Problem 51 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following gives propyne on hydrolysis? (a) \(\mathrm{Al}_{4} \mathrm{C}_{3}\) (b) \(\mathrm{Mg}_{2} \mathrm{C}_{3}\) (c) \(\mathrm{B}_{4} \mathrm{C}\) (d) \(\mathrm{L} \mathrm{a}_{4} \mathrm{C}_{3}\)

Step-by-Step Solution

Answer

Mg2C3 gives propyne on hydrolysis.

Step 1: Understanding Hydrolysis and Carbides

The exercise involves selecting compounds that yield specific hydrocarbons when they undergo hydrolysis. Hydrolysis generally refers to a chemical reaction involving water that results in the breaking of bonds in certain substances. For carbides, specifically those containing aluminum and magnesium, they can react with water to yield hydrocarbons. Therefore, our goal is to identify which compound can form propyne through this process.

Step 2: Recall Hydrolysis Reactions of Carbides

Inorganic carbides can react with water during hydrolysis to form different hydrocarbons based on the elements involved. Specifically, aluminum carbide \((\mathrm{Al}_4\mathrm{C}_3)\) when hydrolyzed, forms methane; magnesium carbide \( (\mathrm{Mg}_2\mathrm{C}_3) \) forms propyne; and boron carbide and lanthanum carbide do not produce propyne.

Step 3: Evaluating Each Option

Let's assess each provided option: - \( \mathrm{Al}_4\mathrm{C}_3 \) reacts with water to produce methane, not propyne. - \( \mathrm{Mg}_2\mathrm{C}_3 \) reacts with water to produce propyne. - \( \mathrm{B}_4\mathrm{C} \) does not react in a way to produce propyne. - \( \mathrm{La}_4\mathrm{C}_3 \) also does not produce propyne. Thus, \( \mathrm{Mg}_2\mathrm{C}_3 \) is the correct option.

Key Concepts

Propyne Formation

Propyne is a simple hydrocarbon, specifically an alkyne, with the formula \( ext{C}_3 ext{H}_4\). It contains a triple bond between two carbon atoms, which is characteristic of alkynes. The formation of propyne during the hydrolysis of carbides involves chemical reactions that break down these compounds in the presence of water.

In the exercise you encountered, the compound \(\mathrm{Mg}_2\mathrm{C}_3\) or magnesium carbide, undergoes hydrolysis to form propyne.

This happens because the carbide reacts with water to facilitate the breaking of carbon bonds within the structure. The magnesium element helps stabilize the formation of propyne, resulting in this particular alkyne being produced as a product.

Inorganic Chemistry Reactions

Inorganic chemistry involves studying reactions between different elements and compounds that do not primarily involve carbon, like in organic chemistry. However, its scope also extends to compounds such as carbides where non-metallic elements can form covalent compounds with carbon.

During the chemical process of hydrolysis, inorganic carbides such as \(\mathrm{Mg}_2\mathrm{C}_3\) interact with water. This interaction causes the breakdown of the carbide and the subsequent formation of hydrocarbons.

When water is introduced, it can split into ions, causing the carbide to dissociate and form magnesium hydroxide and propyne in the case of magnesium carbide.

• This showcases the diversity of functional reactions in inorganic chemistry, where elements like magnesium exhibit unique behaviors.
• These reactions are foundational for understanding the conversion processes in chemistry.

Carbides and Hydrocarbons

Carbides are compounds composed of carbon and a less electronegative element, often a metal or metalloid. They form diverse structures and exhibit intriguing chemical reactions, particularly with water.

Different carbides yield various hydrocarbons when hydrolyzed. For instance:

• Aluminum carbide \(\mathrm{Al}_4\mathrm{C}_3\) yields methane, \(\text{CH}_4\).
• Magnesium carbide \(\mathrm{Mg}_2\mathrm{C}_3\) yields propyne, \(\text{C}_3\text{H}_4\).
• Boron and lanthanum carbides do not yield propyne, illustrating their varied reactivity.

Understanding these reactions helps in appreciating how certain chemical processes can bring about different hydrocarbons essential in industrial applications and natural processes.

The capability of producing hydrocarbons from carbides is pivotal in fields such as synthetic chemistry and fuel production. Carbides act as a bridge between simple elemental combinations and complex organic molecules.