Problem 62 - A Complete Resource Book in Chemistry for JEE Main

Question

With \(\mathrm{NH}_{4} \mathrm{OH}\), the silver nitrate is decomposed to give a brown precipitate of (a) \(\mathrm{Ag}_{2} \mathrm{O}\) (b) \(\mathrm{AgO}\) (c) \(\mathrm{Ag}(\mathrm{OH})_{2}\) (d) \(\mathrm{NH}_{4} \mathrm{NO}_{3}\)

Step-by-Step Solution

Answer

The precipitate is Ag2O, making (a) the correct answer.

Step 1: Understanding the Reaction

Silver nitrate (AgNO3) reacts with ammonium hydroxide (NH4OH) to form a precipitate. We need to identify the precipitate formed from this reaction.

Step 2: Writing the Chemical Equations

The equations for the reaction between NH4OH and AgNO3 are: 1. AgNO3 + NH4OH → AgOH + NH4NO3 2. AgOH decomposes to Ag2O since AgOH is unstable, producing water (H2O). The reaction results in the formation of Ag2O, which is a brown precipitate.

Step 3: Identifying the Precipitate

Through the reactions, we find that the actual compound formed is Ag2O, which is identified as a brown precipitate.

Key Concepts

Silver Nitrate

Silver nitrate, with the chemical formula \( \text{AgNO}_3 \), is a versatile chemical compound commonly used in various reactions. It's known for participating in precipitation reactions, which involve the formation of solid matter from a solution.

• Highly soluble in water, silver nitrate dissociates in aqueous solutions to form silver ions (\( \text{Ag}^+ \)) and nitrate ions (\( \text{NO}_3^- \)).
• Silver ions are reactive and often participate in reactions where they can form insoluble compounds.

This ability to easily dissociate and provide reactive \( \text{Ag}^+ \) ions makes silver nitrate ideal for use in various chemical experiments, especially those involving the formation of precipitates.

Ammonium Hydroxide

Ammonium hydroxide is a solution of ammonia in water, often denoted as \( \text{NH}_4\text{OH} \). It is a common reagent in labs due to its basic properties.

• The solution is characterized by its ability to react with acids and form precipitates with specific metal ions, such as silver.
• Ammonium hydroxide partly dissociates into ammonium ions (\( \text{NH}_4^+ \)) and hydroxide ions (\( \text{OH}^- \)).

In the case of its reaction with silver nitrate, the hydroxide ions play a key role by reacting with silver ions to form an unstable compound, leading to further decomposition.

Precipitate Formation

Precipitate formation is a type of chemical reaction where a solid substance forms and separates from a solution. This solid is often the product of mixing two aqueous solutions that contain ions that form an insoluble compound.

• In the silver nitrate and ammonium hydroxide reaction, the initial formation is silver hydroxide, \( \text{AgOH} \).
• Silver hydroxide itself is unstable and further reacts to form silver oxide \( \text{Ag}_2\text{O} \), a brown precipitate.

The formation of a visible precipitate, like \( \text{Ag}_2\text{O} \), is an indicator of a chemical change occurring during the reaction. This is observable as the brown solid falls out of the solution.

Decomposition Reactions

Decomposition reactions involve a single compound breaking down into two or more simpler substances. These reactions can be triggered by various factors, such as heat, light, or in the case of \( \text{AgOH} \), inherent instability.

• During the reaction with ammonium hydroxide, silver hydroxide \( \text{AgOH} \) decomposes into silver oxide \( \text{Ag}_2\text{O} \) and water.
• This decomposition highlights the characteristic of \( \text{AgOH} \) being thermodynamically unstable, readily decomposing without external energy.

Understanding decomposition reactions is crucial, as it provides insight into chemical stability and transformations within reactions, explaining the formation of new products like the \( \text{Ag}_2\text{O} \) precipitate.