Problem 74 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is obtained when \(\mathrm{NH}_{4} \mathrm{OH}\) is added to \(\mathrm{AlCl}_{3}\) solution? (a) \(\mathrm{NH}_{3}\) (b) \(\mathrm{NH}_{4} \mathrm{Cl}\) (c) \(\mathrm{NH}_{4}\) (d) \(\mathrm{Al}(\mathrm{OH})_{3}\)

Step-by-Step Solution

Answer

The correct answer is (d) \(\mathrm{Al(OH)}_{3}\).

Step 1: Write the Chemical Equation

When ammonium hydroxide (\(\mathrm{NH}_{4}\mathrm{OH}\)) is added to aluminum chloride (\(\mathrm{AlCl}_{3}\)) solution, a chemical reaction occurs. The balanced equation for this reaction is: \[ \mathrm{AlCl}_{3} + 3\mathrm{NH}_{4}\mathrm{OH} \rightarrow \mathrm{Al(OH)}_{3} + 3\mathrm{NH}_{4}\mathrm{Cl} \] This reaction results in the formation of aluminum hydroxide (\(\mathrm{Al(OH)}_{3}\)) and ammonium chloride (\(\mathrm{NH}_{4}\mathrm{Cl}\)).

Step 2: Identify the Main Product of Interest

The problem asks for the compound obtained when \(\mathrm{NH}_{4}\mathrm{OH}\) is added to \(\mathrm{AlCl}_{3}\). Reviewing the balanced equation, the main noticeable product is the precipitate \(\mathrm{Al(OH)}_{3}\). The other product, \(\mathrm{NH}_{4}\mathrm{Cl}\), will remain dissolved in the solution.

Step 3: Select the Correct Option

The question provides options: (a) \(\mathrm{NH}_{3}\), (b) \(\mathrm{NH}_{4}\mathrm{Cl}\), (c) \(\mathrm{NH}_{4}\), and (d) \(\mathrm{Al(OH)}_{3}\). From Step 2, we determined that \(\mathrm{Al(OH)}_{3}\) is the main product of interest, which corresponds to option (d).

Key Concepts

Ammonium Hydroxide

Ammonium Hydroxide is often described as ammonia dissolved in water, creating what is known as a basic solution. This formula is represented as \( \mathrm{NH}_{4}\mathrm{OH} \). It is a common compound in chemistry labs and everyday products, known for its characteristic pungent smell.

• Composition and Properties: Ammonium Hydroxide is made up of ammonia \( \mathrm{NH}_{3} \) mixed with water. When dissolved, it partially ionizes in water to form ammonium ions \( \mathrm{NH}_{4}^+ \) and hydroxide ions \( \mathrm{OH}^- \).
• Role in Reactions: As a weak base, it donates \( \mathrm{OH}^- \) ions in aqueous solutions, making it useful in neutralization reactions and precipitating metals.

In our reaction between \( \mathrm{NH}_{4}\mathrm{OH} \) and \( \mathrm{AlCl}_{3} \), the \( \mathrm{OH}^- \) ions play a crucial role by facilitating the formation of solid aluminum hydroxide, \( \mathrm{Al(OH)}_{3} \). This makes it a pivotal component in many experimental and industrial procedures.

Aluminum Chloride

Aluminum Chloride, denoted as \( \mathrm{AlCl}_{3} \), is a chemical compound widely used as a catalyst in various reactions. It forms from the combination of aluminum and chlorine and has diverse applications, from the production of aluminum metal to serving as a component in antiperspirants.

• Chemical Nature: In its anhydrous form, it is known as a powerful Lewis acid. When dissolved in water, though, it forms a different set of chloride ions \( \mathrm{Cl}^- \) and aluminum ions \( \mathrm{Al}^{3+} \).
• Importance in Reactions: Its reactivity allows it to participate in many chemical processes, particularly where the generation of a Lewis acid is important, such as in the Friedel-Crafts reactions.

In our specific exercise, \( \mathrm{AlCl}_{3} \) reacts with ammonium hydroxide, resulting in a chemical reaction whereby aluminum chloride provides the aluminum necessary for the formation of \( \mathrm{Al(OH)}_{3} \), a white gelatinous precipitate.

Balanced Chemical Equation

A Balanced Chemical Equation is vital for accurately representing a chemical reaction. It ensures the conservation of mass where the number of each type of atom is the same on both sides of the equation. This concept is fundamental in chemistry as it reflects the law of conservation of mass.

• Importance of Balancing: In chemistry, balancing equations is crucial because it ensures that the reactants and products adhere to fundamental chemical laws. It also provides a clear picture of how much of each substance is involved in the reaction.
• Application in Our Reaction: In the equation \( \mathrm{AlCl}_{3} + 3\mathrm{NH}_{4}\mathrm{OH} \rightarrow \mathrm{Al(OH)}_{3} + 3\mathrm{NH}_{4}\mathrm{Cl} \), each element is balanced across the equation. This ensures that the number of each type of atom on the left equals the number on the right.

Balancing chemical equations allows chemists to predict the amounts of products that will form from given quantities of reactants, and vice versa. This tool is indispensable in both educational and practical chemistry applications.