Question

Lithium aluminium hydride can be prepared from the reaction of:

• A. \(LiCl \ and \ Al_2H_6\)
• B. \(LiH \ and \ Al_2Cl_6\)
• C. \(LiCl, Al \ and \ H_2\)
• D. \(LiH \ and \ Al(OH)_3\)

Answer 1

The Correct Option is B

Lithium aluminium hydride, commonly known as LiAlH₄, is an important reducing agent in organic synthesis. It is prepared through a specific chemical reaction involving lithium hydride (LiH) and aluminum chloride. Let's analyze the given options to understand which one involves these reactants:

1. LiCl \ and \ Al_2H_6: This combination involves lithium chloride and aluminum hydride. However, these reactants do not produce lithium aluminium hydride.

2. LiH \ and \ Al_2Cl_6: Lithium hydride reacts with aluminum chloride (Al₂Cl₆) to form lithium aluminium hydride according to the following reaction:

   \[ \text{{6LiH + Al}}_2\text{{Cl}}_6 \rightarrow \text{{2LiAlH}}_4\text{{ + 4LiCl}} \]

   This reaction is indeed the correct method to prepare LiAlH₄.

3. LiCl, Al \ and \ H_2: This option suggests the involvement of lithium chloride, aluminum, and hydrogen gas. This combination is not known to produce lithium aluminium hydride.

4. LiH \ and \ Al(OH)_3: Lithium hydride and aluminum hydroxide do not react to form lithium aluminium hydride. This option is incorrect for preparing LiAlH₄.

Thus, the correct answer is LiH and Al₂Cl₆, which react to produce lithium aluminium hydride.