Question

Preparation of potassium permanganate from MnO\(_2\) involves a two-step process in which the 1^st step is a reaction with KOH and KNO\(_3\) to produce:

• A. \( K_4[{Mn(OH)}_6] \)
• B. \( K_3{MnO}_4 \)
• C. \( {KMnO}_4 \)
• D. \( K_2{MnO}_4 \)

Hint:

In the first step of preparing potassium permanganate, potassium manganate (\( {K}_2{MnO}_4 \)) is formed by reacting manganese dioxide with potassium hydroxide and potassium nitrate. This is then further oxidized to potassium permanganate.

Answer 1

The Correct Option is D

The preparation of potassium permanganate (\( KMnO_4 \)) from manganese dioxide (\( MnO_2 \)) is a multi-step reaction. The process involves the following:

1. Initially, manganese dioxide (\( MnO_2 \)) is heated with potassium hydroxide (\( KOH \)) and an oxidizing agent such as potassium nitrate (\( KNO_3 \)) or oxygen. The reaction is represented as:

\(MnO_2 + 2KOH + \frac{1}{2}O_2 \rightarrow K_2MnO_4 + H_2O\)

The product of this initial stage, as indicated, is potassium manganate (\( K_2MnO_4 \)), which serves as an intermediate in potassium permanganate synthesis.

1. Subsequently, the potassium manganate (\( K_2MnO_4 \)) undergoes further oxidation to yield potassium permanganate (\( KMnO_4 \)). This is typically achieved by bubbling carbon dioxide through the solution or through additional chemical oxidation methods:

\(3K_2MnO_4 + 2CO_2 \rightarrow 2KMnO_4 + 2K_2CO_3 + MnO_2\)

Based on these steps, the product formed in the first reaction is confirmed to be potassium manganate (\( K_2MnO_4 \)).

The following options are incorrect:

• \( K_4[{Mn(OH)}_6] \): This formula is not a recognized product in the synthesis of potassium permanganate.
• \( K_3{MnO}_4 \): The correct formula for potassium manganate is \( K_2{MnO}_4 \), not \( K_3{MnO}_4 \).
• \( KMnO_4 \): This represents the final product, not the product of the initial step.

Consequently, the correct product of the first step is \( K_2{MnO}_4 \).