Problem 43 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is not correct regarding the electrolytic preparation of \(\mathrm{H}_{2} \mathrm{O}_{2}\) ? (a) sulphuric acid undergoes oxidation (b) hydrogen is liberated at anode (c) \(50 \% \mathrm{H}_{2} \mathrm{SO}_{4}\) is used (d) lead is used as cathode

Step-by-Step Solution

Answer

Option (b) is incorrect; hydrogen is liberated at the cathode, not the anode.

Step 1: Identifying the Reaction Process

In the electrolytic preparation of hydrogen peroxide, highly concentrated sulfuric acid undergoes oxidation. The electrolysis process causes sulfuric acid to produce peroxydisulfuric acid, which then hydrolyzes to form hydrogen peroxide.

Step 2: Analyzing Each Option

- (a) Sulfuric acid undergoes oxidation: This statement is correct since the sulfuric acid gets oxidized during electrolysis. - (b) Hydrogen is liberated at the anode: In an electrolytic process, hydrogen is usually liberated at the cathode, not the anode, since oxidation occurs at the anode and reduction at the cathode. - (c) 50% H₂SO₄ is used: This is typically accurate as concentrated sulfuric acid is part of the process. - (d) Lead is used as the cathode: Lead can be used as an electrode material due to its resistance to sulfuric acid.

Step 3: Identifying the Incorrect Statement

Among the options given, option (b) is incorrect because in electrolysis, hydrogen gas is generally liberated at the cathode, not the anode.

Key Concepts

Electrolytic Process

The electrolytic process is foundational in the preparation of hydrogen peroxide (H₂O₂). Through electrolysis, electricity decomposes chemical compounds, causing either oxidation or reduction. In the context of hydrogen peroxide production, electrolysis involves concentrated sulfuric acid (H₂SO₄).
When sulfuric acid undergoes electrolysis, it oxidizes, facilitating the formation of peroxydisulfuric acid (H₂S₂O₈). This intermediate is crucial because, upon hydrolysis, it yields hydrogen peroxide.

• Electrolysis serves as a driving force for chemical changes.
• It breaks down molecules using electrical energy.
• The process is integral to generating H₂O₂ through oxidation reactions.

By comprehending the dynamics of electrolysis, one gains insights into how electrical energy transforms chemical substances into desired compounds. It's this precise manipulation that forms the backbone of electrolytic preparation in chemical industries.

Sulfuric Acid Oxidation

In the production of hydrogen peroxide, sulfuric acid plays a pivotal role, primarily through oxidation. Oxidation refers to the chemical reaction where a substance loses electrons. Sulfuric acid (H₂SO₄) undergoes such a reaction during the electrolytic process.
This change results from the addition of oxygen or the reduction in hydrogen content. The transformation leads to the creation of peroxydisulfuric acid, which, upon hydrolysis, decomposes into hydrogen peroxide.

• Oxidation is crucial for converting sulfuric acid into peroxydisulfuric acid.
• It highlights the importance of sulfuric acid as a reactive agent.
• The oxidative pathway is necessary for forming intermediate compounds.

Understanding sulfuric acid oxidation illuminates the chemical steps involved in generating hydrogen peroxide—a common chemical in bleaching and disinfection applications.

Electrode Materials

Electrode materials are critical in any electrolytic process, including the production of hydrogen peroxide. They facilitate the flow of electricity and enable reactions at their surfaces. The choice of electrode material affects the efficiency and outcome of the process.
In the preparation of hydrogen peroxide via electrolysis, lead is often used as an electrode material. It acts as the cathode, thanks to its resistance to sulfuric acid, minimizing corrosion and ensuring durability in acidic environments.

• Electrode materials need to be conductive and chemically inert.
• They play a vital role in enabling the redox reactions.
• Lead's use showcases its utility in acidic solutions, thanks to its resistive qualities.

Understanding the function and selection of electrode materials enhances knowledge about the intricacies and efficiency of electrolytic systems and their chemical outputs.