Problem 24 - Chemistry in 30 days

Question

In which reaction does \(\mathrm{SO}_{2}\) act as oxidizing agent (a) Acidified \(\mathrm{KMnO}_{4}\) (b) Acidified \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{1}\) (c) Acidified \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) (d) \(\mathrm{HS}\)

Step-by-Step Solution

Answer

\(\mathrm{SO}_{2}\) acts as an oxidizing agent in reaction with acidified \(\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{OH}\) (option c) and \(\mathrm{HS}\) (option d).

Step 1: Understand the Role of an Oxidizing Agent

An oxidizing agent is a substance that gains electrons in a chemical reaction, and in doing so, it causes another substance to lose electrons. Essentially, the oxidizing agent gets reduced.

Step 2: Consider Acidified \(\mathrm{KMnO}_{4}\) with \(\mathrm{SO}_{2}\)

In the reaction of \(\mathrm{SO}_{2}\) with acidified \(\mathrm{KMnO}_{4}\), sulfur dioxide acts as a reducing agent. It gets oxidized to \(\mathrm{SO}_{4}^{2-}\) while \(\mathrm{Mn}^{7+}\) in \(\mathrm{KMnO}_{4}\) gets reduced to \(\mathrm{Mn}^{2+}\). Thus, \(\mathrm{SO}_{2}\) does not act as an oxidizing agent here.

Step 3: Consider Acidified \(\mathrm{K}_{2}\mathrm{Cr}_{2}\mathrm{O}_{7}\) with \(\mathrm{SO}_{2}\)

Similarly, in the reaction of \(\mathrm{SO}_{2}\) with acidified \(\mathrm{K}_{2}\mathrm{Cr}_{2}\mathrm{O}_{7}\), sulfur dioxide acts as a reducing agent. It gets oxidized to sulfate (\(\mathrm{SO}_{4}^{2-}\)), and chromium (from \(\mathrm{Cr}^{6+}\) in \(\mathrm{K}_{2}\mathrm{Cr}_{2}\mathrm{O}_{7}\)) gets reduced to \(\mathrm{Cr}^{3+}\). Hence, \(\mathrm{SO}_{2}\) does not act as an oxidizing agent here either.

Step 4: Consider Acidified \(\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{OH}\) with \(\mathrm{SO}_{2}\)

In the presence of acidified \(\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{OH}\), \(\mathrm{SO}_{2}\) can oxidize ethanol to aldehydes, such as acetaldehyde. Here, \(\mathrm{SO}_{2}\) acts as an oxidizing agent as it aids in the oxidation of ethanol by gaining electrons.

Step 5: Consider Reaction with \(\mathrm{HS}\)

When \(\mathrm{SO}_{2}\) reacts with hydrogen sulfide (\(\mathrm{HS}\)), \(\mathrm{SO}_{2}\) oxidizes \(\mathrm{HS}\) to sulfur or sulfate ions. In this case, \(\mathrm{SO}_{2}\) acts as an oxidizing agent as it helps in oxidizing \(\mathrm{HS}\) to higher oxidation states.

Key Concepts

Chemical Reactions

Chemical reactions are processes in which substances, known as reactants, transform into different substances, called products. This transformation involves making or breaking chemical bonds, and it leads to a change in properties. Here's a simpler breakdown:

• The molecules of reactants break apart.
• New bonds form to create different molecules, called products.
• These products often have different properties compared to the reactants.

While many types of chemical reactions exist, they can often be classified by the type of chemical change that occurs. For instance, reactions may be exothermic, releasing energy, or endothermic, requiring energy input.
In oxidation and reduction reactions, electron transfer plays a critical role. This type of reaction is crucial in processes like combustion, respiration, and electrolysis.

Sulfur Dioxide

Sulfur dioxide (SO₂) is a colorless gas with a pungent smell synonymous with burnt matches. It's produced naturally from volcanic eruptions and industrially, mainly from burning fossil fuels.

Sulfur dioxide serves multiple roles in chemical reactions, often acting as both a reducing and oxidizing agent depending on the other substances involved. This dual behavior is due to its ability to gain or lose electrons. For instance:

• When reacting with stronger oxidizing agents like acidified KMnO₄, SO₂ acts as a reducing agent.
• When paired with certain reducing agents or compounds like hydrogen sulfide, SO₂ acts as an oxidizing agent.

This versatility makes sulfur dioxide a significant player in a range of chemical processes, and understanding its behavior is crucial in fields such as environmental chemistry and industrial processes.

Oxidation and Reduction

Oxidation and reduction, often abbreviated as redox reactions, are crucial in chemistry. These reactions are all about the transfer of electrons.

Here's how it works:

• Oxidation: This is the process where a substance loses electrons. The substance that gets oxidized increases its oxidation state.
• Reduction: This is the process of gaining electrons. When a substance is reduced, it decreases its oxidation state.
• The oxidizing agent is the substance that gets reduced, while the reducing agent is the one that gets oxidized.

These reactions are essential in various scientific fields, from metabolic pathways in biology to energy storage in batteries. Understanding redox reactions aids in grasping how energy is transferred and transformed in chemical processes.

Electrochemistry

Electrochemistry is the branch of chemistry that examines the relationship between electricity and chemical reactions. It plays a fundamental role in processes that involve electron transfers.

Key concepts in electrochemistry include:

• Electrolytic Cells: These use electrical energy to cause chemical changes.
• Galvanic Cells: These convert chemical energy into electrical energy.
• Redox Reactions: The core of electrochemical processes, involving the flow of electrons.

An understanding of electrochemistry is vital in various applications such as:

• Batteries: converting chemical energy to electrical energy for use in electronic devices.
• Electrolysis: often used in metal plating and water splitting. Sulfur dioxide's behavior as an oxidizing agent in certain scenarios illustrates electrochemical principles at work, showcasing how redox reactions facilitate the movement of electrons.