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

Option (c): I, II, and III are correct.

Step 1: Analyze Statement I

Statement I suggests that atomic hydrogen is obtained by passing hydrogen through an electric arc. This is correct, as an electric arc can break H-H bonds in molecular hydrogen, turning it into atomic form.

Step 2: Analyze Statement II

Statement II states that hydrogen gas will not reduce heated aluminium oxide. This is true, as hydrogen gas typically does not reduce aluminum oxide due to the stability of the oxide.

Step 3: Analyze Statement III

Statement III claims that finely divided palladium absorbs large volumes of hydrogen gas. This is accurate, as palladium can absorb hydrogen gas, forming a palladium-hydrogen system.

Step 4: Analyze Statement IV

Statement IV indicates that pure nascent hydrogen is best obtained by reacting sodium with ethanol (\(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\)). This is incorrect; nascent hydrogen is better produced by reactions like zinc with dilute acids.

Step 5: Match Correct Statements to Option

Statements I, II, and III are correct, which corresponds to option (c): I, II, and III.

Key Concepts

Atomic Hydrogen

Atomic hydrogen, a singular form of hydrogen existing as individual atoms, is typically produced by exposing molecular hydrogen (H₂) to high-energy conditions. One common method involves passing hydrogen gas through an electric arc. This process energizes the molecules, providing enough energy to break the H-H bonds, resulting in free hydrogen atoms.

Atomic hydrogen is highly reactive due to the presence of unpaired electrons in its 1s orbital. This reactivity makes it useful in various industrial applications, such as hydrogenation reactions. Due to its transient nature, atomic hydrogen is often studied under controlled conditions to prevent it from quickly recombining into molecular hydrogen.

Hydrogen Reduction

The process of hydrogen reduction involves the gain of hydrogen atoms by a compound, resulting in its reduction. In the context of metallurgy and chemistry, hydrogen gas is often used as a reducing agent to extract metals from their ores. However, it's important to note that not all metal oxides are susceptible to reduction by hydrogen.

Taking the example of aluminium oxide, hydrogen gas cannot reduce this compound under typical conditions because aluminium oxide is highly stable. The stability is due to the strong ionic bonds between aluminium and oxygen atoms, requiring more energy for disruption than what hydrogen can typically provide in gaseous form. Thus, hydrogen reduction has its limitations, primarily determined by the stability of the oxide involved.

Palladium and Hydrogen

Palladium is a unique metal that exhibits a remarkable capacity to absorb hydrogen gas, a process known as hydrogen absorption or occlusion. Finely divided palladium can absorb up to 900 times its own volume of hydrogen, forming a solid solution with the gas. This property is utilized in many technological applications, such as hydrogen storage and purification.

The interaction between palladium and hydrogen is notable for its ability to form "palladium hydride," an interstitial compound where hydrogen atoms occupy spaces within the palladium lattice. This feature makes palladium highly valued in experiments targeting sustainable energy solutions and catalytic processes.

Nascent Hydrogen

Nascent hydrogen refers to hydrogen atoms that are freshly generated in situ, often exhibiting unique reactivity compared to molecular hydrogen. Nascent hydrogen is typically produced during specific chemical reactions, such as the reaction of certain metals (like zinc) with acids. In these reactions, the hydrogen atoms are in a highly reactive state due to their recent liberation and lack of molecular association.

Contrary to some misconceptions, reacting sodium with ethanol (\(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\)) is not the most efficient method for producing nascent hydrogen. Instead, using zinc with dilute hydrochloric acid or sulfuric acid is preferred, as it yields more substantial and readily usable amounts of nascent hydrogen. This form of hydrogen plays a critical role in organic and inorganic reduction processes due to its enhanced reactivity.