Question

Which of the following is an intramolecular redox reaction? (1) \(\mathrm{P}_{4}+\mathrm{NaOH} \longrightarrow \mathrm{H}_{3} \mathrm{PO}_{2}+\mathrm{PH}_{3}\) (2) \(2 \mathrm{Cu}^{+}(\mathrm{aq}) \longrightarrow \mathrm{Cu}+\mathrm{Cu}^{2-}\) (3) \(2 \mathrm{KClO}_{3} \longrightarrow 2 \mathrm{KC} 1+3 \mathrm{O}_{2}\) (4) \(4 \mathrm{HClO}_{3} \longrightarrow 3 \mathrm{HClO}_{4}+\mathrm{HCl}\)

Short answer

Reaction 4 \(4 \text{HClO}_{3} \rightarrow 3 \text{HClO}_{4} + \text{HCl} \) is an intramolecular redox reaction.

Step-by-step solution

- Understanding Intramolecular Redox Reaction

An intramolecular redox reaction is where oxidation and reduction occur within the same molecule.

- Analyze Reaction 1

Analyze the oxidation states of elements in \(\text{P}_{4} + \text{NaOH} \rightarrow \text{H}_{3}\text{PO}_{2} + \text{PH}_{3} \). Check if any element changes its oxidation state.

- Analysis of Reaction 2

Evaluate the oxidation states in \(2 \text{Cu}^{+} (\text{aq}) \rightarrow \text{Cu} + \text{Cu}^{2-} \). Note if any oxidation state change occurs within the same element.

- Analysis of Reaction 3

Observation of oxidation states in \(2 \text{KClO}_{3} \rightarrow 2 \text{KCl} + 3 \text{O}_{2} \). Detect oxidation and reduction in individual species.

- Analysis of Reaction 4

Consider the oxidation states transformations in \(4 \text{HClO}_{3} \rightarrow 3 \text{HClO}_{4} + \text{HCl} \). Identify elements undergoing oxidation and reduction within the same molecule.

- Compare Results

Compare the results of steps 2 to 5. Determine which reaction involves oxidation and reduction within the same molecule.

- Conclusion

Conclude the correct answer based on the identified intramolecular redox reaction.

Key concepts

Oxidation States

Oxidation states (or oxidation numbers) are a way to keep track of electrons during chemical reactions. They help you figure out how electrons are transferred. This is crucial for understanding redox reactions, including intramolecular redox reactions.

In a molecule, the oxidation state represents the degree of oxidation (loss of electrons) or reduction (gain of electrons) of an atom. The oxidation state is assigned based on a set of rules:

• The oxidation state of a free element is always 0. For example, in \(\text{P}_{4}\), phosphorus has an oxidation state of 0.
• For monoatomic ions, the oxidation state equals the charge of the ion. For example, in \(2 \text{Cu}^{+}\), copper has an oxidation state of +1.
• Oxygen generally has an oxidation state of -2, except in peroxides or when bonded to fluorine.
  
• Hydrogen usually has an oxidation state of +1 when bonded to non-metals and -1 when bonded to metals.
  
• The sum of all oxidation states in a neutral compound must be zero, and in a polyatomic ion, it must be equal to the ion's charge.

By using the oxidation state rules, you can determine which atoms are getting oxidized and which are getting reduced. This is essential for analyzing redox reactions.

Redox Reactions Analysis

Redox reactions involve the transfer of electrons between atoms. The term 'redox' stands for two processes: reduction and oxidation. Reduction is the gain of electrons, and oxidation is the loss of electrons.

In intramolecular redox reactions, both oxidation and reduction occur within the same molecule. To analyze a redox reaction, follow these steps:

• Identify the reactants and products in the given chemical equation.
• Determine the oxidation states of each atom in both the reactants and products.
• Compare the oxidation states before and after the reaction to see which atoms have been oxidized and which have been reduced.
• Ensure that the total increase in oxidation state (oxidation) is equal to the total decrease in oxidation state (reduction) to comply with the law of conservation of mass and charge.

Let's analyze Reaction 2 as an example: \(2 \text{Cu}^{+} \text{(aq)} \rightarrow \text{Cu} + \text{Cu}^{2-}\). Here:

• Both \text{Cu}\ atoms start with an oxidation state of +1.
• In the products, one \text{Cu}\ atom has an oxidation state of 0 (it has been reduced), and another \text{Cu}\ atom has an oxidation state of +2 (it has been oxidized).

This demonstrates an intramolecular redox reaction, as the same element (Cu) is both oxidized and reduced within the reaction.

Chemical Reactions

Chemical reactions involve the transformation of substances through the breaking and forming of bonds. Reactions can be categorized into different types, such as synthesis, decomposition, single replacement, double replacement, and **redox reactions**.

In redox reactions, one species loses electrons (oxidized), while another gains electrons (reduced). This electron transfer drives the reaction.

For intramolecular redox reactions, both the oxidation and reduction occur within the same molecule or ionic species. Let's consider Reaction 4: \(4 \text{HClO}_{3} \rightarrow 3 \text{HClO}_{4} + \text{HCl}\). Here:

• The chlorine atom in \text{HClO}_{3}\ has an oxidation state of +5.
• In \text{HClO}_{4}\, chlorine has an oxidation state of +7 (oxidization).
• In \text{HCl}\, chlorine has an oxidation state of -1 (reduction).

Thus, chlorine undergoes both oxidation and reduction in the same molecule, confirming an intramolecular redox reaction.

Grasping these concepts not only helps in solving academic problems but also in understanding real-world chemical processes efficiently.