Problem 110 - A Complete Resource Book in Chemistry for JEE Main

Question

Consider the following statements: I. atomic hydrogen is obtained by passing hydrogen through an electric arc II. hydrogen gas will not reduce heated aluminium oxide III. finely divided palladium absorbs large volume of hydrogen gas IV. pure nascent hydrogen is best obtained by reacting \(\mathrm{Na}\) with \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) Which of the above statements is/are correct? (a) I alone (b) II alone (c) I, II, and III (d) II, III and IV

Step-by-Step Solution

Answer

The correct statements are I, II, and III.

Step 1: Evaluate Statement I

Statement I claims that atomic hydrogen is obtained by passing hydrogen through an electric arc. This is true because, in an electric arc, molecular hydrogen () is dissociated into atomic hydrogen ().

Step 2: Evaluate Statement II

Statement II suggests that hydrogen gas will not reduce heated aluminium oxide. This is correct, as hydrogen gas is not reactive enough to reduce aluminum oxide () to aluminum.

Step 3: Evaluate Statement III

Statement III states that finely divided palladium absorbs a large volume of hydrogen gas. This is correct, as palladium is known for its ability to absorb hydrogen, sometimes up to 900 times its own volume.

Step 4: Evaluate Statement IV

Statement IV claims that pure nascent hydrogen is best obtained by reacting sodium () with ethanol (). This statement is incorrect because the reaction produces hydrogen gas (), but not pure nascent hydrogen.

Step 5: Conclusion

After evaluating all statements, we find that Statements I, II, and III are correct, while Statement IV is incorrect.

Key Concepts

Atomic Hydrogen

Atomic hydrogen is a fascinating aspect of hydrogen chemistry. It is essentially hydrogen in its atomic form. In a molecular state, hydrogen is found as \(H_2\), but when it is dissociated into its atomic form, it consists of individual hydrogen atoms \(H\). This dissociation can be achieved by passing hydrogen gas through an electric arc. In this process, the energy from the electric arc breaks the bonds of molecular hydrogen, leading to the formation of highly reactive atomic hydrogen.

Atomic hydrogen is very important because of its reactivity. It can engage in reactions that molecular hydrogen cannot, making it useful in various chemical processes, including the creation of certain types of welds that require high-temperature conditions. Its highly reactive nature comes from the fact that atoms are eager to reach a stable electron configuration, often resulting in more vigorous chemical reactions than their molecular counterparts.

Palladium and Hydrogen Absorption

Palladium is a metal with a remarkable ability to absorb hydrogen. This absorption can be so substantial that palladium can hold up to 900 times its own volume of hydrogen. This is due to its unique lattice structure that allows hydrogen atoms to diffuse and get trapped within it.

When hydrogen is absorbed by palladium, it forms what is known as a palladium hydride. This compound is crucial not just for its theoretical implications but also for practical applications such as hydrogen storage, purification, and sensors. Because palladium can absorb hydrogen so efficiently, it is used in various technologies aiming for clean energy solutions by providing a way to store hydrogen safely and effectively.

The process also allows for the study of hydrogen's behavior in solid-state physics, offering insights into diffusion and absorption mechanisms that could be applicable to other metals.

Reduction Reactions

Reduction reactions in chemistry involve the gain of electrons by a molecule, atom, or ion, and it often involves the reduction of oxides into metals. One interesting aspect of hydrogen in these reactions is its capability to act as a reducing agent. However, this capability is limited by the metal oxides involved.

For example, hydrogen gas can effectively reduce many metal oxides, but it fails to do so with aluminum oxide. This is because aluminum oxide is a very stable compound with strong bonds, and the reduction potential of hydrogen is not enough to break these bonds. As such, methods other than reduction by hydrogen need to be applied to obtain pure aluminum from its ore.

Reduction reactions are essential in metallurgy and other industrial processes where extraction of pure metal from ore is required. Understanding which metal oxides hydrogen can reduce helps in designing and optimizing these processes.

Aluminium Oxide and Hydrogen Reaction

Aluminium oxide, often referred to as alumina, is a crystalline form of aluminum found in nature. It possesses a highly stable structure, which is why it is not easily reduced by hydrogen gas.

The reaction, or more accurately, the lack thereof between aluminum oxide and hydrogen, is an important consideration in the extraction and processing of aluminum. Hydrogen gas does not provide sufficient energy to break the strong ionic bonds present in aluminum oxide. Thus, other methods, like electrolysis, are typically employed to extract aluminum from alumina.

Understanding this interaction, or the absence of it, highlights the importance of selecting appropriate methods for chemical processes based on the unique characteristics of the compounds involved. This kind of understanding is key for chemists and engineers in the development and advancement of efficient extraction techniques.