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

To understand the preparation of potassium permanganate (\( KMnO_4 \)) from manganese dioxide (\( MnO_2 \)), we need to look at the multi-step reaction process involved. This involves the following steps: 

1. The first step in the process involves heating manganese dioxide (\( MnO_2 \)) with potassium hydroxide (\( KOH \)) and an oxidizing agent like potassium nitrate (\( KNO_3 \)) or oxygen. The general reaction is:

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

As per the question, the product of this first step is potassium manganate (\( K_2MnO_4 \)). This is an intermediate in the preparation of potassium permanganate.

1. In the subsequent step, the produced potassium manganate (\( K_2MnO_4 \)) is oxidized further to form potassium permanganate (\( KMnO_4 \)). This is usually done by bubbling carbon dioxide or by further chemical oxidation:

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

With this understanding, we can conclude that the correct product formed in the first step is potassium manganate (\( K_2MnO_4 \)).

Let's rule out the incorrect options:

• \( K_4[{Mn(OH)}_6] \): This chemical formula does not correspond to any known products in the formation of potassium permanganate.
• \( K_3{MnO}_4 \): Potassium manganate's formula is \( K_2{MnO}_4 \), not \( K_3{MnO}_4 \).
• \( KMnO_4 \): This is the final product of the process, not the product of the first step.

Therefore, the correct answer is \( K_2{MnO}_4 \).

Answer 2

Preparation of Potassium Permanganate (\( \text{KMnO}_4 \)) from Manganese Dioxide (\( \text{MnO}_2 \)) 

Given: The preparation of potassium permanganate involves two steps. In the first step, manganese dioxide (\( \text{MnO}_2 \)) reacts with potassium hydroxide (KOH) and potassium nitrate (\( \text{KNO}_3 \)) to form potassium manganate (\( \text{K}_2\text{MnO}_4 \)).

Step 1: The reaction

The reaction is as follows: \[ \text{MnO}_2 + 4 \text{KOH} + 2 \text{KNO}_3 \to \text{K}_2\text{MnO}_4 + 2 \text{H}_2\text{O} \] - Manganese dioxide reacts with potassium hydroxide and potassium nitrate to produce potassium manganate and water.

Conclusion:

The product of the first step is \( \boxed{\text{K}_2\text{MnO}_4} \), which corresponds to option (4).