Problem 15 - A Complete Resource Book in Chemistry for JEE Main

Question

Action of water or dilute mineral acids on metals can give (a) tritium (b) dihydrogen (c) trihydrogen (d) mono hydrogen

Step-by-Step Solution

Answer

The correct answer is (b) dihydrogen.

Step 1: Identify the Reaction

When water or dilute mineral acids react with metals, the general reaction is that the metal replaces hydrogen from the water or acid, releasing hydrogen gas. The chemical reaction can be represented as: \[ \text{Metal} + \text{Acid/Water} \rightarrow \text{Salt/Metal Ion} + \text{H}_2 \text{(gas)} \] This implies the release of diatomic hydrogen gas (\(H_2\)).

Step 2: Analyze the Options

Evaluate each option based on the reaction:- (a) Tritium refers to a radioactive isotope of hydrogen, not related to this reaction.- (b) Dihydrogen (\(H_2\)) is the chemical name for molecular hydrogen gas.- (c) Trihydrogen is not a common term relevant to this topic.- (d) Mono hydrogen doesn't exist as isolated atoms; hydrogen typically exists as diatomic molecules (\(H_2\)).

Step 3: Select Correct Option

Based on the analysis, option (b) is correct because the reaction produces diatomic hydrogen gas or dihydrogen, represented by the formula \(H_2\).

Key Concepts

Dihydrogen

When dealing with chemical reactions involving metals, it's important to understand the role of dihydrogen. This is a common form of hydrogen that naturally occurs as a diatomic molecule, denoted as \(H_2\). Unlike tritium or any non-existent forms like trihydrogen or monohydrogen, dihydrogen is the standard state in which hydrogen atoms pair up.

• Properties: Dihydrogen is a colorless, odorless, and tasteless gas under standard conditions.
• Formation: Dihydrogen is commonly formed during chemical reactions, such as when metals interact with water or acids.

In the context of reactions with metals, the liberation of dihydrogen gas takes place as the metal atoms donate electrons, effectively displacing hydrogen from water or acids. This is why we often see dihydrogen as a product of these reactions.

Reaction with Water

When metals come into contact with water, chemical reactions can occur, leading to the release of hydrogen gas. The specific nature of these reactions depends on the metal involved and the conditions. Generally, more reactive metals readily participate in such reactions.

• Reactive Metals: Metals like sodium and potassium react vigorously with water. The reaction can be exothermic, sometimes causing the hydrogen gas produced to ignite.
• Equation Example: The reaction of sodium with water can be seen in the following equation: \[ 2 ext{Na} + 2 ext{H}_2 ext{O} ightarrow 2 ext{NaOH} + ext{H}_2 \]

In these reactions, the metal typically replaces the hydrogen present in water, leading to the creation of a hydroxide compound and hydrogen gas. Not all metals will react this way; less reactive metals require more rigorous conditions to produce hydrogen gas from water.

Reaction with Dilute Acids

Reactions between metals and dilute acids are another common way to produce dihydrogen gas. When a metal reacts with a dilute acid, it displaces hydrogen ions from the acid.

• Common Acids: Dilute solutions of hydrochloric acid (HCl) and sulfuric acid (H\(_2\)SO\(_4\)) are often used.
• General Reaction: A typical reaction can be represented as:\[ ext{Metal} + 2 ext{HCl} ightarrow ext{Metal Chloride} + ext{H}_2 \]
• Observations: These reactions are often observable due to the effervescence of hydrogen gas bubbles.

The ability of a metal to participate in these reactions depends on its reactivity. Metals such as zinc, magnesium, and even iron usually engage in such reactions with dilute acids to produce dihydrogen.