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

(c) 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 a true statement as hydrogen gas can be dissociated into atomic hydrogen when passed through an electric arc due to high temperatures, which break the H-H bonds.

Step 2: Evaluate Statement II

Statement II suggests that hydrogen gas will not reduce heated aluminium oxide. This is a true statement because hydrogen is not a strong enough reducing agent to reduce aluminium oxide, as aluminum is reduced from a highly stable compound.

Step 3: Evaluate Statement III

Statement III states that finely divided palladium absorbs large volumes of hydrogen gas. This is true, as palladium is known for its ability to absorb up to 900 times its volume of hydrogen, storing it as atomic hydrogen in its lattice.

Step 4: Evaluate Statement IV

Statement IV proposes that pure nascent hydrogen is best obtained by reacting sodium with ethanol (\(\mathrm{Na} + \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\)). This statement is incorrect because nascent hydrogen is more commonly generated by reactions such as zinc with sulfuric acid.

Step 5: Determine the Correct Statements

From the above evaluations, we determine statements I, II, and III are correct, while statement IV is incorrect, as nascent hydrogen is not best obtained by the reaction mentioned.

Key Concepts

Reduction of Aluminium Oxide

Reduction of aluminium oxide is a chemical process where aluminium is extracted from its oxide form. Aluminium oxide (\( \mathrm{Al}_2\mathrm{O}_3 \) ) is a very stable compound and reducing it to aluminium metal requires a strong reducing agent. Typically, electrolysis is used for this purpose, as hydrogen gas lacks the strength to serve as a reducing agent here. Some key points to note about this process are:

• Aluminium oxide is not reduced by hydrogen because hydrogen is not powerful enough to break the strong bonds between aluminium and oxygen.
• Electrolysis, rather than a chemical reducing agent like hydrogen, is typically employed for the reduction of metals from their oxides.
• Current industrial processes use the Hall-Héroult process, which involves the dissolution of alumina in molten cryolite, followed by electrolysis.

Understanding why hydrogen gas cannot reduce aluminium oxide helps in clarifying how certain metallurgical processes are specifically designed for different metals, depending on their reactivity and bond strengths.

Hydrogen Absorption by Palladium

Palladium is a fascinating metal, particularly because of its remarkable ability to absorb hydrogen gas. When hydrogen comes into contact with finely divided palladium, an important phenomenon occurs.

• Palladium can absorb up to 900 times its own volume of hydrogen.
• The hydrogen is absorbed into the palladium's lattice structure and is stored as atomic hydrogen.
• This process is reversible, making palladium a useful material in hydrogen storage technologies.

This property of palladium is not only significant in understanding hydrogen storage but also plays a role in catalysis and chemical reactions. The interaction between palladium and hydrogen transforms the hydrogen molecules (\( \mathrm{H}_2 \) ) into single hydrogen atoms, facilitating their involvement in various chemical processes.

Nascent Hydrogen Generation

Nascent hydrogen refers to hydrogen atoms at the moment of their formation, which are highly reactive. This form of hydrogen is often utilized in chemical reactions due to its high reactivity compared to molecular hydrogen (\( \mathrm{H}_2 \) ).There are several methods to generate nascent hydrogen effectively:

• One common method is the reaction of zinc with an acid, such as sulfuric acid, which produces nascent hydrogen.
• This method is more efficient than using the reaction of sodium with ethanol for generating pure nascent hydrogen.
• Nascent hydrogen is sometimes referenced in redox reactions, where its reactivity can reduce other compounds.

Understanding nascent hydrogen is crucial for students exploring topics related to reactivity and the mechanisms of chemical reactions. Its transient nature as a single, highly active atom makes it a significant participant in various chemical processes.