb(MnO_4)_2\)
• D. \(PbMnO_4\)

Hint:

Pink/purple colour in acidic medium \(\rightarrow\) \(HMnO_4\) (permanganic acid). \(PbO_2\) + conc. \(HNO_3\) is a powerful oxidizing combination.

Answer 1

The Correct Option is B

To determine why a pink color is formed when \(MnO_2\) is heated with \(PbO_2\) and concentrated \(HNO_3\), let's analyze the chemical reaction involved:

1. The key reaction that takes place involves the oxidation of \(MnO_2\) in the presence of concentrated \(HNO_3\) and a strong oxidizing agent like \(PbO_2\).
2. The reaction proceeds as follows: \(2MnO_2 + 2PbO_2 + 4HNO_3 \rightarrow 2HMnO_4 + 2Pb(NO_3)_2 + 2H_2O\). In this reaction, the oxidation number of manganese increases from +4 in \(MnO_2\) to +7 in \(HMnO_4\).
3. \(HMnO_4\) (or permanganic acid) imparts a pink color to the solution.

Thus, the pink color observed upon heating \(MnO_2\) with \(PbO_2\) and concentrated \(HNO_3\) is due to the formation of \(HMnO_4\).

Therefore, the correct answer is \(HMnO_4\).

Let's rule out the other options:

• \(KMnO_4\): This compound is not formed in this reaction as neither potassium nor its compounds are involved.
• \(Pb(MnO_4)_2\): While this is a possible permanganate species, the pink color described matches that provided by the permanganic acid \(HMnO_4\), not a lead compound.
• \(PbMnO_4\): This compound does not relate to the observed color change in the reaction.

In summary, the observed pink color is characteristic of \(HMnO_4\), making it the correct choice.