Problem 123 - A Complete Resource Book in Chemistry for JEE Main

Question

Number of electrons transferred in each case when \(\mathrm{KMnO}_{4}\) acts as an oxidizing agent to give \(\mathrm{MnO}_{2}\), \(\mathrm{Mn}^{2+}, \mathrm{Mn}(\mathrm{OH})_{2}\) and \(\mathrm{MnO}_{4}^{2-}\) are respectively \(\quad[\mathbf{2 0 0 2}]\) (a) \(1,3,4\) and 5 (b) \(4,3,1\) and 5 (c) \(5,4,3\) and 1 (d) \(3,5,4\) and 1

Step-by-Step Solution

Answer

The correct answer is (d) 3, 5, 4, and 1.

Step 1: Determine the oxidation state of Mn in KMnO4

The oxidation state of potassium (K) is +1 and oxygen (O) is typically -2. Let's calculate the oxidation state of Mn in \( \text{KMnO}_4 \):\[ +1 + \text{Mn} + 4(-2) = 0 \]This simplifies to \(+1 + \text{Mn} - 8 = 0\), giving us \(\text{Mn} = +7\).

Step 2: Calculate the change in oxidation state to MnO2

In \( \text{MnO}_2 \), the oxidation state of oxygen is -2, so the oxidation state of Mn is calculated as follows:\[ \text{Mn} + 2(-2) = 0 \]This gives \( \text{Mn} = +4 \).Comparing the oxidation state of Mn in \(\text{KMnO}_4\) (+7) to that in \(\text{MnO}_2\) (+4), the change is \(+7 - +4 = 3\). Hence, 3 electrons are transferred.

Step 3: Calculate the change in oxidation state to Mn2+

For \( \text{Mn}^{2+} \), the Mn has an oxidation state of +2.From \(\text{KMnO}_4\) at +7 to \( \text{Mn}^{2+} \) at +2, the change is \(+7 - +2 = 5\), so 5 electrons are transferred.

Step 4: Calculate the change in oxidation state to Mn(OH)2

In \( \text{Mn(OH)}_2 \), the oxidation state of OH is -1, so the oxidation state of Mn must be +2 to balance it:\[ \text{Mn} + 2(-1) = 0 \]The oxidation state of Mn is therefore +2. From \(\text{KMnO}_4\) at +7 to \(\text{Mn(OH)}_2\) at +2, 5 electrons are transferred.

Step 5: Calculate the change in oxidation state to MnO4^2-

In \(\text{MnO}_4^{2-}\), the oxidation state of oxygen remains -2, and overall, the ion carries a -2 charge:\[ \text{Mn} + 4(-2) = -2 \]Solving gives \( \text{Mn} = +6 \). From \(\text{KMnO}_4\) at +7 to \(\text{MnO}_4^{2-}\) at +6, 1 electron is transferred.

Step 6: Compile the number of electrons transferred for each reaction

Summarizing results, the number of electrons transferred when \( \text{KMnO}_4 \) gets reduced to each of the products is as follows:- To \(\text{MnO}_2\), 3 electrons are transferred.- To \(\text{Mn}^{2+}\) or \(\text{Mn(OH)}_2\), 5 electrons are transferred.- To \(\text{MnO}_4^{2-}\), 1 electron is transferred.Hence, the correct sequence is \(3, 5, 5, 1\), matching option (d).

Key Concepts

Electron Transfer

Electron transfer is a core concept in oxidation-reduction reactions. It involves the movement of electrons from one species to another when chemical reactions occur. Understanding this concept is crucial to grasp oxidation-reduction or redox reactions.
In a redox process, one element loses electrons while another gains them, highlighting their changing oxidation states. This flow of electrons from one species to another balances the charges, ensuring the reaction's overall charge remains neutral. The number of electrons transferred indicates how complete the redox reaction is.

• Electron loss is termed oxidation.
• Electron gain is termed reduction.

For example, when potassium permanganate (woord{KMnO4}) acts as an oxidizing agent and reacts with different substances, it results in varied electron transfers, indicating different levels of reduction.
The reactions explored, such as
5wor{MnO}_2 and
5wor{Mn}^{2+}, exemplify how these transfers change the manganese factor's oxidation state.

Oxidation State

The oxidation state or oxidation number of an atom in a molecule or ion describes its degree of oxidation, guiding the electron transfer during reactions.
This number can vary depending on the substance it reacts with. It acts like a bookkeeping method, helping us keep track of how many electrons an atom has gained, lost, or shared during a reaction.

• An increase in oxidation state indicates oxidation (loss of electrons).
• A decrease represents reduction (gain of electrons).

Consider
5wrdd{KMnO}
5>