Problem 1 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Dihydrogen of high purity \((>99.95 \%)\) is obtained through: (a) the reaction of \(\mathrm{Zn}\) with dilute \(\mathrm{HCl}\). (b) the electrolysis of acidified water using Pt electrodes. (c) the electrolysis of bringe solution. (d) the electrolysis of warm \(\mathrm{Ba}(\mathrm{OH})_{2}\) solution using Ni electrodes.

Step-by-Step Solution

Answer

Option (b): Electrolysis of acidified water using Pt electrodes.

Step 1: Analyze the Reactants and Products

Examine each option and consider the purity of the dihydrogen obtained from the given reactions or processes. The goal is to find which process produces dihydrogen with a purity of greater than 99.95%.

Step 2: Evaluate Option (a)

The reaction of zinc (Zn) with dilute hydrochloric acid (HCl) produces hydrogen gas. Although this reaction generates dihydrogen, the gas is not highly pure as it can contain impurities like zinc chloride and other contaminants from the reaction mixture.

Step 3: Evaluate Option (b)

Electrolysis of acidified water using platinum electrodes produces very pure hydrogen and oxygen gases. Platinum electrodes are inert and do not introduce impurities into the gases, leading to high purity hydrogen above 99.95%.

Step 4: Evaluate Option (c)

The electrolysis of brine solution (saltwater) produces chlorine, hydrogen, and sodium hydroxide. The hydrogen obtained is often impure due to the presence of chlorine and other contaminants.

Step 5: Evaluate Option (d)

Electrolysis of warm barium hydroxide solution using nickel electrodes can yield hydrogen, but this method is less common for generating high-purity hydrogen due to potential contamination from the electrolyte and electrodes.

Step 6: Select the Optimal Process

Among the options, the electrolysis of acidified water using platinum electrodes (Option b) is the most effective method for obtaining dihydrogen with a purity greater than 99.95%.

Key Concepts

Dihydrogen Purity

When talking about dihydrogen, or simply, hydrogen gas, purity is a key factor, especially in applications requiring high precision, like in the food and fuel industries. A purity level of greater than 99.95% is considered extremely high. To achieve such purity, different methods of production offer varying results.
Electrolysis, especially of acidified water using inert electrodes like platinum, can achieve these purity levels. This high purity is primarily due to the limited introduction of impurities during the process, allowing the production of virtually contaminant-free hydrogen. Other methods, such as reacting zinc with hydrochloric acid or electrolyzing brine solutions, often result in lower purity hydrogen due to the potential mixing of other substances.

Platinum Electrodes

Electrodes made of platinum play a critical role in electrochemical reactions, especially when high purity is required. Platinum is known as an inert electrode, meaning it does not react with the electrolyte or the products of the reaction. This property makes it ideal for the production of pure hydrogen through electrolysis.
Why use platinum?

• Inertness: It does not introduce impurities into the reaction, ensuring the gases produced are clean.
• Conductivity: Platinum is an excellent conductor of electricity, which ensures efficient electrolysis.
• Durability: Platinum is resistant to corrosion, meaning it lasts longer, even under rigorous conditions.

This lack of interference and superior performance is exactly why platinum is preferred for obtaining high-purity substances like dihydrogen.

Chemical Reactions in Electrochemistry

Chemical reactions in electrochemistry involve the transfer of electrons which results in chemical change. In the context of the electrolysis of water, we observe water molecules breaking down into hydrogen and oxygen gas.
Here's what happens in electrolytic cells:

• At the cathode, hydrogen ions (\(H^+\)) gain electrons to form diatomic hydrogen gas (\(H_2\)).
• At the anode, water molecules lose electrons, releasing oxygen gas (\(O_2\)).

The overall reaction can be described as: \[ 2H_2O(l) \rightarrow 2H_2(g) + O_2(g) \] This efficient breakdown, particularly when platinum electrodes are used, ensures that we achieve a high level of gas purity free from contaminants. Electrochemistry plays a huge role in energy and material science, providing pathways to obtain essential elements in their purest forms.