Problem 11 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Lithium aluminium hydride reacts with silicon tetrachloride to form: (a) \(\mathrm{LiCl}, \mathrm{AlH}_{3}\) and \(\mathrm{SiH}_{4}\) (b) \(\mathrm{LiCl}, \mathrm{AlCl}_{3}\) and \(\mathrm{SiH}_{4}\) (c) \(\mathrm{LiH}, \mathrm{AlCl}_{3}\) and \(\mathrm{SiCl}_{2}\) (d) \(\mathrm{LiH}, \mathrm{AlH}_{3}\) and \(\mathrm{SiH}_{4}\)

Step-by-Step Solution

Answer

(b) \(\mathrm{LiCl}, \mathrm{AlCl}_{3}\), and \(\mathrm{SiH}_{4}\).

Step 1: Identify the Reactants and Products

The given reaction involves lithium aluminium hydride (\(\mathrm{LiAlH}_{4}\)) reacting with silicon tetrachloride (\(\mathrm{SiCl}_{4}\)). We need to identify the products formed from this reaction.

Step 2: Analyze the Reaction

Lithium aluminium hydride is a strong reducing agent that typically generates hydrogen-containing products from the halides of non-metals. For the given reactants, one can predict the formation of silicon hydride (\(\mathrm{SiH}_{4}\)).

Step 3: Examine Possible Byproducts

In reactions involving metal hydrides like \(\mathrm{LiAlH}_{4}\), the byproducts often include the accompanying metal halides. Silicon tetrachloride may lead to the production of lithium chloride (\(\mathrm{LiCl}\)) and aluminium chloride (\(\mathrm{AlCl}_{3}\)) as byproducts.

Step 4: Compare Reactions to Options

Given the possible products from the lithium aluminium hydride and silicon tetrachloride reaction—\(\mathrm{LiCl}\), \(\mathrm{AlCl}_{3}\), and \(\mathrm{SiH}_{4}\)—the correct option matches option (b).

Step 5: Confirming the Balanced Equation

To ensure correctness, the overall balanced equation should be reflected as: \[ 4\mathrm{LiAlH}_{4} + \mathrm{SiCl}_{4} \rightarrow 4\mathrm{LiCl} + \mathrm{AlCl}_{3} + \mathrm{SiH}_{4} + \mathrm{AlH}_{3}. \] However, due to options given, (b) accurately simplifies possible products generated here: \(\mathrm{LiCl}\), \(\mathrm{AlCl}_{3}\), and \(\mathrm{SiH}_{4}\).

Key Concepts

Reducing Agents

In chemistry, reducing agents play a crucial role in various types of reactions. Reducing agents are substances that donate electrons to another chemical species, consequently reducing it.
They are critical for processes where the transfer of electrons is involved.
One of the most common results of using a reducing agent is the conversion of a non-metal halide into a hydride.
Lithium aluminium hydride ( LiAlH_4) is a well-known strong reducing agent.
It primarily helps convert halides of non-metals into their corresponding hydrides.
In the case of the reaction between lithium aluminium hydride and silicon tetrachloride, LiAlH_4 donates electrons to SiCl_4, resulting in the production of silicon hydride ( SiH_4).

• Key Features of Reducing Agents: They promote electron transfer.
• They generally lead to the formation of hydrogen-containing products.
• They undergo oxidation while reducing other substances.

Understanding the properties of reducing agents like lithium aluminium hydride allows chemists to predict the products of various reactions, providing insight into the transformation of reactants.

Silicon Tetrachloride

Silicon tetrachloride ( SiCl_4) is a volatile and reactive compound.
It is also a critical compound in silicon-related syntheses and industrial applications.
As a tetrahedral molecule with strong Si-Cl bonds, SiCl_4 serves as both a precursor for silicon-based materials and a participant in chemical reactions.
When introduced to strong reducing agents like lithium aluminium hydride, SiCl_4 undergoes a transformation into silicon hydride ( SiH_4).
This conversion is an excellent example of how a metal hydride can effectively reduce a halide to a hydride.

• Molecular Structure: SiCl_4 has a tetrahedral geometry with silicon at the center and four chlorine atoms at the vertices.
• Reactivity: It reacts readily with reducing agents, participating in electron-transfer reactions.

Knowing the inherent reactivity of SiCl_4 helps students predict its behavior in the presence of different reactants, particularly in its interaction with strong reducing agents.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions.
They illustrate the substance transformation process, from reactants to products.
Writing an accurate chemical equation is fundamental in understanding reactions.
In the context of the lithium aluminium hydride and silicon tetrachloride reaction, the equation is essential for depicting the transition of reactants into specific products.
The balanced chemical equation: \[ 4\mathrm{LiAlH}_{4} + \mathrm{SiCl}_{4} \rightarrow 4\mathrm{LiCl} + \mathrm{AlCl}_{3} + \mathrm{SiH}_{4} + \mathrm{AlH}_{3} \] ensures the number of atoms for each element is balanced, obeying the law of conservation of mass.

• Components: Each chemical equation includes reactants (left side), products (right side), and coefficients to balance atoms.
• Balancing the Equation: Adjust coefficients to ensure the same number of atoms for each element on both sides of the equation.

Mastering the art of writing balanced chemical equations provides clarity regarding the compounds consumed and formed during a reaction.